The popularity of 3-phase induction motors onboard ships is due to their simple, robust construction and high reliability in the sea environment. An induction motor can be used for various speed and load requirements applications.

The ship’s generator’s 3-phase AC supply can be connected to the AC induction motor via a starter or any other arrangement, like an auto-transformer, to improve the torque and current characteristics.

Related Reading: Why Are Transformer And Alternator Ratings in kVA On Ships?

Induction motors are used in almost all ship machinery systems, such as crane motors, propulsion motors, blower motors, seawater pump motors, and even small synchronous motors.

What is an Induction Motor?

An induction motor or asynchronous motor is an AC motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.

There are two types of an induction motor:

1. Single Phase Induction Motor:

Single-phase induction motor: As the name suggests, this type of motor is supplied with a single-phase power supply. AC current is carried in the main winding of the motor. The type of single-phase induction motor used depends on the starting arrangement used as an auxiliary, as they are not self-starting.

Single-phase induction motors are primarily used in low-power applications, some of which are mentioned below:

• Small pumps
• Small portable compressors
• Small fans
• Drilling machines

2. 3 Phase Induction Motor

These 3 phase motor is supplied with 3 three-phase AC supply and is widely used in ships for heavier loads. 3 phase induction motors are of two types: squirrel cage and slip ring motors.

Squirrel cage motors are widely used on ships due to their rugged construction and simple design, few e.g. of their applications are:

• Lifts
• Cranes
• Large capacity exhaust fans
• Engine Auxiliary pumps
• Engine blower fan motor
• Engine room heavy load pumps –Ballast, Fire, Freshwater, Sea Water etc.
• Winch motor
• Windlass motor

Related Reading: General Overview Of Central Cooling System On Ships

Construction of 3 Phase Induction Motor

The main body of the Induction Motor comprises of two major parts:

Stator

The stator is made up of a number of stampings in which different slots are cut to receive 3 phase winding circuit which is connected to 3 phase AC supply.

The three-phase windings are arranged in the slots so that they produce a rotating magnetic field after an AC supply is given to them.

Related Reading: How To Overhaul Motors On Ships?

Usually, windings are kept at different pitch circles with 30 % overlap with each other.

The windings are wound for a definite number of poles depending upon the speed requirement, as speed is inversely proportional to the number of poles, given by the formula:

N_s= 120f/p

Where N_s= synchronous speed

f  = Frequency

p = no. of poles

Rotor

The rotor consists of a cylindrical laminated core with parallel slots that carry conductor bars.

Conductors are heavy copper or aluminium bars which fit in each slot. These conductors are brazed to the short-circuiting end rings.

The slots are not precisely made parallel to the axis of the shaft but are slotted a little skewed for the following reasons:

• They reduce magnetic hum or noise
• They avoid stalling the motor

Principle and Working Of 3 Phase Induction Motor

When 3 phase supply is given to the motor, the resulting current generates a magnetic flux “Ø”.

Due to the switching sequence of 3 phase current in R, Y, and B, the generated flux rotates around the rotor conductor.

According to Faraday’s law, which states that –“an emf induced in any closed circuit is due to the rate of change of magnetic flux through the circuit”, Emf is induced in the Copper bar and due to this, current flows in the rotor.

The direction of the rotor can be given by Lenz law which states that – “the direction of induced current will be in the opposite of the motion causing it.”

Here, the relative velocity between the rotating flux and static rotor conductor causes current generation; hence, the rotor rotates in the same direction to reduce the cause, i.e., the relative velocity, thus rotating the induction motor’s rotor.

Advantages of Induction Motor

The motor construction and the way electric power is supplied give the induction motor several benefits, such as:

– They are robust and simple in construction, with very few moving parts

– They can efficiently operate in a rugged and harsh environment, such as in seagoing vessels

– The maintenance cost of 3-phase induction motor is less, and unlike that of a DC or synchro motor, they do not have parts like brushes, commuters, slip rings etc.

– An induction motor can operate in an intrinsic environment as they do not have brushes, which can cause the spark and can be dangerous to such an atmosphere

Related Reading: 20 Hazards Of Oil Tanker Ship Every Seafarer Must Know

– The 3-phase induction motors do not need any additional starting mechanism or arrangement as they can generate self-starting torque when a three-phase AC supply is provided to them, unlike synchronous motors. However, the single-phase induction motor needs some auxiliary arrangement for the starting torque

– The final output of a three-phase motor is nearly 1.5 times the rating (output) of a single-phase motor of the same size.

Disadvantages of 3 phase Induction motor:

– During starting, it draws high initial starting current when attached to a heavy load. This causes a dip in voltage during the starting period of the machine. Soft starting methods are connected to the 3 phase electric motor to avoid this problem.

Related Reading: Motor Starter Panel On Ships: Maintenance And Routines 

– Induction motor operates at lagging power factor which results in increased I2R losses and efficiency reduction, especially at low load. To correct and improve the power factor, static capacitor banks can be used with this type of AC motor.

– Speed control of 3-phase induction motor is difficult as compared to DC motors. A variable frequency drive can be integrated with the induction motor for speed control.

Problems in 3 phase Induction motor:

Like any other machinery, a 3-phase induction motor can face various types of challenges, which can be broadly classified as:

A) Environmental-related faults: The harsh environment of the sea may take a toll on the ship’s machinery at an early stage if it is not maintained correctly. The ambient temperature and the moisture content in the sea air will affect the induction motor’s operational performance.

The motors are installed on other big machinery (main engine), and each has its own vibrating frequency, which affects the motor parts.

A wrong installation or loose foundation of the motor or the load it is connected to may also reduce the motor’s efficiency and, in the long run, cause its failure.

B) Electrical-related faults: Problems occur in the motor due to electrical supply faults such as the unbalanced supply of current or line voltage, earth fault in the system, single phasing, short circuit, etc. Different types of electrical faults are:

Winding Fault: The winding provided in the stator may fail due to the problem in the insulation caused leading to short circuit.

Related Reading: Importance Of Insulation Resistance In Marine Electrical Systems

Single Phasing Fault: When any one or more than one phase of the 3-phase supply is lost, a running 3-phase motor will continue to run but at elevated parameters of temperature and loss. This condition is known as single phasing.

Crawling: This is a mix of electrical and mechanical faults where the induction motor runs at a lower speed (nearly 1/7th of its synchronous speed) even at complete load application. It results from abnormal magnetomotive force or high harmonic content in the power supply to the motor.

C) Mechanical-related faults: The motor consists of several mechanical parts, and their alignment with each other and the load plays an essential role in motor efficiency. Some of the prominent mechanical-related motor faults are:

1. Imbalance Rotor: The rotor is the only moving part in a 3-phase induction motor. If there is an imbalance between the shaft rotational axis and the weight distribution axis of the rotor, it will create vibration, additional heat and efficiency loss in the system.

The unbalance can be due to a defect in the rotor, internal misalignment, bending of the shaft, uneven loading, or problems in the motor and load coupling.

Related Reading: 10 Things To Consider While Reassembling Ship’s Machinery After Maintenance 

2. Fatigue Failure: If the maintenance schedule is improper or the parts used in the motor are of poor quality, material weakening may lead to fatigue failure, usually caused by repeatedly applied loads.
3. Bearing failure: The motor is fitted with two bearings at each end of the rotor for supporting and freely rotating the shaft. The bearing can fail if timely maintenance is not done or due to overloading, wrong installation, contaminated lube oil, or operating at an excessive temperature.

Related Reading: How to Test Lubricating Oil On Board Ships?

4. Corrosion: The surroundings of the motor installed in a ship are highly corrosive. As the motor consists of several mechanical parts like the rotor, bearing, etc., the moisture present in the atmosphere or the water present in the lubrication (grease) will corrode the bearings, motor shaft and rotors. The insulation can also be affected by the corrosion, and lead to a short circuit between the windings.
5. Lubrication problem: Lack of lubrication or contamination of the lubricant can increase friction between parts, and bearings may wear out quickly.

Related Reading: 8 Ways to Optimise Lubricating Oil Usage On Ships

Protections for 3-phase induction motor

Single-phasing protection: To tackle this problem, protection devices are used for 3-phase induction motors. All motors above 500 KW are to be provided with protection devices or equipment to prevent damage due to single-phasing. The details of these devices can be found here. 

Over-temperature: The motor’s winding can be heated due to problems like overloading or single phasing. Fuses, relays etc., are used to protect the motor from overheating.

Related Reading: Maintenance of Electrical Relay in Ships Electrical System

Soft Starting: As described above one of the disadvantages of 3 phase induction motor is the high current it draws during the starting period. To protect it from this problem, different starting method are used by integrating the motor with soft starter, DOL, Star delta starter, autotransformer etc.

Related Reading: 10 Ways To Achieve Energy Efficiency In Ship’s Electrical System

Using a soft starter for an induction motor reduces mechanical and electrical stresses, protecting the motor during the starting time.

You might also like to read:

• How to Minimize the Risks of an Electrical Shock on a Ship?
• 10 Ways to Achieve Energy Efficiency in Ships Electrical System
• Single Phasing in Electrical Motors: Causes, Effects, and Protection Methods
• Maintenance of Electrical Relay on Ships Electrical Circuit
• 10 Electrical Jobs Marine Engineers Must Know On Board Ships

Disclaimer: The views mentioned above are of the author only. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

3 Phase Induction Motor – Construction and Working appeared first on Marine Insight - The Maritime Industry Guide

Several electrical machines and panels are fitted onboard ships to sail from one port to another safely and efficiently.

The electrical machinery and system require scheduled maintenance and checks to avoid any breakdown during sailing.

Different instruments are used onboard for measuring several electrical parameters to analyze and keep these machines in proper running condition.

A permanent magnet moving coil (PMMC) is one such instrument that is popularly used onboard and has several applications. The other popular nomenclature of this instrument is D’alvanometer and galvanometer.

Permanent Magnet Moving Coil: Principle of Working

When a current-carrying conductor is placed in a magnetic field, it experiences a force and tends to move in the direction as per Fleming’s left-hand rule.

Fleming left-hand rule:

If the first and the second finger and the thumb of the left hand are held so that they are at a right angle to each other, then the thumb shows the direction of the force on the conductor, the first finger points towards the direction of the magnetic field and the second finger show the direction of the current in the wire.

Equation involved

The interaction between the induced field and the field produced by the permanent magnet causes a deflecting torque, which results in rotation.

The three important torque involved in this instrument are:

Deflecting torque:

The force F, which will be perpendicular to both the direction of the current flow and the direction of the magnetic field as per Fleming’s left-hand rule, can be written as

F = NBIL

where N: turns of wire on the coil

B: flux density in the air gap

I: current in the movable coil

L: vertical length of the coil

Theoretically, the torque (here electro-magnetical torque) is equal to the multiplication of force with distance to the suspension point.

Hence Torque on the left side of the cylinder T_L = NBIL x W/2 and torque on the right side of the cylinder T_R = NBIL x W/2

Therefore the total torque will be = T_L + T_R

T = NBILW or NBIA where A is an effective area (A= LxW)

Controlling Torque

This torque is produced by the spring action and opposes the deflection torque so as the pointer can come to rest at the point where these two torques are equal (Electromagnetic torque = control spring torque). The value of control torque depends on the mechanical design of spiral springs and strip suspensions.

The controlling torque is directly proportional to the angle of deflection of the coil.

Control torque C_t =Cθ where, θ = deflection angle in radians and C = spring constant Nm /rad .

Damping torque

This torque ensures the pointer reaches an equilibrium position, i.e. at rest in the scale, without oscillating to give an accurate reading. In PMMC, as the coil moves in the magnetic field, eddy current sets up in a metal former or core on which the coil is wound or in the circuit of the coil itself, which opposes the motion of the coil, resulting in the slow swing of a pointer and then come to rest quickly with very little oscillation.

Construction of PMMC

A coil of thin wire is mounted on an aluminium frame (spindle) positioned between the poles of a U shaped permanent magnet, made up of magnetic alloys like alnico.

The coil is pivoted on the jewelled bearing, and thus the coil is free to rotate. The current is fed to the coil through spiral springs, which are two in numbers. The coil which carries a current, which is to be measured, moves in a strong magnetic field produced by a permanent magnet and a pointer is attached to the spindle, which shows the measured value.

Working of PMMC

When a current flows through the coil, it generates a magnetic field proportional to the current in an ammeter. The deflecting torque is produced by the electromagnetic action of the current in the coil and the magnetic field.

When the torques are balanced, the moving coil will stop, and its angular deflection represents the amount of electrical current to be measured against a fixed reference, called a scale. If the permanent magnet field is uniform and the spring linear, the pointer deflection is also linear.

The controlling torque is provided by two phosphorous bronze flat-coiled helical springs. These springs serve as a flexible connection to the coil conductors.

Damping is caused by the eddy current set up in the aluminium coil, which prevents the oscillation of the coil.

Applications

The PMMC has a variety of uses onboard ships. For example, it can be used as:

1)      Ammeter:

When PMMC is used as an ammeter, except for a minimum current range, the moving coil is connected across a suitable low-resistance shunt so that only a small part of the main current flows through the coil.

The shunt consists of several thin plates of alloy metal, which is usually magnetic and has a low-temperature coefficient of resistance, fixed between two massive blocks of copper. A resistor of the same alloy is also placed in series with the coil to reduce errors due to temperature variation.

2)      Voltmeter:

When PMMC is used as a voltmeter, the coil is connected in series with high resistance. The rest of the function is the same as above. The same moving coil can be used as an ammeter or voltmeter to interchange the above arrangement.

3)      Galvanometer:

The galvanometer is used to measure a small value of current along with its direction and strength. It is mainly used on board to detect and compare different circuits in a system.

5)      Ohm Meter:

The ohmmeter is used to measure the resistance of the electric circuit by applying a voltage to resistance with the help of a battery. A galvanometer is used to determine the flow of current through the resistance. The galvanometer scale is marked in ohms, and as the resistance varies since the voltage is fixed, the current through the meter will also vary.

Advantages of PMMC

• The PMMC consumes less power and has great accuracy.
• It has a uniformly divided scale and can cover an arc of 270 degrees.
• The PMMC has a high torque to weight ratio.
• It can be modified as an ammeter or voltmeter with suitable resistance.
• It has efficient damping characteristics and is not affected by a stray magnetic field.
• It produces no losses due to hysteresis.

Disadvantage of PMMC

• The moving coil instrument can only be used on D.C supply as the current reversal produces a torque on the coil.
• It’s very delicate and sometimes uses an AC circuit with a rectifier.
• It’s costly as compared to moving coil iron instruments.
• It may show an error due to the loss of magnetism of the permanent magnet.

What are the different reasons that cause an error in PMMC?

1. Temperature effect: Error in the reading of the PMMC may cause a change in the temperature, which will affect the resistance of the moving coil. The temperature coefficients of the value of the coefficient of copper wire in the moving coil are 0.04 per degree Celsius rise in temperature. Since the coil has a lower temperature coefficient, it will have a faster rate of temperature rises, resulting in an increase in the resistance, causing an error.

2. Spring material and age: The other factor which may lead to error in the PMMC reading is the quality and contortion of the spring. Old ageing spring will not allow the pointer to show the correct reading making an error.

3. Ageing of Magnet: Along with age, the effect of heat and vibration will reduce the magnetic effect of the permanent magnet, which will produce an error in the reading.

Can PMMC be used to measure AC?

If the frequency is low enough, the PMMC with a rectifier can measure AC, which converts the measured quantity into a DC typically less than 1mA. Add an appropriate scale, and you have a meter.

What will happen if I use it with high-frequency AC?

If the frequency of AC is high, the meter vibrates in and around the zero value (preferable to verify with a centre zero meter) and finally stops responding to the AC.

What are permanent magnets made of?

Permanent magnets are made of special alloys such as :

• Aluminum-Nickel-Cobalt (Alnicos)
• Strontium-Iron
• Neodymium-Iron-Boron
• Samarium-Cobalt.

SaveSave

Permanent Magnet Moving Coil Instrument (PMMC) – Working and Application appeared first on Marine Insight - The Maritime Industry Guide

If you are new to a ship, the first few days might leave you confused, lost, and extremely apprehensive as to how are you going to spend the rest of your days of your contract on the ship safely without confronting any accidents.

The huge matrix of pipes, the complex machinery, and the massive bunch of wires which runs without any restrictions in different directions might leave you a bit messed up in your mind. It is during this vulnerable mindset, you can come across the worst accident that has happened to you.

When we talk about accidents on a ship, an electrical shock is the worst of all kinds. Electrical wires and connections are present everywhere on a ship and it is important to escape them to prevent yourself and others from getting a major electrical shock.

Moreover, it is said that a person onboard a ship gets an electrical shock mainly due to its negligence and unawareness.

In this article, we will learn how you can save yourself and others from an electrical shock on board a ship.

Also, find out what all precautions you should take to minimize the risk of an electrical shock on board.

 Steps to Minimize the Risk of an Electrical Shock Onboard

1)    Start with the first round of the day; check all electrical motors, wiring, and switches, for abnormal sounds, variation in temperatures, and loose connections.

2)    Ensure that all electrical connections are inside the panel box so that no one can touch them accidentally.

3)    In the accommodation area multiple socket plugs shouldn’t be used.

4)    Turn off the breaker before starting any work on an electrical system.

5)    Use ply card and notice board as much as possible to inform others about the ongoing work to avoid accidental starts.

6)    Double check the electrical tools like portable drills for any loose wires before attempting any job.

7)    Always wear protective clothing, rubber gloves, rubber knee pads and safety shoes to avoid the risk of shock.

8)    Use electrically insulated handle tools for working or checking the electrical system.

9)     Before working, remove the jewellery wristband and other conductive items.

10) When working or removing multiple wires, tape off all but the one wire you are working on.

11) Try as much as possible not to work on a live system and even if you do so by a professional and work carefully with full concentration.

12)  During working in a group or pair, organise a toolbox meeting and discuss the procedure, risk and hazards of the job at hand.

13)  If you don’t know about the system, ask for assistance. Don’t work without knowing it.

14) Always think about your own safety and the safety of fellow persons while carrying out any electrical work.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

How to Minimize the Risks of an Electrical Shock on a Ship? appeared first on Marine Insight - The Maritime Industry Guide

In spite of the the latest advancements in maritime navigation technologies such as GPS, ECDIS, and several other satellite signaling systems, navigation lights still play an important role in navigation of ships at sea.

These signaling lights have been an integral part of the ship navigation procedures since decades and because of their frequent usage, are included in the routine maintenance procedures.

Navigation lights are used while navigating a vessel near coastal areas, in heavy shipping traffic areas, maneuvering at a harbor, or simply sailing out at the sea. They help in indicating the ship’s position, status, direction of course etc. to other nearby vessels for avoiding collision at the sea. This is the first form of non-verbal communication that is made by a ship to the nearby vessels during navigation.

Ship’s navigation and signal lights are located in those areas, which make  them easily noticeable even from a far distance. However,  when it comes to maintenance of these lights, such high locations are quiet dangerous to access especially when the ship is at open seas.

The three important locations for navigation lights on ships are

• Fore mast
• Main mast
• Aft signal light station

Maintenance of Ship Navigation lights

Following safety procedures must be followed before doing any maintenance work on ship navigation lights

• Prepare the work permit
• Put the lock out tag and inform the officer who is on duty
• Try to do the routine maintenance when the ship is in the port
• Before climbing up the main mast, take the working aloft permit
• Switch off the radars and take out the fuses
• Disable the power supply of the nearby ship whistle
• Switch off any other communication devices as the antennas, which are usually located near the mast, generate radiations harmful for humans
• While working on navigation lights at sea, check the wind flow meter for wind speed and direction. If the wind is heavy avoid climbing on the mast
• Check for rolling and pitching of the ship. If it’s too much, don’t climb the mast
  

Factors Affecting Navigation Lights and Procedure for Maintenance 

Maintenance of marine navigation lights is extremely important for safety of ships. These lights are located on the ship’s outside, at highest places of the vessel. The following factors thus affect these lights:

a) Water (sea and rain water)

b) Vibrations

c) Sun light and wind

d) Wire securing

Let’s understand how each factor affects the navigation lights.

A) Water (Sea water and Rain water)

Water is a major threat to all the electrical systems onboard. Water ingress can cause fire in the electrical systems because of short circuit. Since all the navigation lights are located outside on the ship’s deck, they are prone to harmful effects of seawater, rainwater and atmospheric moisture.

The navigation lights are thus placed in weather tight and watertight enclosures. However, even though these casings are weather proof, there are high chances of water penetration due to leakage in the system because of rust formation and frequent opening of enclosures for replacing bulbs.

Note: If the bulb of a navigation light is frequently getting fused, this is an indication of water ingress inside the circuit.

Points to consider:

• Periodically check the light fittings for leakage of water
• Ensure to apply water resistant material like silicon or putty whenever the light fitting is opened up for replacing the bulbs
• Visually, check inside the casing for any salt formation. If salt formation is found, it means that the sea water has penetrated inside.
• Take fine clothes and cleaners for cleaning the glasses of the light fittings for good illumination/signaling
• Check the light holders inside the fittings for corrosion or fungus formation
• Use the contact cleaners for cleaning purpose whenever the light fitting is opened up 

B) Vibrations

There is no place on the ship where vibrations generated from operating ship’s engine room machinery don’t reach. Since the navigation lights are located at the highest points of the vessel, they are always under the effect of vibrations when main engine is running. This is yet another cause of bulb failure.

• Ensure to use vibration absorber material like rubber gasket material wherever possible.
• While working on the navigation lights, check for any loose nut bolts and holders. Tighten and secure them whenever necessary.
• Use washers where nut bolts are used in light fixtures to avoid loosening of the nuts
• Clamp the structure where the light fixture is installed.

C) Sun light and wind

This is one factor affecting marine navigation lights wherein nothing much can be done.

Due to continuous sunlight, the life of the light fittings often get reduced especially if they are made of plastic. Thus it’s always better to install weatherproof brass material light fittings.

D) Wire Securing

More than often, the wires of navigation lights that are secured to the mast, get tangled or loosen due to weather exposure. Do check for any loose connections of the wire and secure the wires using cable wires. Keep a regular check on the condition of these wires.

All the navigation lights on ships are installed in pairs, i.e. two in numbers. If one fails, the other one replaces it. However, it is important that officers in charge perform routine maintenance checks on these lights and also check the light/ bulb failure alarms for the same.

What maintenance procedures do you follow for navigation lights on ships?

How Maintenance of Navigation Lights is Done On Ships? appeared first on Marine Insight - The Maritime Industry Guide

A busbar is a copper plate/bar which is used in ship’s main and emergency switchboards to conduct electricity from generators or from one electrical terminal to another. Technically, there are no electrical wire connections inside the main and emergency switchboards on ships for connecting Power supply from generators to these switchboards. All high voltage and high current systems are connected by bus bars.

The busbar’s copper plates/ bars are connected together with the help of nut bolts, which transmit electricity as required. During normal ship operations, the busbar connections are subjected to ship’s harsh environment along with the vibrations generated by the ship and ship machinery such as Main Engine, auxiliary engines, compressors etc. These vibrations cause loosening of nut bolts in the busbar, which can lead to short circuit or any other type of accident. Loose connections inside the switchboard can also lead to sparks that can cause fire.

Moreover, the busbars are meant to carry high voltage and current which tend to heat up the lines due to energy flow in the system. For this reason, inspection and maintenance of busbar at regular inspection of time are required for smooth operation.

Safety

If any maintenance is planned for busbars, highest standards of safety are required as even the tiniest mistake can lead to electrocution and even death. The busbar maintenance is therefore performed when the complete busbar panel or Switchboard is turned “OFF”. Following are the precautions for safety to be carried out when the bus bar maintenance is to be carried out:

When the bus bar maintenance should be done?

1. Bus bar maintenance can be done when the ship is in black out condition, i.e. ship’s generators are not running and no power is supplied to main or emergency switchboards
2. If the main switchboard busbars are to be inspected or to be work on, keep emergency generator running. Keep in mind that there will be some portion of the main switchboard which will be fed by emergency switch board. Hence know the complete system properly and keep away from those areas
3. The best time to do bus bar maintenance is when the ship is in the dry dock

Safety before doing bus bar maintenance:

1. Put the “lockout” tag in all generators and in the emergency generator
2. Keep all the generator system including load dependent start stop system in manual mode
3. Ensure to wear rubber gloves even when the board is not in “Live” condition
4. Wear all required personal protective equipment (PPEs) when working on switchboard
5. If the ship is in complete black out situation, ensure that before cleaning the main and emergency switchboard, the area is well lit by sufficient lights.  In dry dock same can be arranged from shore workshop

How Busbar Inspection and maintenance is carried out?

Any maintenance on busbars should only be performed when the ship in Dry dock or Black out condition:

1. Open the door for main and emergency switchboards where inspection is to be performed
2. Carryout visual inspection of copper plate and nut bolts. Mark any missing or burn out areas
3. By hand or using a metal or plastic stick (where access for hand is not possible), tap the bus plates gently so as to make out for any loose connection. Ensure to wear electrical gloves even when bus bar is not live
4. The busbars are mechanical supported inside the switchboard by means of insulators, which may be of rubber or ceramic materials (bad conductors). Check for any damages in the insulator part
5. By using only dedicate size spanner or pre adjusted torque wrench, tighten the nuts in the busbar connection for main and emergency switch boards
6. Check the tightness of the wire connections, which is connected to the circuit breakers
7. Clean the bus bar and switchboard area with the help of vacuum cleaner
8. If u find any loose connection or spark, black-out the particular and adjacent bus bar before tightening the nut
9. If u find any metal piece or nut bolts missing or inside the panel, ensure to remove it as the same can cause short circuit or fire

The ship’s electrical officer is required to inspect the busbar periodically for record keeping and also as stated by the preventive maintenance system. This is done to avoid any type of accident from electrical faults on ships. When doing such inspection the following highest safety measures are to be taken with all required PPEs as the Bus bar is “LIVE”:

• Check the load in the running generator by means of KW meter provided in the main switchboard.
• Open the bus bar access door provided at the backside of MSB or ESB.
• Do the visual inspection and by the help of infrared temperature gun, measure the temperature of copper plates and bus bar connection.It should not be more than given limits depending upon the generator load. Example if the generator load is 50%, the room temperature is 28 deg c, the bus bar temperature must be within 50 deg c, if the temperature is too high then some thing is abnormal.

Once the inspection and maintenance is completed:

1. Close the bus bar access doors
2. Remove the lock out tag
3. Restore the main power supply by the generators
4. Inform the Chief Engineer and the in-charge of that particular machinery regarding the same
5. Reset the main power and check if there is any abnormal sound in main switch board and emergency switch board
6. Monitor the temperature of the busbar area with laser temperature gun
7. Keep the emergency switchboard in the auto mode

How do you carry out busbar maintenance on board ships? Let us know in the comments below.

How to Do Busbar Inspection and Maintenance on Ships? appeared first on Marine Insight - The Maritime Industry Guide

With new stringent regulations against pollution being introduced, it is important for the manufacturers to build marine engine that satisfy these norms and do not hamper the normal operation of the engine. To achieve this, engines are provided with several automation systems, which not only reduce the pollution level but also increase the efficiency of the engine and reduce other operational cost.

One such introduced automation is lambda control which controls the fuel injection system of the marine engine according to the variation in the load on the same.

Purpose of Lambda Controller

The main function of any engine is to supply enough power so that it can handle the load put on it. The load may increase or reduce during the operation and to accompany this, some excess fuel may be given to keep up the performance.

Lambda controller is used to control the excess fuel injection in the combustion chamber of a marine engine when there is a change in the engine load i.e. during a momentary increase in the engine load.

This is done by controlling the two main elements which are responsible for combustion- fuel and air. This controller senses the relation between the charge air pressure and fuel index of the engine at that load.

Principle of Working

The working of Lambda controller can be understood with the help of the following diagram:

When there is a sudden momentary increase in the engine load, the lambda control will regulate the fuel through injection pump using the regulator arm. For this, (1) is turned on which in-turn commands the switch (2) to touch the Piston arm (3) and be pushed downward, where in the electric circuit will be closed.

Hence, solenoid valve (4) will open which will then actuate the jet system to accelerate the turbocharger resulting in increase in charged air pressure. This will result in pressing the piston (3) back in the lambda cylinder (5). When the lambda value or lambda ratio is satisfactory, then the solenoid valve will get closed, deactivating the jet system.

When the system is activated for more than 10 seconds, then the solenoid valve is signaled to shut off and there is an alarm for system failure

Fuel oil limiting during start

During the start procedure, the lambda controller is used as an index limiter.

Hereby heavy smoke formation is prevented during start procedure and the regulating device cannot over-react.

Advantages

• It reduces the emission of excess visible smoke when there is a sudden increase in engine load.
• The overall load efficiency of engine increases.
• The exhaust side of the engine .i.e. exhaust valve, exhaust gas way, exhaust uptake etc are less fouled due to carbon deposits.
• The maintenance work reduces due to less fouling of parts.

You may also like to read-What is Oil Discharge Monitoring and Control System (ODMCS)

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Most of the motors in the ship’s engine room are continuous running motors connected to a pump or compressor or some other machinery. Like any other mechanical machinery, motors also have their own running hours, after which, the complete overhauling of the motor is to be done to ensure efficient working and performance. Also, if any other parameters such as voltage, current or insulation resistance is abnormal or the motor came in contact with water (due to flooding or water leakage), the overhauling of motor is to be performed.

Overhauling a Motor

In motor construction, the air gap between the stator and the rotor is very less. If there is a little deviation in the shaft rotation, the rotor will slowly start touching the stator (In this condition, you can feel much more vibrations in the motor), which can lead to short circuit and burning of windings.

The scheduled maintenance of motor should be carried out in such a way that the motor does not reach this stage. Thus, proper overhauling of the motor is of great importance.

Before overhauling the motor, rotor running hours should be calculated, along with the lifetime of the bearing (running hours). The bearing must be renewed if required. In the motor, bearings are most susceptible to damages from friction during transmission.

How To Do Motor Overhauling?

Insulation test:

Checking the insulation of the stator winding is very important before and after the overhaul procedure. Multimeter is used for this purpose, with its one probe connected to the winding and other to the earth with switch selected in the resistance knob.

Dismantling:

Note: Before dismantling any part of the motor or motor connection, marking of both motor housing and connection wires is very important. This will ensure that the boxing back procedure is smooth and there is no mismatch of parts. Also check the direction of the motor rotation before stopping the motor for overhauling.

Before overhauling the motor, pre-planning of removing and fixing back the motor safely in place must be discussed and implemented (depends on place where it’s fixed and also on the size of the motor) otherwise the load side (for e.g. Pump connected to motor) will be damaged by the motor shaft. The motor can be connected to the load as vertically coupled load and horizontally coupled load.

Horizontally coupled having two types:

1. Hinge mounted (Must be done very carefully)
2. Base mounted

Dismantling can be done in two ways:

a. In place (On board ship, it is mostly applicable for very big vertically coupled motor to load)

• Removing the motor from the place by chain block
•  Remove the coupling and key
•  Keep the motor in place and fix the nuts
•  Open the motor from top (cooling fan side)
•  Take out the rotor by chain block, take out the stator winding separately

b.  Out place

•     Take out the motor from the place and keep it in a horizontal position
•     Open the motor from any one side
•     If it’s a small motor take out the rotor
•     If it’s a huge motor keep the rotor inside and open the bearings using a good bearing puller

After any one of the above two processes are completed, perform the following procedure:

1. Removal of Bearing Housing Cover:

While removing the bearing housing cover, note that some motors will be having inner bearing cover tightened with nut bolts. Remove it carefully.

In other constructions the bearing housing cover is locked with bearing by a circle clip. Whenever removing the housing cover on both sides (Driving End & Non Driving End) make sure proper care is taken while handling.

2. Removal of Bearing or Coupling:

Use a suitable puller (depends on the size of the bearing or coupling); mostly use the 3 arm puller as it has a good pulling strength.

– First use the puller by barely applying any pressure and try to take out the bearing or coupling,

• If it’s not coming out even after enough load, use a pipe and extend the tightening spanner and try to remove the bearing
• If the bearing is still stuck at the original position, heat the bearing or coupling up to 100 deg. C while it’s locked with the puller and apply little pressure
• If the bearing or coupling is not coming out with the above tricks, the last method is to apply the load on puller through hydraulic jack along with heating
• After opening the stator cover, thoroughly inspect the inside condition of the stator. If there is little damage in rotor, repair it
• If the insulation of the motor is less, clean the windings by an evaporative type cleaner and give sometime to let it dry. Apply insulation coating and heat the winding around 40 deg. C to 50 deg. C by means of powerful halogen lamps
• Clean both side bearing housing covers, cooling fan, body of the motor and protection cover of the motor with electro clean or suitable chemical

3. Insertion of bearings:

Clean the shaft on both ends and heat the new bearing up to 70 deg. C to avoid tight insertion of the bearing in the shaft. Do this for both sides.

Wait for 20 minutes, let the bearing cool down, and after that insert the bearing housing cover from one side.

4. Box back the motor:

Before boxing up the motor, do the insulation test again to compare with previous values. If the values are on higher side, start boxing back, otherwise heat up the winding for some more time with Halogen light.

• Box up to be done as per the markings
• Take up the rotor with one side cover (If bearing locking nut were there in one of the sides, prefer that to be the first to assemble) and push it inside the stator
• Lock with one side nut bolts, slowly insert the other side cover, do the hammering slowly by wooden hammer, insert and lock with nut and bolts, and the rotor will now apply load on the bearing
• Gently tighten the bolts using opposite tightening method. Insert the cooling fan and protection cover, and once again verify the tightness of the bolts

Fix in place the motor as per the marking and give the connections accordingly.

Try out and check the Amperage. Compare with rated amperage and before overhaul amperage.

Note: Check the direction of rotation after overhauling. If it indicates opposite direction, it means the connection done is wrong.

Are we missing anything important? Let us know in the comments below.

How to Overhaul Motors on Ships? appeared first on Marine Insight - The Maritime Industry Guide

A ship is like a floating city with all the privileges enjoyed by any normal land city. Just like a conventional city, the ship also requires all the basic amenities to sustain life on board; the chief among them is power or electricity. In this article we will learn as to how power is generated and supplied on board a ship.

Power generation On board

Shipboard power is generated using a prime mover and an alternator working together. For this an alternating current generator is used on board. The generator works on the principle that when a magnetic field around a conductor varies, a current is induced in the conductor.

The generator consists of a stationary set of conductors wound in coils on an iron core. This is known as the stator. A rotating magnet called the rotor turns inside this stator producing magnetic field. This field cuts across the conductor, generating an induced EMF or electro-magnetic force as the mechanical input causes the rotor to turn.

The magnetic field is generated by induction (in a brushless alternator) and by a rotor winding energized by DC current through slip rings and brushes. Few points to be noted about power on board are :

• AC, 3 phase power is preferred over DC as it gives more power for the  same size.
• 3 phases is preferred over single phase as it draws more power and in the event of failure of one phase, other 2 can still work.

Power Distribution on board

The Power Distributed on board a ship needs to be supplied efficiently throughout the ship. For this the power distribution system of the ship is used.

A shipboard distribution system consists of different component for distribution and safe operation of the system. They are:

• Ship Generator consisting of prime mover and alternator
  Main switch board which is a metal enclosure taking power from the diesel generator and supplying it to different machinery.
• Bus Bars which acts as a carrier and allow transfer of load from one point to another. Circuit breakers which act as a switch and in unsafe condition can be tripped to avoid breakdown and accidents. Fuses as safety device for machinery.
• Transformers to step up or step down the voltage. When supply is to be given to the lighting system a step down transformer is used in the distribution system.
• In a power distribution system, the voltage at which the system works is usually 440v.
• There are some large installations where the voltage is as high as 6600v.
• Power is supplied through circuit breakers to large auxiliary machinery at high voltage.
• For smaller supply fuse and miniature circuit breakers are used.
• The distribution system is three wires and can be neutrally insulated or earthed.
• Insulated system is more preferred as compare to earthed system because during an earth fault essential machinery such as steering gear can be lost.

Emergency Power

In case of the failure of the main power generation system on the ship, an emergency power system or a standby system is also present. The emergency power supply ensures that the essential machinery and system continues to operate the ship.

Emergency power can be supplied by batteries or an emergency generator or even both systems can be used.

Rating of the emergency power supply should be made in such a way that it provides supply to the essential systems of the ship such as

a)     Steering gear system

b)    Emergency bilge and fire p/p

c)     Watertight doors.

d)    Fire fighting system.

e)     Ships navigation lights and emergency lights.

f)      Communication and alarm system.

Emergency generator is normally located outside the machinery space of the ship. This is done mainly to avoid those emergency situations wherein access to the engine room is not possible. A switch board in the emergency generator room supplies power to different essential machinery.

You may also like to read – What is Marine Electricity And How It is Generated?

Reference: Introduction to marine engineering by D.A Taylor

How is Power Generated and Supplied on a Ship? appeared first on Marine Insight - The Maritime Industry Guide

We all know about the voltages used on board a ship. It is usually a 3phase, 60Hz, 440 Volts supply being generated and distributed on board. Every day the owners and designers aim for bigger ships for more profitability. As the ship size increases, there is a need to install more powerful engines and other machineries.

This increase in size of machineries and other equipment demands more electrical power and thus it is required to use higher voltages on board a ship.

Any Voltage used on board a ship if less than 1kV (1000 V) then it is called as LV (Low Voltage) system and any voltage above 1kV is termed as High Voltage.

Typical Marine HV systems operate usually at 3.3kV or 6.6kV. Passenger Liners like QE2 operate at 10kV.

Why High Voltage?

Let us assume a ship generating 8MW of power at 440V, from 4 diesel generating sets of 2MW, 0.8 power factors each.

Each generator feeder cable and circuit breaker has to handle a full-load current of:

I = 2 * 10⁶/ (√3 * 440 * 0.8)

I = 3280.4 Amps i.e. Approximately 3300 Amps.

The protection devices like circuit breaker should be rated at approximately 90kA for each feeder cable.

Let us now calculate the same if the generated voltage is 6600Volts.

I = 2 * 10⁶ / (√3 * 6600 * 0.8)

I = 218.69 Amps, Approximately 220 Amps. Thus the protection devices can be rated as low as   9 k Amps.

Also Power Loss = I² * r.

Where I is the current carried by the conductor,

R is the resistance of the conductor.

Thus power loss varies square of the current carried by the conductor. If the supply voltage is 440V, then the current carried by the conductor is 0.002P, and if the voltage is raised to 6600V, then the current carried for the same power is (1.515 *( 10^-4)) * P

Thus it implies that the power loss is reduced by a greater extent if the voltage is stepped up. Thus it is always efficient to transmit power at a higher voltage.

Conversely, the power loss can be reduced by reducing the resistance of the conductor.

r = ρ * l/a.

Thus by increasing the cross-sectional area of the conductor (diameter), the resistance of the conductor can be reduced and thus the power loss. But this involves huge increase in cost and heavy cables with supports. Thus this idea was not used to reduce the power loss during transmission and utilization.

Also a motor (let us assume a bow thruster), may be of a smaller size if it designed to operate on 6600 Volts. For the same power, the motor would be of a smaller size if it is designed for 6600Volts when compared to 440Volts.

Thus these are the major reasons why recent ships have shifted towards high voltage systems.

You may also like to read – What is Marine Electricity And How It is Generated?

Reasons for Using High Voltage Systems On board Ships appeared first on Marine Insight - The Maritime Industry Guide

Nowadays, many reputed shipping companies do not provide electrical officers on board ships. Companies now rely on marine engineers to tackle electrical jobs and problems related to them.

Few important reasons for this trend are the ongoing cost-cutting process and also the minimum manning does not specifically include a requirement of an electrical officer.

Moreover, electrical is one of the major subjects in the syllabus of marine engineering (It mainly includes advance, operational and fault finding topics).

Download eBook: Maintenance and troubleshooting of Marine Electrical Systems

Marine engineers are expected to handle electrical-related issues as part of their on board duties. Though several electrical jobs are to be carried out on board ship, there are a few important ones that need special attention.

Following are the most common electrical problems and jobs, which marine engineers must know about:

1. Operation of various electrical instruments: Any kind of electrical operation or maintenance job is to be carried out with the assistance of several other electrical instrument and tools such as multimeter, megger, clamp meter etc. A marine engineer must know the correct operating procedures to operate all these instruments and should also know how to interpret the readings.

2. Starter panel routine: The starter panel of every electrical system comprises of contacts which need regular maintenance for burnouts, breakage, deposits accumulation etc. The maintenance of the starter panel is a part of the planned maintenance job and all safety measures must be taken before performing the same. Marine engineers must know the right procedure for starter panel maintenance.

3. Insulation resistance: All wires and cables in the electrical system are provided with an insulation sheath. This cover may get damaged after a period of operation. If the insulation resistance reading is at a lower side, it may lead to short circuit, earth fault and equipment damage. Marine engineers must know how to maintain insulation resistance of wires and cables.

4. Earth fault finding: One of the most common problems in an electrical system is the earth fault. Finding an earth fault is an exhaustive job which requires utmost patience. A Marine Engineer should know the methods and instruments to find out the earth fault. Read more about earth fault finding here. 

5. Motor overhauling: Electrical motors are present in abundance on ships. These motors drive several other machinery systems such as pumps, fans, purifiers etc. Maintenance of these motors is to be done as per the planned maintenance system and during the breakdown. The complete overhauling procedure of motors must be known by marine engineer including the safety procedures required. Learn more about motor overhauling here. 

6. Bus Bar overhauling: This task is normally performed in the dry dock. The bus bar of the ship carries and distributes the power generated by the ship’s generator. It is important to know the correct isolating and maintenance procedures for bus bar while the ship is at normal voyage or out of water in dry dock. Learn more about bus bar overhauling here. 

7. Battery Charging onboard: Batteries are used mainly for emergency power backup and for operating emergency LSA such as lifeboat. The charging and maintenance of the batteries have to be performed at regular interval of time and marine engineers bust be aware of this process. Learn more about battery charging here.

8. Adjusting the load sensor of mooring winch: The mooring winch is important machinery used for berthing a ship to the jetty. The immense load applied by the mooring ropes on the winch is handled in a safe limit by a load sensor. If the load exceeds the limits, the sensor will trip the mooring winch to safeguard the machine. A marine engineer must know the procedure to adjust the load sensor of a mooring winch. Learn how to adjust the load sensor of mooring winches here. 

9. Shore Connection or AMP: The green revolution has introduced cold ironing or alternate marine power for dry docks (previously used only in dry dock) and in ports (now used in many ports especially for cruise ships). As the shore power parameters are slightly different i.e. voltage, frequency etc. ship engineers must know how to correctly connect the shore power to ship supply by using a transformer or frequency converter. Learn all safety procedures for shore connection in our dry dock ebook. 

10. Engine Automation: Engine automation is an important aspect to be considered during maintenance in order to ensure the overall safety of the ship. Both main engine and ship’s generator are provided with several automation, alarms and trips. A marine engineer must know the ship automation system and troubleshooting related problems within a few days of joining the ship.

These are some of the important and most common electrical jobs marine engineers must know onboard ships. Do you know any other important point that must be added here? Let us know in the comments below.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

10 Electrical Jobs Marine Engineers Must Know On Board Ships appeared first on Marine Insight - The Maritime Industry Guide

An Amplifier or an operational amplifier (op-amp) circuit is commonly used in the automation, control and other electronic circuits for marine applications.

The applied input signal is usually a voltage or a current signal. The purpose of an amplifier is to produce an output signal larger than that of the input signal.

Use of Amplifier Circuit

As the name suggests, the purpose of an amplifier or an op-amp is to amplify or increase the input signal to produce an output signal which is much larger than that of the input, with a similar waveform as that of the input.

The main change in the output signal will be the increase in the power level. This additional power is supplied by a D.C voltage which is externally provided. The output signal is controlled by the input signal in an amplifier.

In Electronic components, which are compact, small-signal amplifiers are commonly used devices as they have the capability to raise a relatively small input signal to a larger magnitude. For example from a Sensor such as a photo device, into a much larger output signal to drive a relay, lamp or loudspeaker.

Few devices on the ship you can find amplifier circuit:

• It is used to amplify the audio signals (speaker, VHF, PA system Ship horn)
• It is used as a voltage and current regulator
• It is used as an analogue to digital converter & vice versa
• It is used as a servo amplifier in motor
• The output signal from the amplifier is supplied to a relay in a circuit
• It is used in Gyrocompass
• It is used in the Engine room, deck and other alarms
• It is used in various Sensors
• It is used in electrical protection systems

Various electronic circuits are classed as amplifiers, from Operational Amplifiers and Small Signal Amplifiers to Large Signal and Power Amplifiers.

The amplifier can be further classified depending:-

• on the size of the input signal
• on the physical configuration
• on how it processes the input signal, that is the relationship between the input signal and the current flowing in the load.

Most of the electrical and electronic circuit contains the amplifying device, such as a Transistor, Field Effect Transistor or Op-amp, which has two input terminals and two output terminals (the ground being common) with the output signal being much greater than that of the input signal as it has been “Amplified”.

Operation of Amplifier Circuit

The input of the amplifier consists of differential input voltage V+ input and V-input and this difference in the voltage is amplified to produce a large output. Therefore the op-amp equation can be given by

V o/p = [(V+)- (V-)] x A o/l

Where A o/l is open-loop gain of the amplifier.

In an op-amp, the magnitude of A o/l is huge which gives a large output even when the input differential is small.

An Operational Amplifier is a three-terminal device that consists of two high impedance inputs; one called the Inverting Input, marked with a negative or “minus” sign, ( – ) and the other one called the Non-inverting Input, marked with a positive or “plus” sign ( + ).

Ideal Amplifier

We can now specify the characteristics for a perfect amplifier from our discussion above with regards to its Gain, meaning voltage gain:

• The amplifier’s gain, ( A ) should remain constant for varying values of the input signal.
• Gain is not be affected by frequency. The same amount must amplify signals of all frequencies.
• The amplifier’s gain must not add noise to the output signal. It should remove any noise that already exists in the input signal.
• The amplifier’s gain should not be affected by changes in temperature giving excellent temperature stability.
• The gain of the amplifier must remain stable over long periods of time.

Characteristics of Ideal Op-Amp or Operational Amplifier

An “ideal: or perfect operational amplifier (Op-Amp) is a device with certain unique characteristics such as infinite open-loop gain Ao, infinite input resistance Rin, zero output resistance Rout, unlimited bandwidth 0 to ∞ and zero offsets (the output is exactly zero when the input is zero).

It has a high output gain.

It has high input and low output impedance

The bandwidth is in the very high range.

Getting ideal machinery or circuit is impossible. Energy losses in an instrument are always present, but choosing a close to the ideal amplifier will provide the best operational characteristics in the electrical/electronic circuit it is installed.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

Amplifier Circuit or Operational Amplifier (op amp) Used on Ship appeared first on Marine Insight - The Maritime Industry Guide

Alternate Maritime Power or AMP is an anti-pollution measure which helps in reducing air pollution generated from diesel generators by using shore electric power as a substitute.

AMP is used when the ship is halting at a port so that the engines of the ship (working on diesel) do not need to be used unnecessarily. This, in turn, helps in reducing the emissions from the ships by a great margin. This process is also called cold ironing.

The process of cold ironing can be explained with the help of a few simple steps:

• When the ships are being loaded or unloaded in a port or dock, alternate marine power is supplied to them
• This is done so with the help of supply cables that are plugged into an electricity supply board in the port on one end and to the ship’s power supply board on the other
• The process is called cold ironing because, in the olden days when the ship’s mainframe engines used to be rested, they used to get cold while the power was being transferred in this manner
• The process leads not just preservation of the marine ecosystem but also contributes to lesser usage of diesel and other oily power supply materials
• AMP provides power for lights, refrigerators, air-conditioners and other equipment on a ship
• The power coming from the shore can be from a separate power generation unit or from the power plant supplying power to the port city or town.

At present, there are four different variations in the AMP that is provided from the port to a ship or a tanker. The same can be listed as follows:

• 11000 Volts of AC (Alternate Current)
• 6600 Volts of AC
• 660 Volts of AC
• 440 Volts of AC

As different countries around the world are becoming more aware of the clean environment, some ports like Los Angeles Port have already taken initiatives to ensure the environmental protection by reducing air pollution.

For e.g. ships berthing at Los Angeles Port or other California ports are required to stop idling the engines (low load operation) and transfer the power source to a land base. This allows the ship to switch-off its generators, thereby giving a significant reduction in noise and air pollution.

The AMP system comprises major components such as – Cable Reel, Reel Control Centre & Pendant, Amp Connection Box, 6600v Shore Panel, Transformer, Main Switch Board, Amp Control Panel.

Let’s understand each of them below:

Cable Reel

The cable reel is a ship-mounted reel that is designed to handle electrical cables that connect the ship to a land-based power source when moored at a port. The cables act as conduits for electrical power and fibre optic communication.

Once the cables are connected, the cable reel reels up for certain seconds every few minutes (according to the design) in order to recover any slack that results from ship movements and wind by changing to automatic mode. The cable reel is grounded to the hull with the help of a grounding bolt.

Reel Control Center & Pendant

The reel control centre is an IP enclosure, which incorporates the electrical switchgear required to control the cable reel operation. A pendant controller with 4 functions acts as the operator interface, and the indicator lamps mounted on the door of the enclosure provide the feedback.

AMP Connection Box

AMP connection box is the place where shore cables coming from the other end of the cable reel are connected. They are two in number, one at port side and other at the starboard side. The box is used for changing the connection of plugs to the mooring side. Usually, the plugs maintain connection except during maintenance.

6600V Shore Panel 

This panel is a switchgear for receiving electric power from the shore. A vacuum circuit breaker (VCB) and an earthing switch (ES) for high voltage are equipped herein, along with a protection relay for high voltage.

Transformer

When AMP system is in use, the shoreside power is transformed from the high voltage to low voltage, and the power is supplied to the main switchboard (MSB).

Main Switchboard

AMP panel in the main switchboard (MSB) can operate by an automatic or manual operation to synchronise with the shore power without leading to blackout situation.

AMP Control Panel

AMP system is controlled by this panel. It has a condition monitoring function.

Fibre Optic Communication

In some AMP systems, fibre optic communication is used between shore and ship. A fibre optic cable goes along inside the cable for the purpose of communication. Clean fibre optic components are a requirement for quality connections between fibre optic equipment. Any contamination in the fibre connection can cause a communication failure. Even microscopic dust particles can cause a variety of problems for optical connections. By comparison, a typical human hair is 50 to 75 micrometres in diameter and is about 8 times larger than a dust particle. So, even though dust might not be visible, it is still present in the air and can deposit onto the connector. In addition to dust, other types of contamination must also be cleaned off the end face.

Cable Reel Overview

Cables: The cables act as conduits for electrical power and fibre optic communications. They are specifically designed for reeling purposes, having exceptional flexibility and high tensile strength. A special sheathing compound provides high resistance to the harsh marine environment.

Drum: The drum is used to store the cables. The internal diameter of the drum is selected to meet the minimum bend radius requirements of the cable and to ensure an optimal relationship between reeling torque and cable tension. The external diameter of the drum is selected to ensure that the full cable length can be accommodated.

Guide: The guide acts to provide a relatively frictionless path for the cables between the drum and the side of the ship. It consists of a number of rollers arranged in a radius that is greater than the minimum allowable bend radius of the cable.

Collectors: The collectors facilitate the transmission of power and data between the rotating reeling cable and the fixed machine cables.

Hydrodynamic Drive: The Hydrodynamic drive is a specially designed reduction gearbox that incorporates an oil-immersed torque-regulating clutch. Torque is produced by shearing oil between two rotating metallic disks. The amount of pressure acting at the interface, and therefore the torque output, can be easily adjusted over a large range.

The concept of AMP has come a long way. In the initial days, cold ironing was used just as a recharging accessory for the tankers. However, seeing that the usage has widened and grown so much in these past few years, it can be assumed and hoped that alternate marine power will become a tool far more vital and necessary than what it is today.

Ship/Shore Changeover Procedure

There are two methods of changeover – an automatic change and a manual change.

As for an automatic change, a synchronization and load shift are performed automatically. A manual change can perform a synchronization and load shift by manual operation. Automatic and manual synchronous change is performed by running of only one generator. It is necessary to decrease the load and obtain changeover at minimum load.

AMP Connection Procedure

• First, confirm that the generator is on the minimum load possible and voltage is around 440V. To lower the cable guide, first connect the operation remote to the reel, after which, the reel is ready for operation. The Power On indicator lamp on the Reel control centre will light up.
• Press up and hoist up the cables from their parking position. The reel will stop rotating automatically when the upper limit is reached.
• Direct the cables to the cable reel guide and prepare it for lowering by pressing down button.
• Press down button and lower the cables, keep a check there is no snag, twist or turn. Keep lowering the cables until it reaches the port personnel on the jetty.
• The port personnel must pull the cables towards the connection box while the cable is still unwound, then remove the protective caps on the end of the cables and connect them to the shore terminal. The cable plugs should be connected according to colour coding and should be connected correctly.
• Once the cables are connected, change the selector switch to automatic mode. The reel should then automatically operate in order to recover any slack that results from ship movements and wind.
• You will have to confirm with shore personnel whether fibre optic communication will be used or not. If yes, then you will have to turn on fibre optic switch inside main switch mode. If no, then communication can be done via VHF or Phone.
• Try out the emergency stop on AMP control panel. The pilot ready lamp should turn off confirming positive working of the emergency stop.
• Try out emergency stop on cable reel control panel. The pilot lamp should turn off confirming positive working of the emergency stop. Reset from the panel.
• After completion of all tests, you are ready to turn on the VCB and close the breaker. Confirm with the shore personnel that VCB can be closed and upon confirmation, close the VCB
• After closing the VCB, you are ready for synchronisation. This can be done automatically or manually. First, you need to check shore receiving parameters to check if they are all correct and in range. For automatic synchronisation, press synchronise on the AMP control panel and the shore power will synchronise with ship’s generator power. For manual synchronisation, you can synchronise with synchroscope method or three bulb method
• Once shore power has synchronised with the ship’s generator power, you can offload the ship’s generator so that all the load can be taken by shore power. Once the generator is offloaded and the breaker is open, the ship can be said to be running on alternate maritime power.

The shore charges for the power it supplies in KWH. So, it is always advisable to have minimum load possible when on alternate maritime power so that costs don’t increase significantly.

AMP Disconnection Procedure

• Disconnection procedure is reverse of connection procedure. You have to take shore supply offload and ship’s generator on-load by following these steps
• Start ship’s diesel generator and take it on-load by synchronising it with shore power automatically or manually. After the generator is on-load successfully, offload the shore power by opening the VCB. Open the VCB only after confirming with shore personnel.
• Once the AMP VCB is open, the ship is running on ship’s generator and no more cold ironing. Cables should be made ready for disconnection.
• Change the selector switch to manual mode and press the DOWN button to slacken the cables
• The port personnel must disconnect the plugs & sockets and re-fit the covers.
• Press the UP button to retrieve the cable. Avoid dragging the plug protection covers along the jetty, it is preferable that these are manually handled in order to reduce wear.
• Continue pressing the UP button until the upper limit is reached. With the assistance of another person, press the down button and guide the plugs into the parking zone. Turn off reel control centre.

However, even as cold ironing has a lot of advantages, there are quite a few disadvantages to the process. The crucial disadvantages can be explained as follows:

• Problems pertaining to cost. The consumption of electricity can be enormous owing to the size of the ships and tankers. This factor is the primary negative contributor to AMP
• Every port and harbour where such ships halt for the loading and offloading of cargo and thereby for the cold ironing process will require a huge investment to set up the equipment for AMP
• Even certain ships are not compatible and suitable for the process of alternate marine power. The cost of equipping these tankers with the right kind of AMP gadget will also require an enormous investment
• The reduction in pollution occurs only when the ship is stationary. When the ship is actually in the water, then because of the usage of conventional engines, pollution will still spread in the marine atmosphere

You may also like to read – What is Marine Electricity And How It is Generated?

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

What is Alternate Marine Power (AMP) or Cold Ironing? appeared first on Marine Insight - The Maritime Industry Guide

Marine Electricity or Marine electrical power is a vital part of a ship’s operation. Without marine electricity, ships would not be able to run any of the machinery and cannot perform their core purpose of sailing from one place to another.

We cannot define the term “Marine Electricity” as a whole. To understand its meaning, first, we need to understand them separately.

Marine – Here, the term “marine” refers to ships, ports, drydocks, and other structures which cater to the shipping of cargo by sea.

Electricity – It is a type of energy resulting from the existence of charged particles (such as electrons or protons), either statically as an aggregation of charge or strong as flowing current.

The electricity which is produced, supplied and distributed onboard ship, port, drydock, shipyard for running or repair of the cargo and passenger ships is referred to as Marine electricity.

Marine Electricity Generation 

Marine electricity generation can be done onboard ships by diesel, shaft or steam-driven generators.

For ports, shipyards, and structures located inland, marine electricity is utilized from the electricity supply of the land-based power generation plants.

Unlike land, the ship’s generator has insulated neutral points i.e. its neutral is not grounded or connected to the ship’s hull. This is done to ensure all the essential machinery are up and running even if there is an earth fault.

The ships plying in the international waters generally have 3 phase D.C. supply with 440v insulated neutral system. Ships like RORO, passenger etc. having large electrical load requirements are installed with high voltage operating gensets in the range of 3KV to 11KV.

On land, the frequency of the power supplied can be 50 or 60 Hz depending on different parts of the world. On ships, 60hz frequency is adopted as standard practice which helps hundreds of motors on a ship run at higher speed even if they are of smaller size.

The supply which is at 440v is stepped down using a transformer to 220V or 110V for lights and low power signal equipment.
All the electrical equipment onboard ships are similar to land however, they are upgraded to withstand the rigorous atmosphere of the sea and moving ship to withstand humid surroundings, high temperatures, salty and corrosive atmosphere, vibration, etc.

Parts of the Marine Electricity System

Different parts of the marine electricity system –

The electrical onboard ships can be divided into five specific systems:

• Generator system
• Main Switchboard System
• Emergency Switchboard System
• Distribution system

Generator System

The generator system consists of an alternator and driver for the alternator which can be a diesel-driven or steam-driven engine.

Many ships are equipped with shaft generator where the rotation of the main engine of the ship is used to operate the alternator and generate additional electricity.

The Power generated by these marine generators is transported to the Main switchboard using Busbars. There are no electrical wire connections inside the main and emergency switchboards on ships for connecting Power supply from generators to these switchboards. All high voltage and high current systems are connected by bus bars.

Main Switchboard System

The main switchboard is considered as the distribution hub of the ship’s electrical system taking power from the power generator and distributing it to the power consumer spread all over the ship. It provides a power supply to all important ships machinery with 440V.

A part of the main switchboard is provided with a 220V supply via a stepdown transformer. It includes bridge equipment, navigation lights, radio communication equipment, etc. The power from the auxiliary switchboard is used to charge the battery which is used for emergency lights.

Read more about the maintenance of busbar and main switchboard

Emergency Switchboard System

An emergency generator is required to be operational at all times once the main generator fails. This emergency generator will start automatically and provide power to the emergency switchboard.

All the emergency equipment supply is connected to the emergency switchboard. The emergency switchboard is also divided into two sections – 440V and 220V, providing supply to appropriate machinery and equipment.

Read more – Maintenance Of Emergency Generators

Distribution system

The Distribution system comes after the switchboard and consists of the following

Distribution boxes: These boxes are enclosed and made up of metal to supply power to localized parts of the ship’s machinery.

Motor starter boxes: There are hundreds of motor operating several mechanical machinery onboard ship. Each group of motors is provided with a motor starter boxes containing their “On & OFF” switch along with safety devices. Local gauges for amperage and temperature are fitted on the starter panel.

Shore connection boxes: When the ship is in a port with emission control requirements or during the dry-docking process where the ship generator cannot run, shore power is taken for running ship machinery. Shore panel is provided which is usually located near accommodation entry or near the bunker station to easily accept shore supply cable;

Know how to take shore supply for ship

Lighting distribution panel

The lighting distribution panel supplies power to lighting systems, accommodation systems, small heating appliances, circuits, and motors of 1/4 HP or less.

Emergency switch-off panel: For safeguard of ship machinery and personnel, various Emergency switch Off Panels are provided at different locations for shutting down machinery and equipment in an emergency situation.

The main aim of installing a distribution system is to have an operational, alarm, and safety consol for individual or group of machinery. Power is supplied through circuit breakers to large auxiliary machinery at high voltage. For smaller supply fuse and miniature circuit breakers are used.

Marine generator working principle

The generator works on the principle that when a magnetic field around a conductor varies, a current is induced in the conductor.

The generator consists of a stationary set of conductors wound in coils on an iron core. This is known as the stator. A rotating magnet called the rotor turns inside this stator producing a magnetic field. This field cuts across the conductor, generating an induced EMF or electro-magnetic force as the mechanical input causes the rotor to turn.

The magnetic field is generated by induction (in a brushless alternator) and by a rotor winding energized by DC current through slip rings and brushes.

The power generation and transmission process is explained in this article.

Safety of marine electricity system

The Safety of marine electrical systems includes safekeeping of personal from electrical shock and damage to the machinery due to electrical malfunction.

For safety against electrical shock, check our article on – How to Minimize the Risks of an Electrical Shock on a Ship?

For machinery safety, depending on the size and power rating of the equipment, a relay, circuit breaker or fuse can be used which prevents the electrical equipment from overcurrent or overheating.

Temperature gauges, RPM of the motor, direction indicator, Amperage meter, etc. are different equipment used locally to monitor the performance of the electrical machinery or equipment and to understand the general health of the machinery.

Read more on Main Safety Devices for Main Switch Board on Ship?

Books On Marine Electrical System 

Understanding the design, operation and troubleshooting of marine electrical systems is important for all maritime professionals. Marine electricity is often neglected by maritime professionals during their careers. Mentioned below are a list of some of the best ebooks on marine electrical system written by expert authors.

Maintenance and troubleshooting of marine electrical systems – volume 1

A popular bestseller on the marine electrical subject, this ebook is exclusively written for deck officers, marine engineers and electrical officers. This is a must-have for all.  Check out volume 2 of the same ebook here. 

Marine Control Technology 

An extensive guide on marine control technology, this ebook now in its 4th edition, consists of information on the latest advances in the shipping industry.

Marine Electrical Technology

This is the ultimate guide for everything related to marine electrical technology. This ebook is imperative for maritime professionals of all levels in the merchant navy.

Testing of Electronic Components on ships and land

One of the important aspects of troubleshooting electrical faults is to locate a suspected component and figure out if it is faulty or not. This guide will help you with understanding the testing of electronic components.

Marine High Voltage Technology 

In accordance with STCW 2010 Manila Amendments, this ebook offers all information related to marine high voltage equipment and technology.

Competency In Marine Electrical Technology 

If you are applying and preparing for a competency certificate, then this guide will provide you with all the information that is required to qualify.

ETO & MEO Class IV

This book comprises of 3100 questions and answers on marine electrotechnology, electrical, electronics and control engineering.

Applied Marine Control And Automation

If you want to learn about marine automation, control engineering, and instrumentation then this is the right ebook for you.

The Explosion Protection Equipment Guide For Mariners 

Do you want to know how to work with electrical equipment in hazardous areas onboard all types of ships to ensure utmost safety? Then this is the right guide for you.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight.

What is Marine Electricity And How It is Generated? appeared first on Marine Insight - The Maritime Industry Guide

Dozens of motors are used on board ships for a variety of purposes in both deck and engine department. Each of this motors has its dedicated starter panel, which is used for the switching purpose i.e. On and Off operation. Like any other machinery system, these motor starter panel also needs regular maintenance to ensure smooth motor operation. A general starter panel maintenance routine is discussed below:

What is Starter Panel Routines?

Motor starter panel routines includes inspection and maintenance of motor’s starter panel.

1. Starter panel routines mean inspection and cleaning of contactor’s (the switch inside the starter panel box controlling the on and off of the motors) contacts.
2. Checking of connections in the starter panel
3. Cleaning of the complete starter panel
4. Checks in the terminal box on the motor for loose connections
5. Visual inspection of overall starter panel

Why Starter Panel Routines and Maintenance are Important?

Every time we switch on the motor, the contacts in the panel get energized as electricity flows through the contacts (high current flows during starting). At the time of on/off of the switch, a spark is generated in the contacts for a fraction of seconds. In case of poor contacts, this spark will damage the same, leading to pitting/scoring marks in the contacts along with carbon deposits on the contact surface.

 Safety Measures to be Followed While Starting Motor Starter Panel Routines

1. Switch off the main power supply from the circuit breaker
2. Take out the main fuses in the starter panel, and if required control fuses as well
3. Put the lock out tag
4. Inform the engineer who is in charge of that particular machinery

How to Carry Out Motor Starter Panel Maintenance?

1. Open the motor starter panel and the contactors. This would a need special ‘T’ type key, which is found with the electrical officer. The panel can be opened when the breaker is switched off.
2. Take out the moving contacts and the arc huts. Keep a very fine emery paper, good evaporative type contact cleaner, and a clean cloth for cleaning and maintenance purpose.
3. Mark the moving contacts from where it was removed; clean the fixed and moving contacts, and the arc huts.
4. Fix the contacts as per the markings and check for any lose connections inside the panel.
5. By visual inspection we can identify the contact’s condition. Take out the contact, clean it by a smooth cloth or a very fine emery paper and measure the contact’s width by a Vernier caliper at 3 different places. Note down the values.
6. Simultaneously take a same type of new contact, measures and note down the width values measured in 3 different places. Now compare the values to find out the actual contacts condition.
7. If difference between the values is bigger, replace the contact with a new one (same type).
8. Also make sure that the measured value of a single contact must be same on both sides in both moving and fixed type contacts, otherwise there is a high possibility of sparks generation.

Important Points 

If cleaning of deposited carbon is not carried out at regular intervals, it can lead to two main issues:

1. A poor contact – which will increase the spark amount and frequency
2. Increase of fire hazard – The deposited carbon will act as fuel for fire

Checking for Loose Connections

Inside the motor starter panels, check should me carried out for loose connections to avoid short circuit, spark or accidents.

How to Check for Loose Connections?

1. Tighten the loose screws using a Screwdriver, if found any
2. Using your hand, try to pull out the wires slowly. If any wire comes out completely or more than it should, take it out and reconnect
3. Check the insulation of the connected wires, as because of aging and sparks there is a possibility of damage to the wires

Cleaning of the Starter Panel

• The motor starter panel should always be maintained clean to reduce fire hazards
• Clean the whole starter panel by a wet cloth and use brushes where hands cannot reach
• A vacuum cleaner can be used to remove dust

Checking the terminal box of the motor

Motor is a dynamic machine, and thus there will always be vibrations. This leads to loose connection in the terminal box of the motor.

1. Open the terminal box of the motor by loosening the nuts
2. Check the tightness of the connection by shaking the wires and use the correct size spanner to tighten the connections

If there are any loose connections, it will lead to sparks in the terminal box causing fire in the motor.

Short circuit is also possible because of a loose connection.

After the maintenance is done on the motor starter panel

1. Remove the lock out tag
2. Insert the main and control fuses in the starter panel
3. Switch on the main power supply from the circuit breaker
4. Inform the Engineer who is in charge of that particular machinery
5. Start the machine and check the starter panel if there is any abnormal sound

Motor Starter Panel on Ships : Maintenance and Routines appeared first on Marine Insight - The Maritime Industry Guide

The most important factor for the staff working onboard ships (or in any other industry) is – the personal safety and the safety features incorporated in machinery and systems.

Electrical components and mechanical systems present in the engine room are mainly maintained by the electrical officer.

The routine maintenance for electrical machinery involves checking of insulation resistance, which is done by an instrument called “ohmmeter”.

The insulation resistance test is done to ensure the integrity, i.e. to resist the current flow outside the equipment, and keeping it within the dedicated parts.

The measured “IR” (Insulation resistance) can be of a wire, cable or motor/generator windings. In simple terms, every electrical insulation should have the opposite characteristic as the conductor.

For e.g., in the pump casing and pipes in a water carrying system acts as the insulation, which prevents the leakage of water. Similarly, in an electrical wiring system, the wire insulation prevents the leakage of current which is carried in a copper wire.

Insulation Resistance – Importance And Causes of Decrease 

Insulation resistance (I.R) is a critical parameter as it’s directly related to personal safety, the safety of machinery and power reliability.

The I.R value of electric devise changes with ageing, mechanical and electrical stresses, temperature, contamination, atmosphere, humidity etc.

It is therefore important for the engineers and electrical officers to identify this detection to avoid any accidents on board ships because of electric shock.

Another common cause of the decrease in the value of insulation resistance is the ingress of water. If the electrical equipment is wet due to freshwater, it can directly be dried out for checking the IR values.

However, in the case of seawater ingress, the first step is to wash it with fresh water to remove the salt deposits which will cause corrosion of metal parts and insulating surface.

Remove oil and grease from such equipment using a suitable solvent.

Any wet equipment on the ship is susceptible to voltage breakdown. Therefore, when using ohmmeter at the drying out stage, low voltage ohmmeter insulation tester (100 or 250 VDC) to be used.

If low voltage ohmmeter is not available, using slow cranking in a mechanical type 500 V ohmmeter can be done to achieve the results.

Sometimes, electrical ohmmeter is also provided with a test range in kilohms (kW). This test range measurement is the ideal initial check to be made on flooded equipment.

Why is Ohmmeter Testing Done?

As mentioned earlier, the insulation resistance of an electrical system degrades over time because of several factors. The insulation resistance needs to be tested to check the insulation quality (punctures in insulation) of the electrical system and to avoid any major or minor electrical shocks to operators.

Thus ohmmeter testing is carried out to find out information on leaking current and the areas where insulation has deteriorated because of excessive moisture and dirt in the electrical circuits.

Any specific circuit found faulty is then isolated and replaced/repaired to avoid any further problems and ensure the safety of the crew.

Use of Ohmmeter on a Ship (And in other industries)

The Ohmmeter is widely and frequently used by the ship’s officer for the following jobs:

• Testing an Earth/Ground connection
• Battery Testing
• Relay Testing
• Watthour Meter Testing
• Oil Testing
• Transformer Testing
• Circuit Breaker Testing
• Cable Fault Testing
• Power Quality Analysis
• Power Factor Testing
• Low Resistance Testing
• Motor winding testing
• Alternator winding testing

There is no fire hazard related to Ohmmeter insulation tester when used in a normal atmosphere. However, when using the instrument for testing equipment located in inflammable or hazardous atmospheres, it may lead to an explosion due to the spark created, when using the instrument.

Do not use the ohmmeter test equipment in an explosive atmosphere (such as the deck of an oil tanker ship).

Types Of Ohmmeter

Ohmmeter is a portable instrument which is used to measure the insulation resistance of the electrical machinery or system. It can be battery operated or mechanically operated (hand crank dc generator) and gives a direct reading in ohms. For this reason, it is also called as ohm meter.

Onboard ship, different systems are present with large voltage ratings and therefore ohmmeter comes in the range of 50, 500, 1000, 2500, and 5000 V, thereby making ohmmeter meter suitable for applications on normal voltage equipment to more demanding high-voltage applications.

The categories of an ohmmeter test equipment can be divided into two:

• Electronic Type (Battery Operated)
• Manual Type (Hand Operated)

There are other types of ohmmeter available in the market, which is operated by an attached motor requiring an external power source for rotation.

This motor then rotates the generator fitted in the ohmmeter. As the overall size of such meter increases due to the addition of a motor, and their dependency on a power source, they are not much preferred for use on ships.

Electronic Type Ohmmeter:

The electronic type ohmmeter, also known as electrical ohmmeter, is compact of all types and uses a battery for operation. The important parts of this ohmmeter test equipment are:

Digital Display:- To show the insulation resistance value in digital form

Testing Wires:- Two-wire leads for connecting ohmmeter with an electrical external system for testing the later.

Selection Switches:- Different parameter ranges are provided on the meter, which can be selected by using the selection switches.

Indicators:- Different indicators are incorporated into the instrument to give a visual and audible indication when the instrument is ON, for a warning, parameter status etc.

The construction and parts of electrical ohmmeter will vary depending upon the manufacturer, however, the basic construction and operation remain the same.

Advantages Of Electronic Ohmmeter

1. Has a very high measurement accuracy
2. Easy to operate for one person
3. The digital display makes it easy to read the IR value
4. Robust and safe to use
5. Less maintenance as compare to other types
6. Works well in congested spaces
7. Handy and compact to carry
8. Less time-consuming operation

Disadvantages of Electronic Ohmmeter

• Requires an external source of energy to energize i.e. Dry cell
• High initial cost

Handheld Type Ohmmeter:

The handheld type ohmmeter is still used on the ship as it provides service without the need for battery and external power source. The main parts of such ohmmeter testing unit comprise of:

Display:- An Analog display is provided, which is a pointer and a scale, to show the IR value recording.

Hand Crank: As this a manually operated ohmmeter, a hand crank is provided which can be rotated to generate the required voltage, which runs through the electrical system for an insulation resistance test.

Wire Leads:- Two-wire leads are provided which can be connected to the electrical system which needs to be checked.

Advantages of Hand Operated Ohmmeter

• No external source required to operate
• An excellent choice for emergency use
• Cheaper than the electrical ohmmeter

Disadvantages of Hand Operated Ohmmeter

• At least 2 ship staff are required for operating handheld ohmmeter. one for rotating the crank and other to connect wire leads to test the IR of the equipment
• Not highly accurate as electronic ohmmeter as the value will vary with the rotation of the crank.
• It needs a stable place to operate and record the IR value, which is a little difficult to find at work sites.
• Unstable placement of tester may impact the result of IR value.
• Provides an analogue display result.
• Require very high care and safety during the use of the same.
• Time-consuming operation

Principle Of Ohmmeter Operation

The ohmmeter works on the principle of the moving coil instrument, which states then when a conductor carrying current is placed in a magnetic field, a force is exerted on the conductor.

As seen in the figure below, when the current-carrying conductor comes in the magnetic field of the permanent magnet, a defecting torque is produced, which moves the pointer in the scale.

Construction Of Ohmmeter

The important construction features of Ohmmeter consist of following parts:

1. Control and Deflecting coil: They are normally mounted at a right angle to each other and connected parallel to the generator. The polarities are such that the torque produced by them is in the opposite direction
2. Permanent Magnet: Permanent magnet with north and south poles to produce a magnetic effect for deflection of the pointer.
3. Pointer and scale: A pointer is attached to the coils and end of the pointer float on a scale which is in the range from “zero” to “infinity”. The unit for this is “ohms”.
4. D.C generator or battery connection: Testing voltage is supplied by hand-operated D.C generator for manual operated Ohmmeter and a battery and electronic voltage charger for automatic type Ohmmeter.
5. Pressure coil and current coil: Provided for preventing damage to the instrument in case of low external source resistance.

Working Of Ohmmeter

The voltage for testing is supplied by a hand generator incorporated in the instrument or by battery or electronic voltage charger. It is usually 250V or 500V and is smaller in size.

• A test volt of 500V D.C is suitable for testing ship’s equipment operating at 440V A.C. Test voltage of 1000V to 5000V is used onboard for high voltage system onboard.
• The current-carrying coil (deflecting coil) is connected in series and carries the current taken by the circuit under test. The pressure coil (control coil) is connected across the circuit.
• Current limiting resistor – CCR and PCR are connected in series with pressure and current coil to prevent damage in case of low resistance in the external source.
• In hand generator, the armature is moving in the field of a permanent magnet or vice versa, to generate a test voltage by electromagnetic induction effect.
• With an increase of potential voltage across the external circuit, the deflection of the pointer increases; and with an increase of current, the deflection of pointer decrease so the resultant torque on the movement is directly proportional to the potential difference and inversely proportional to the resistance.
• When the external circuit is open, the torque due to voltage coil will be maximum and the pointer will read “infinity”. When there is short circuit the pointer will read “0”.

General Inspection of Ohmmeter

–    Check for loose connections, defective insulation, and cleanliness

–    Check meter stop and pointer for damage

–    Check the carrying case for corrosion, foam fungus etc.

–    Check for easy cranking arrangement for mechanical ohmmeter

–    Check the foam rubber lining if fitted

–    Check the battery level for digital ohmmeter

–    Check all indicators are working fine

General Maintenance of Ohmmeter:

• Digital multimeter is provided with a fuse. Replace it if the ohmmeter is not working
• Clean the surface from dust, dirt, grease fungus etc.
• Remove dust or dirt from terminals with a soft brush
• Clean the display using a soft cloth
• Clean the cables, meter glass, and the exterior surface with a clean, soft cloth. Dampen the cloth with water if required

What Things to Record After an Ohmmeter Test?

When performing an ohmmeter test on machinery or equipment, the following things to be recorded:

• Name and location of the equipment/ wiring
• The date on which the test is performed
• The Insulation Resistance values of test results along with time
• Range, voltage, and serial number of the ohmmeter instrument used
• The temperature of the apparatus during the time of the IR test
• When doing IR test of bigger machines such as alternator, transformer etc. wet and dry bulb temperatures and dew-point determinations to be noted
• Insulation resistance measurement corrected for temperature

Always remember to disconnect the machinery and equipment being tested for insulation resistance as there is a possibility of voltages being induced in apparatus under test or lines to which it is connected (because of proximity to energized high voltage equipment).

Use required PPEs such as rubber gloves etc. when connecting the wire leads to test the apparatus for performing the insulation resistance test.

Some ohmmeter may be provided with a voltage scale to ensure the line to be tested does not have any voltage for insulation testing.

You might also like to read:

• 10 Electrical Jobs Marine Engineers Must Know On Board Ships
• 10 Ways to Achieve Energy Efficiency in Ship’s Electrical System
• Electrical Propulsion System in Ships
• Single Phasing in Electrical Motors: Causes, Effects, and Protection Methods
• How to Minimize the Risks of an Electrical Shock on a Ship?

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight.

Ohmmeter – Construction and Operation Explained appeared first on Marine Insight - The Maritime Industry Guide