MEO Class 4 Function – 5 (EECEOL ) Electrical Questions With Answers
What is an Induction Motor ?
An induction motor is an Asynchronous motor in which Electric Current required to Rotor to Produce Torque, Which is obtained by Faraday’s Lay of Electromagnetic Induction.
Induction Motor Working Principle ?
An Induction Motor Works on the principle of Faraday’s Law of Electromagnetic Induction.
Faraday’ Law of Electromagnetic Induction has Two laws.
Faraday’ First Law
It states that, whenever there is a change in the magnetic field linked with a circuit, an induced e.m.f ( electromagnetic force ) is produced in it. Or, The electromagnetic induction is the phenomenon in which the electromotive force induces across the electrical conductor when it is placed in a rotating magnetic field.
Faraday’ Second law
It states that, the magnitude of induced e.m.f is equal to the rate of change of the magnetic flux linked with a closed circuit.
E.M.F = Rate of Change of Magnetic Flux.
State Working of An Induction Motor
Types of an Induction Motor
1. Single Phase motor
- Split phase
- Capacitor start
- Capacitor start capacitor run
- Shaded pole
- Slip ring
- Squirrel cage induction motor
Types of Motor
1. DC Motors
- DC shunt motor
- DC Series motor
- Compound motor
- Permanent magnet motor
2. AC Motors
- Induction Motor
- Synchronous Motor
3. Other Motors
- Universal Motor
- Brushless motor
- Servo motor
How to maintain proper temperature in the Batter room
By proper ventilation
Battery Room heating prevention
- Switch should be outside.
- Paint used should be Acid Proof.
- Intrinsic safe equipment
- Intrinsic safe lighting
And during maintenance
- Used Intrinsic safe torch
- Insulated spanner and jug
It states that, the direction of the electric current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes changes in the initial magnetic field. Or, An induced current always flow in the Direction such that it opposes the magnetic field which produce it.
All motor working principle used in Engine Room ?
1. An Induction Motor :- Faraday’Law of Electromagnetic Induction
2. Synchronous Motor :- It works on the principle of Magnetic Locking between Rotating Magnetic Field ( this field produced by 3- phase supply to the stator ) and Static magnetic field ( this field produced by D.C supply to the rotor ).
3. DC Motor :- It works on the Principle of Lorentz’ s Law.
It states that, whenever a current carrying conductor placed in a magnetic field, it experience a force.
It is an alternator, which is used to generate mechanical energy to Electrical Energy by using Two Rotor fitted end to end on same shaft and transfer electricity without brushes and slip rings.
Or, It is an alternator, which do not uses brushes and slip rings and consist of two alternator, main exciter and small exciter alternator in which excitation is done by small Exciter Alternator fitted on the same shaft of main alternator with the help of the Bridge Rectifier.
Advantages of Brushless Alternator is Less Cost and Maintenance is less due to absence of brush and slip rings.
It is a Loss in the Transformer in form of Heat produced by the electrical current flowing in the coils and the alternating magnetic field ( Flux ) in the core.
Two types of losses are :-
1. Iron/Core Loss
2. Copper Loss
1. Iron / Core Loss
It is a Loss in the form of heat due to Alternating magnetic flux in the core.
It is a fixed loss. It only depends on the Voltages.
a. ) Hysteresis Loss :- It is a Loss in the core of transformer due to magnetisation or demagnatisation of the Core.
It is Reduced by using core made up of Silicon Steel.
b. ) Eddy Loss :- It is a Loss in the core due to flow of Eddy current. Or,
It is a Loss in the core due to flow of current produced by law of Electromagnetic Induction of magnetic flux due to input supply to Transformer..
This current has no useful work and produce a loss I^2 R.
2. Copper Loss
It is a loss occur due to Ohmic Resistance of Winding of Transformer.
Copper Loss :- I^2 R.
It is a variable loss and depend on Current.
It means high rupturing capacity fuse
It is a fuse in which, fuse wire or element carry Short Circuit Heavy current for a Known Period of Time. During this time period, if the fault gets removed then it does not Blow off.
Battery Room Maintenance
Under Voltage Protection
Under Voltage Protection is a safety device fitted on all generator circuit breaker and feeder circuit breaker. It’s main function is to trip the breaker when a severe voltage drop occurs across the the circuit breaker.
Under Voltage Protection on a circuit breaker,it also prevents from circuit being closed when the generator voltage is very low or absent.
It may be magnetic or electronic which provide back-up protection to short circuit protection.
Note :- Under voltage protection is also known as under voltage relay and under Voltage trip.
Types of Starter used on Ship With Example ( on which motor used ?
2. Star Delta Starter :- Main Sea Water Pump Motor, Air Compressor Motor, Fire and GS Pump Motor, Main Fire Pump.
3. Transformer Starter :- Ballast Pump Motor.
4. Soft Starter :- Conveyor Belt
What Multimeter Measure
- Continuity Test
Electrical measuring instruments
Armature reaction and how to reduce it ?
It is the effect on the main field Flux due to flux generated by current in the armature winding.
How to dampen
- Pole stacking
- By using laminated pole
- By using interpole between main field.
Motor Protection Device
- Under Voltage Relay
- Over current and Single phase relay
- Short Circuit Relay
- Temperature sensor for Motor Insulation
Fuse and Circuit breaker cone under over over current and short circuit fault.
What is Earth fault ?
When any one of the phase touched with earthed, known as Earth fault.
A Earth fault is a fault due to break in the insulation, and conductor touched the hullor an earthed metal enclosure.
Earth fault in Motor
Earth fault in Motor when live wire of any phase get earthed.
Reason of the Earth fault
- Failure of Insulator
- Loose wire Connections of wire
How to detect an Earth fault in Motor
Check IR Test of Motor, Phase to Earth.
Insulation Resistance value between phase to earth = Infinite
How to check Continuity Test of Fuse
Major Reasons of the Electric Fire on Board
- Short Circuit
- Spreading of a solid or liquid fire.
- Overload of the conductor and may overheat, resulting in a fire.
- Loose Connection of Nut cause Spark.
- Insulation failure of wire and touched with other wire and short circuited.
- Space heater is not working due to generation of moisture get short circuit.
- Arc Chute is not working properly.
Dead Man Alarm
It is an alarm, which is used for monitoring the presence of Engineer in the Engine Room on UMS Ship.
Location of Dead Man Alarm
- Engine Room accommodation Station 1
- Engine Room accommodation Station 2
Engineer goes on the Engine Room at night for watch then he should must activate the Dead Man Alarm. It is because, he will be alone in the engine room and if he gets injured then there is no one to attend the Alarm. Alarm will ring unattended. Another alarm is fitted in the chief Engineer cabin. He recue the watch keeping engineer.
Use of space heater in alternator and motor
Alternator and motor usages space heater to prevent moisture condensation during the time, motor is not running.
It is a starter which limit the starting current by supplying a gradually increasing a.c voltage during start up.
To limit starting current, a soft starter will slowly and gradually increasing voltage applied to the motor.
In each phase, a parallel reverse SCR is used. SCR also known as Thyristors.
Advantages of soft starter w.r.t to ther starter
It allows smooth operations of power instead of sudden power supply like other starter.
What will you do, if level in the battery decrease.
We put distilled water in it.
Note :- We do not use mineral water, because it contains some impurity which damage the plate of battery.
Running Motor Maintenance
- Sound / Noise
- Heating by touching ( Temperature 🌡️)
- Foundation bolt
Reasons for Motor Overheating
- Ventilation holes blocked
- Motor running continuously
- A poor surrounding environment
- Wrong voltage supply
- Bad or jammed motor fan
- Noise to electric motor also reasons of Overheating.
Shore Supply Specifications
It is a property of material in which some amount of excitation remain in the conductor after removal of magnets. Or, Residual magnetism is defined as the amount of magnetization left behind after removing the external magnetic field from the circuit.
Steering gear Safety
Difference between slip ring and Commutator
Slip rings :-
1. It is a Electrical device, which is used for Transmission of Electrical Power and signal from stationary to rotary parts without changing the polarity of current.
2. It is Continuous
3. Example :- AC Motors
1. It is a electrical device that that Electric Power or maintain electric continuity between stationary and rotary parts by changing the polarity ( or periodically reverse the Direction of currently between rotar and external circuit ).
2. It is segmented
3. DC Motor
Physical Difference between Commutator and slip rings is slip rings is continuous ring whereas Commutator is segmented.
It is a loop of electric current induced within the conductor by changing magnetic field in the conductor according to Faraday’s of Electromagnetic Induction.
Eddy current loss is the loss in the form of heat occur due to flow of Eddy current.
Eddy Loss can be reduced by
- Laminated core
- By using thin sheet of core.
Types of Control System
Open Loop System
The Control System in which the required output does not depend on the Input or Controlling Actions.
Example :- Light, Remote, Traffic Light.
Close Loop System
The Control System in which output depends on the input or Controlling Actions etc.
Example :- AVR in alternator, Refrigeration System etc.
Air Gap in Motor or Alternator
It is a gap between moving Rotor and the Stator core.
Or, It refers to a plastic gap in the motor and alternator which separates the moving Rotor and the Stator core.
Increase Air gap
- Magnetic flux link with rotor and stator decrease cause decrease in torque in motor and Generated voltage in alternator.
- Manetising current Increase.
- Magnetising reluctance decrease.
- Permeability decrease.
Decrease air gap
- Physical Damage of Stator core and the rotor.
- Not proper Cooling
- Dust Will accumulate in between gap.
- AIr gap decrease cause magnetic flux increase and change of getting overheat of winding and get damage.
Air gap :- 1.5 Cms to 2.0 Cms.
Clamp Meter and it’s working principle
It is an Electrical Measuring Device, which is used for measureing the Electric current of Current carrying conductor without having make physical Contact.
Working principle :- It works on the principle of Faraday’s law of electromagnetic Induction in order to make no-contact AC Current measurements.
Extinguisher used for Electrical fire.
- Dry Powder
Parameter check befor paralleling of generator
- Voltage and
It is a unit of electric charge, having Dimenstions equal to electric current multiplied by time equal to the charge flow through a steady current of one ampere in one hour.
Battery Capacity is the measure of amount of charge available in ampere-hours (AH ).
The battery capacity represents the maximum amount of energy that can be extracted from the battery under certain specified conditions.
How battery capacity is measured ?
The capacity of battery is measured by discharging at a constant current untill it reaches terminal voltage (usually it’s 1.75 volts ). It is usually done at constant temperature of 25 degree celcius.
The capacity is calculated by multiplying the discharge current value by the time required to reach terminal voltage.
It is a device used to transform high A.C to Low A.C.
Or, it is a device that is used fo transformation of current from a higher value of current into a proportionate lower current.
Current Transformer works in the principle of Faraday’s law of electromagnetic induction.
Materials used in Current Transformer is Silicon Steel Core.
It is used in Clamp meter.
Emergency Switch board Distribution
- Emergency Bilge pump (440 V)
- Sprinkler system (440 V)
- One of the steering gears (440 V)
- Navigation Equipment (220 V)
- Radio Communication (220 V)
- Transformed and rectified supply to Battery systems (220 V)
- Transitional Emergency Power Battery (Emergency lights for 30 minutes)
- Low power DC system Battery (Alarms and control system)
What are the equipment which get supply from emergency generator ?
- It is called emergency load
- Emergency lightening to alley way /boat deck / engine room.
- Navigation system
- Steering gear
- Emergency fire pump
- Emergency air compressor
- Battery charging
- Fire detecting and alarming system
- Radio equipments (Communication equipment)
- Daylight signaling lamp and ship’s whistle
- Navigation Aids
- General Alarm
- Manual fire alarm
- Watertight doors
It is an Automatic starting of an Essential Equipment when power is returned or backup after a total power failure.
Example :- Equipment start such as Fuel Oil pump, Steering gear motor, Lube Oil Pump, Sea water Pump etc.
Synchronous Motor and working principle
A synchronous motor is an AC Motor in which rotation of rotor or shaft is synchronised with frequency of Supply Current.
Or, an AC Motor which run with Synchronous Speed.
Note :- It is not self started motor. It is double excited motor run at constant speed.
Synchronous motor working principle :- It works on the principle of magnetic locking.
Why synchronous motor is not self started motor.
Synchronous motor works on the principle of magnetic locking. There is force act between Rotating Magnetic Field and Static magnetic field produced by DC supply in rotor. But, it does not able to rotate rotor due to inertia. So, it required external source to rotate.
In some synchronous motor, External source is DC Motor and by providing a special winding on the rotor poles, known as damper winding or squirrel cage winding
Difference between Motor and Generator
Motor 1. It is a device which converts electrical into mechanical energy. Generator 1. It is a machine which mechanical energy into electrical energy.
Motor 2. It consumes Electrical Energy. Generator 2. It generates electrical energy.
Motor 3. Mutual induction of magnetic field responsible for rotation of rotor. Generator 3. Rotor rotates bt external source.
Difference between DC generator and AC generator
1. DC generator used for generating Direct current. 2. Commutator is used. 3. It is used for generate less voltage. DC can not be generated at high voltages because sparking starts at the Commutator at high voltage and cause Commutator get damaged.
1. AC generator used for generating Alternating current. 2. Slip ring is used. 3. It is used for high AC voltage.
It is an electronic device that maintains constant voltage at output of generator under varrying load.
Or, It is a feedback control system that measures the output voltage of the generator, compares the output at the set point, and generates an error signal that is used to adjust excitation of the generator.
Components of AVR
- Zener diode
AVR working principle
It works on the principle of detection of error.
Note :- Error signal is used to adjust field current by increasing or decreasing the current flow to am exciter stator.
Synchroscope working and working principle
It works on the Principle of magnetic locking between static field (Pole ) and rotating magnetic field ( in the armature winding).
Main parts :- 1. Motor poles and 2. Armature Winding
It consists of small motor with coils on two poles connected across two phase of the the incoming generator name R and Y.
Notes :- Static magnetic field N and S poles Generated due to two phase. If three phase then generates rotating magnetic field.
There is Armature Winding, supplied from Red and Yellow phase from switchboard bus bar.
Armature Winding consists of two parallel coil in armature Winding. With one coil resistance and with another coil Inductor is connected.
Inductor is connected parallel with resistance which delaying the current by 90° to current of resistance. It create phase difference and create rotating magnetic field in armature Winding.
Polarity of Rotating Magnetic Field change alternatively in North and South. Rotating magnetic field will react with the poles of motor and turn the rotor clockwise and anticlockwise.
If it is rotating in clockwise that means incoming generator has more frequency that running generator. If it is rotating in anticlockwise, means frequency of incoming generator is less than running generator.
Note :- Frequency of incoming generator increase or decrease by means of speed adjuster of prime mover mover.
Three Lamp method
What is a Diode
A diode is a semiconductor that allows the flow of electricity in one direction only and block the flow in the opposite directions.
Note :- It is regarded as one-way valves and they are used in various circuits, usually as a form of protection.
Example :- Light emitting diode ( LED ), Rectifier Diode and photodiode.
- Rectifying a voltage: turning AC into DC voltages.
- isolating signals from a supply
- Controlling the size of a signal
- Mixing (multiplexing) signals.
Use of diode in alternator
Diode is used in Alternator as a diode rectifier which convert A.C into DC in AVR.
A zener diode is a diode which permits current not only in the forward directions like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as zener knee voltage or zener voltage.
Example :- In AVR, Intrinsically safe Equipment
- As a Voltage stabilizer for low-current applications
- Generations of reference voltage ( Ex – for an amplifier stage )
- Switching applications
- Clipper circuit and
- surge suppressor
Silicon Controlled Rectifier or Thyristors
Silicon :- Semiconductor Materials. Rectifier:- Convert AC to DC. It control AC to DC
A SCR is a unidirectional semiconductor device made up of Silicon which is used to change alternating current into direct current and at the same time can control amount of power fed to the load.
Note :- Thus, SCR Combines the features of a rectifier and a transistor.
Application of SCR
- AC power control (including lights, motors etc. )
- AC power switching ( as a switch )
- Pulse control
- Over voltage protection
- Phase control :- Control elements in phase angle triggered cintrollers
- Speed control
Use of SCR in alternator
Silicon Controlled Rectifier is used in AVR for Controlling the amount of excitation current to maintain constant voltage at output of generator.
Use of Rectifier
In motor , alternator and AVR
It is a type of semiconductor whose resistance vary with change in Temperature (🌡️).
- Fire alarms
- Measure Motor winding temperature
- Thermal relay
- Digital Thermometer
Types of Circuit breaker
On the basis of arc quenching medium
- Air circuit breaker
- Vaccum circuit breaker
- Oil circuit breaker
- SF6 circuit breaker
What is CKT breaker
A circuit breaker is a electrical switch designed to protect an electrical circuit from damage caused by excess current typically resulting from overload or short circuit.
It is an electrical switch which is used for close or open the circuit bin normal or faulty conditions.
Faulty conditions :- Overload,over current and short circuit.
Functions :- It’s function is to intrupt current flow after a fault is detected.
Note :- It can be operated manually or automatically.
Difference between fuse and Circuit breaker
Types of motor used in Engine Room
1. Single phase :- Small pump, Drilling machine, Exhaust fan in bathroom of cabin.
2. Three phase :- Engine auxiliary pump, Blower fan, Main Fire Pump, S.W pump
1. Single phase :- Radar Gyrocompass
2. 3 phase :- Bow thruster, Propulsion of ship
Lifeboat davit safety
Locations of libeboat davit and purpose
Lifeboat davit limit switch is a safety device which limit the motion of davit when reaches the inboard position and make impossible for operator to make a mistake.
Or, it is a safety device which limit the davit arms when reaches final stowed position.
Locations :- It is fitted on the base of davit arm.
It is the ratio of True poper to Apparent power. Or, It is the cosine of angle between current and voltage.
Cos $ = Real power / Apparent power
Significance of Power factor
It is measure of how much contribution of real power in apparent power.
Cos$ = 0.8 , it means 80 percent of apparent power ( KVI ) is used as real power ( KW ) ( mechanical or heat and light ).
Low power factor implies low power consumption.
How can you improve power factor
- Using Capacitor bank in parallel
- Phase Advancer
- Synchronous Condenser
Why capacitor is Used in parallel. It is because in parallel equipment capacitance increase and this increase in the charge storage. Q = C eq × V
Reason for low power factor
1. The main reason for low power factor is Inductive load. Mainly Induction Motor. 90 percent of load consist of induction machine. Such machine draw magnetising current to produce magnetic field hence work at low power factor.
2. Variations in power loading b:- When system is loaded lightly ,the voltage increase and the current drawn by machine also increase. Thus, results in low power factor.
3. Harmonic current
Disadvantages of low power factor
- arge KVA ratings and size of electrical equipments.
- Poor voltage regulations
- Large Copper Loss
- Greater conductor size
Why DC supply is given for Excitation
When we supply DC as a exciter then it generates static magnetic field in the form of North and South pole. If we supply AC then it generates rotating magnetic field and it does not create locking with with rotating magnetic field of Stator winding.
Thus, it fails to synchronise with rotating magnetic field of Stator winding and rotor will not move.
How to control speed of induction motor
1. By changing the supply voltage of the motor I e star to delta but in this condition only two speed slow or fast . Note :- If asked to change speed ( not control ) of induction motor then add this point.
2. By changing stator pole number of the motor. It is not possible to change no. Of like each time so, we use
A. ) PAM ( Pulse Amplitude Modulation)
B .) Multiple stator winding method
3. By changing the frequency of power Supply ( by using frequency converter MOSFET’S )
4. Adding rheostat in the stator circuit.
The speed controls of three phase induction motor from rotor side are further classified as:
1. Adding external resistance on rotor side.
2. Cascade control method.
3. Injecting slip frequency emf into rotor side.
Speed control of Synchronous motor
This speed can be changed by changing the number of poles or frequency of supply.
1. No of poles
2. By changing the frequency of Supply side. It is done by using rectifier and inverter in open or closed loop mode.
How to control speed of DC motor
the voltage equation of a simple DC motor is
V = Eb + IaRa
V is the supplied voltage, Eb is the back EMF, Ia is the armature current, and Ra is the armature resistance.
We already know that
Eb = (PøNZ)/60A.
P – number of poles,
A – constant
Z – number of conductors
N- the speed of the motor
Substituting the value of Eb in the voltage equation, we get
V = ((PøNZ)/60A) + IaRa
Or, V – IaRa = (PøNZ)/60A
i.e., N = (PZ/60A) (V – IaRa)/ ø
The above equation can also be written as:
This implies three things:
2. The speed of the motor is directly proportional to supply voltage.
2. The speed of the motor is inversely proportional to the armature voltage drop.
3. Speed of the motor is inversely proportional to the flux due to the field findings
Thus, the speed of a DC motor can be controlled in three ways:
1. By varying the supply voltage
2. By varying the flux, and 3. by varying the current through the field winding
4. By varying the armature voltage, and by varying the armature resistance
Types of load
Three basic types of loads exist in circuits: capacitive loads, inductive loads and resistive loads.
1. Resistive load
Load which consumes only active power is called as resistive load. Or, The resistive load is a load which obstructs the flow of electrical energy in the circuit and converts it into thermal energy, due to which the energy dropout occurs in the circuit.
Example :- lamp and the heater
Note :- The resistive loads take power in such a way so that the current and the voltage wave remain in the same phase. Thus the power factor of the resistive load remains in unity.
2. Capacitive load
Capacitive loads include energy stored in materials and devices, such as capacitors, and cause changes in voltage to lag behind changes in current.
Example :- Capacitor, Capacitor bank, buried cable , capacitor in fan, Generator AVR, 3 phase induction motor
Notes :- 1. Voltage lags 90° from voltage. 2. Current leads 90° forward the voltage.
3. Inductive load
It is a load which convert electrical energy into magnetic field.
Example :- motors, transformers and chokes, Vaccum cleaner, washing machine etc.
Notes :- The current wave of the inductive load is lagging behind the voltage wave, and the power factor of the inductive load is also lagging.
1. Voltage leads 90° by current. 2. Current lags 90° behind the voltage.
Generator producing no Voltage
- Loss of Residual Magnetism
- Failure re of AVR
- Failure of Excitation components.
Generator producing less voltage and Rectification
1. Load applied to Generator exceeds the capacity , will cause machine slow down and drop in frequency and voltage.
Remedy :- Run another generator in parallel.
2. AVR Voltage gain set too low to respond to load being applied.
Remedy :- Increase voltage gain set.
3. If AVR feedback is from generator bus bar voltage terminal and voltage dip too far, all excitation could be lost and typically result in under voltage.
Remedy :- AVR feedback to be close the generator.
4. Speed control gain (Speed droop ) set too low.
Remedy :- Increase speed droop set.
5. Fuel injector problem, governor problem, Air filter clogged, faulty air coolers etc.
Remedy :- They must be rectified.
Use of Capacitor
- Use to reduce voltage pulsation
- Used for storage of energy ( Power bank )
- Motor starter [ Use of capacitor in motor (single phase motor ) to create a poly phase ( varying magnetic field ) from a single phase power supply
- Capacitor used in fan
- Power factor correction
Use of diode, zener diode in alternator
Use of Diode :- Diode us used a bridge rectifier ( AC to DC ) in alternator.
Use of zener diode :- Zener diode is used as a generation of reference voltage. So, to produce error supply for Excitation and as voltage stabilizer in AVR.
It is a sensor that is used to detect the movement or presence of an objects without making physical contact with the object and convert into an electrical signal.
Advantages :- It is no contact sensor, and cause no damage to object.
Working principle:- It works on the principle of Faraday’s law of electromagnetic induction.
Applications :- It is used for sensing the RPM of main engine.
Inductive proximity switch Working :-
It has electromagnet coil in which supply given is from 24 V DC Source and another coil when magnetic flux changes due to metal sensing on flywheel, current is induced in secondary coil.
Magnetic pick up sensor is same as proximity switch but rhe only difference is , in place of electromagnetic coil there is a permanent magnet
Main switchboard safeties
- Fuse,relay, circuit breaker
- Under voltage relay
- Reverse power trip
- Preferential trip
- Over current trip
- Short circuit trip
- Earth fault indicator
- Arc Chute
- Ebonite rod ( to remove static charge )
- Dead front type Switch board :- It is a safety wherein you can not open the panel untill the power of that panel is switched off.
- Insulated hand gloves
- Dry boiler suit
- Shoes without metallic part
- Rubber pad in front of the switchboard
- 0.6 m gap behind switchboard
- Panel doors to be earthed
- Intelocked handles for opening door
- No water, oil, or steam pipeline in its vicinity.