June 2019 Electrical Oral

Question Bank

Antriksh Singh Negi

DMET 2018
Electrical Oral

Q1.) What is SCR and what are thyristors

A thyristor is a four-layer semiconductor device, consisting of alternating P type and N type materials
(PNPN). A thyristor usually has three electrodes: an anode, a cathode, and a gate (control electrode).

The most common type of thyristor is the silicon-controlled rectifier (SCR). When the cathode is
negatively charged relative to the anode, no current flows until a pulse is applied to the gate. Then the
SCR begins to conduct, and continues to conduct until the voltage between the cathode and anode is
reversed or reduced below a certain threshold value. Using this type of thyristor, large amounts of power
can be switched or controlled using a small triggering current or voltage.

Thyristors are used in motor speed controls, light dimmers, pressure-control systems, and liquid-level
regulators.

Q2.) Brushless alternator

A brushless alternator is composed of two alternators built end-to-end on one shaft. Smaller
brushless alternators may look like one unit but the two parts are readily identifiable on the large
versions. The larger of the two sections is the main alternator and the smaller one is the exciter.
The exciter has stationary field coils and a rotating armature (power coils). The main alternator
uses the opposite configuration with a rotating field and stationary armature. A bridge rectifier,
called the rotating rectifier assembly, is mounted on the rotor. Neither brushes nor slip rings are
used, which reduces the number of wearing parts. The main alternator has a rotating field as
described above and a stationary armature (power generation windings).

Varying the amount of current through the stationary exciter field coils varies the 3-phase output
from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor,
and the resultant DC supplies the rotating field of the main alternator and hence alternator output.
The result of all this is that a small DC exciter current indirectly controls the output of the main
alternator.

Q3.) What to do if synchroscope doesn't work

In case synchroscope does not work we use either bright lamp method or Dark lamp method whichever is
available.
Bright Lamp Method
In this method, one lamp is connected between corresponding phases while the two others are cross-connected
between the other two phases as shown in the figure below.

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Dark lamp method

A set of three synchronizing lamps can be used to check the conditions for paralleling or synchronization of the
incoming machine with the other machine. A dark lamp method along with a voltmeter used for synchronizing is
shown below. This method is used for low power machine.

Advantages of the Dark Lamp Method

 This method is cheaper.

 The correct phase sequence is easily determined.

Disadvantages of the Dark Lamp Method

 The lamp becomes dark at about half of its rated voltage. Hence, it is possible that the synchronizing switch
might be switched off even when there is a phase difference between the machine.

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 The filament of the lamp might burn out.

 The flicker of the lamps does not indicate that which lamp has the higher frequency.

Q4.) What to do if synchronizing lamps also doesn't work

If synchronizing lamp doesn’t work, we use voltmeter method

Q5.) Earth lamp, how many

 It is a set of lamps, which show the presence of earth fault in distribution system.

 If earth fault occurs the lamp will show dim light or goes out because potential is zero.

 If phase ‘R’ is earth fault, lamp ‘R’ becomes dark while the other two lamps burn with
extra brightness

 Each lamp is connected to secondary connections of each single phase step-down transformer,
and primary connections are common to star point, which is earthed to ship structure. (one phase
and common neutral point)

 Normally 3 earth lamps burn with equal brightness if there is not fault

 The location of fault can be traced by switching off the individual branch circuit breaker
and check the condition of earth lamp.

 When branch circuit with fault is switched off, dark lamp will become normal glow and all
3 lamps burn with equal brightness.

When “EARTH LAMP” switch (ELS) on a feeder panel is in OFF position, the neutral of the star
connected primaries of three lamp transformers is disconnected from the earth, and the voltage across the
primary is the same for each transformer regardless whether the ship’s feeder system contains an earth
fault or not. Therefore, three indicator lamps (TLs) connected to the respective transformer secondary are
on at the same brightness.

To check the ship’s feeder system’s insulation resistance to earth, put “EARTH LAMP” switch (ELS) to
TEST (this earths the neutral of the star connected primaries of lamp transformers). If there is an earth
fault in phase R, for example, the lamp R would be less bright than other two; or if it is a complete earth
fault, the lamp R would be off. Where there is no earth fault, switching of the ELS from OFF to TEST
gives no change in lamps’ brightness.

Q6.) Bus bar function

An electrical bus bar is defined as a conductor or a group of conductor used for collecting electric power
from the incoming feeders and distributes them to the outgoing feeders. In other words, it is a type of
electrical junction in which all the incoming and outgoing electrical current meets. Thus, the electrical bus
bar collects the electric power at one location.

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Q1.) Types of earth fault. How to find earth fault

a) 110V earth Fault
b) 220V earth fault
c) 440V earth fault
To find

Q2) What are the steering gear motor safeties?

a) Overload alarm.
b) 200% insulation in motor.
c) High temperature alarm.
d) Self-starting after power failure.
e) Short circuit trip.
f) Phase failure alarm.
g) One of the steering motor is fed from the emergency bus.

Hydraulic side there is two trips

a) Low level cutout
b) High lube oil temperature cutout

Q3) What are Intrinsically safe equipment?

Intrinsically safe equipment is defined as "equipment and wiring which is incapable of releasing sufficient
electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous
atmospheric mixture in its most easily ignited concentration."
Where used and name one intrinsically safe equipment

Q4) What is a relay

So relay is a switch which controls (open and close) circuits electromechanically. The main operation of
this device is to make or break contact with the help of a signal without any human involvement in order
to switch it ON or OFF. It is mainly used to control a high powered circuit using a low power signal.
Generally a DC signal is used to control circuit which is driven by high voltage like controlling AC home
appliances with DC signals from microcontrollers.
Types of relay
1.ELECTOMAGNETIC
2.SOLID STATE
3.THERMAL

Q5) Why can't we start DC generators with no load

Surely you can run a dc series generator under no load if you attach it to a prime mover. But In DC series
generators field winding is connected in series with armature and load. Hence, the field current is same as
the load current. Now under no load condition the load terminals are open circuited thus there will be no
current in the field winding and hence no excitation would be available. Thus no emf would be induced.

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Int:k. Basu

1. Purpose of fan in motor

To provide cooling effect in motor.
2. Why adequate air gap in stator n rotors
It will increase the coupling between the rotor and stator, which is essential for the function of an
Induction Motor.
 inductance of the stator windings will increase
 the flux in the air gap will increase
 therefore, torque production will increase
 the iron losses will increase (hysteresis), and perhaps saturate, limiting the flux increase
 The air gap anomolies (stator teeth and rotor teeth) will be exacerbated, torque ripple will
increase and 2E vibration will increase
 the eddy-current losses will increase

If the air gap of an induction motor is increased, the following will happen:
 The permeability of the magnetic circuit rotor-to-stator will decrease.
 The magnetizing inductance of the motor thus decreases.
 The magnetizing current will increase. This will cause a poorer power factor at all loads.
 The magnetic flux in the air gap will decrease and leakage fluxes will increase. This will
cause a reduction in the maximum available torque

3. Safety in circuit breaker

4. Factor on which motor rpm depends

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1)diode,use and any one place where it is in generator

Main functions. The most common function of a diode is to allow an electric current to pass in one
direction (called the diode's forward direction), while blocking it in the opposite direction (the reverse
direction)

2) paralleling of generator

3)transformer, use, losses (cross question)

4)speed control of motors

5) earth fault and cross questions

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1.Air gap

2.Person has got chemical burn, what to do?

a) Rinse and Clear Burn Area

b) Flood area with cool water for at least 20 minutes or until help arrives.

c) Make sure water doesn't flow onto another part of the person's body or onto you.

d) Don't use a strong stream of water, if possible

e) As you flush the burn (not before), remove jewelry or articles of clothing with chemical on them,
unless they're stuck to the person's body.

f) After flushing the burn, follow instructions on the label of the chemical product, if available.

g) Don't try to neutralize the burn with acid or alkali. This could cause a chemical reaction that worsens
the burn.

h) Don't put antibiotic ointment on the burn.

3.Electrical shock, what will u do?

a) When approaching a person in contact with electricity, it has to be ensured that the victim is not
under current contact any more. The power of electrical power should be switched off If possible.
b) If the current cannot be switched off, put on rubber gloves and rubber boots, or stand on an
insulating rubber mat before approaching and touching the casualty. If the victim is entangled in
electrical lines, try to remove the lines with a wooden pole, a wooden chair, an insulated cord, or
any other suitable non-metal object.
c) Check immediately for breathing and heartbeat.
d) If the casualty is not breathing, give artificial respiration.
e) If there is no heartbeat, apply chest compressions.
f) When breathing is restored, cool any burned areas with cold water and cover with a clean, dry,
non-fluffy dressing.
g) Treat as for heat burns (i.e. relieve pain, prevent or treat shock, and prevent or treat infection)

4.Why deck motors have no cooling fan?

5.Filler gauge material for air gap?

Feeler gauges are commonly made out of tempered tool steel or stainless steel.
But feeler gauge used to measure alternator air gap are made up of plastic or other non-conducting
material to provide safety from electrical shock.

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A Zener diode is a type of diode that allows current to flow not only from its anode to its cathode, but
also in the reverse direction, when the Zener voltage is reached. Zener diodes have a highly doped p–n
junction.
fun. 5

Electrical
1. Regulations of emergency generator.
2. Motor overheat, what to do?
3. Shore supply, cross questions, factors to be taken care of?
Following things to be checked before connecting shore supply to ship in a drydock:

 Check the cable drawn to ship for providing shore supply is in excellent condition

 Check the insulation resistance of the cable provided for the shore supply

 Check the insulation resistance of the shore supply box

 Check the polarity of shore supply using a voltmeter

 Check and ensure the frequency and voltage of shore supply are matching with the specifications
required by the ship

 Check the phase sequence of the shore supply using phase sequence tester

 Check the tightness of the shore cable connector clamp to ensure they are not loose

 Ensure to display notice near the vicinity of ship’s receiving terminal box about high power
cable in use

 Check and ensure the ship’s generators are disconnected from the Main Switch Board of the ship

 A responsible officer must check and record the energy meter reading provided on shoreside

 Ensure ship’s hull is earthed to the shore before supplying shore power to the ship

4. Relay, cross questions

5. Battery room safeties, i told 5-6 points, still wanted to hear more.
Electrical

Msb safety

 Overload trip

 Preferential trip

 Under voltage trip

 Over voltage trip

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 Reverse power relay (No voltage trip)

 Reverse current trip

 Fuse

 A .C .B( Air circuit breaker )

 Earth lamps.

 Low frequency trip

 Meters

 Synchroscope

 Emergency synchronizing lamp

 Ebonite handrail and Rubber footstep

Motor safety
Thermistor & thyristor difference
A transistor is a device that allows you to control its resistance from an input voltage or current.
A thermistor is a device whose resistance changes with temperature
A thyristor is a device that switched rapidly from a very high resistance to a very low one according to n
input current/voltage.. You have to take the power off to reset it to a high resistance.

Thermistor are of two opposite fundamental types:

 With NTC thermistors, resistance decreases as temperature rises. An NTC is commonly used as a
temperature sensor, or in series with a circuit as an inrush current limiter.

 With PTC thermistors, resistance increases as temperature rises. PTC thermistors are commonly
installed in series with a circuit, and used to protect against overcurrent conditions, as resettable
fuses.

Earth fault and cross questn

Residual magnetism(X)
what if DG not generating voltage.
Residual magnetism is defined as the amount of magnetization left behind after removing the external
magnetic field from the circuit. In another word the value of the flux density (ob as shown in the figure
with the red color line) retained by the magnetic material is called Residual Magnetism and the power of
retaining this magnetism is called Retentivity of the material.

Reverse power trip-(X)how does it work

Intrinsically safe meaning(X) where we use

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Interlock- (x)where,
Ext - Kank Basu
Int - Chakki
1. What is relay ? How relay works . Different type of relay its uses ?
2. How will u take shore connection ? Can u start EMG. Generator when u had shore supply on board ?
How will check the phase ? If not in phase what will u do ?
3.Types of fuses ? How will u come to know that fuse is blown ?
4.Safties on MSB ?
5 ? How will u find ?
Electrical..
Engine crane safety? and how many limit switches are there?
When two generator are running in parallel ..what is the cause if excitation of one generator fails?
What is the cause of motor failure in engine room?

1. Electrical Overload

Electrical overload or over-current is caused by an excessive current flow within the motor windings,
exceeding the design current which the motor is able to carry efficiently and safely. This can be caused by
a low supply voltage, resulting in the motor drawing in more current in an attempt to maintain its torque.
It can also be a result of short circuited conductors, or an excessive voltage supply.
Possible solution: Electrical overload can be prevented by installing effective over-current protection
which will detect overcurrent and interrupt supply.

2. Low Resistance

The most common cause of motor failure, and arguably the most difficult to overcome, is low resistance.
Low resistance is caused by the degradation of the insulation of the windings due to conditions such as
overheating, corrosion, or physical damage. This leads to insufficient isolation between the conductors or
motor windings, which can cause leakages and short circuits, and eventually motor failure.
Possible solution: The insulation should be regularly inspected for signs of wear, and replaced before low
resistance is able to cause failure.

3. Over-Heating

Around 55% of insulating failures in motors occur due to overheating. Overheating can be caused by poor
power quality, or a high temperature operating environment. For every 10oc that the temperature of a
motor rises, the insulation life reduced by 50%.
Possible solution: It is critical that the motor is kept as cool as possible, ensuring the operating
environment is kept cool if possible will help prevent breakdowns.

4. Contamination

Contamination from dust, dirt and chemicals is one of the leading causes of motor failure. Foreign bodies
which find their way inside the motor can dent bearing raceways and balls, leading to high levels of
vibration and wear. It can also block the cooling fan, limiting the motor’s ability to regulate its
temperature, and increasing the likelihood of overheating.
Possible solution: Preventing contamination is relatively easy. Keep work areas, tools and fixtures as
clean as possible to help eliminate the chance of contamination entering the motor. Also, when laying out

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the workspace, try to position motors away from grinding machines which produce large amounts of
contaminants.

5. Vibration

Vibration can lead to many issues with the motor, and can eventually cause the motor to fail prematurely.
Vibration is often caused by the motor being positioned on an uneven or unstable surface. However,
vibration can also be a result of an underlying issue with the motor, such as loose bearings, misalignment,
or corrosion.
Possible Solution: Motors should be checked regularly for vibration, using a motor analysing tool such
as the SKF EXP4000 Dynamic

Why we take insulation resistance when the motor is hot?

Result : safety
Electrical
MSB safety(cross questions )
Parallel generator
Merger(voltage, construction, working)
Shore terminal box(location fittings)
Lots of cross question....
Electrical
Transformer everything about transformer rating types , losses
Difference between ACB and relay.❌❌
Energy Meter
Definition: The meter which is used for measuring the energy utilises by the electric load is known as
the energy meter. The energy is the total power consumed and utilised by the load at a particular
interval of time. It is used in domestic and industrial AC circuit for measuring the power consumption.
The meter is less expensive and accurate.

A no-volt coil, under-volt coil, no-volt release or under-voltrelease is part of the control gear of a circuit
breaker or large isolator. It is a solenoid, or logic function, that monitors the incoming supply and if the
supply is de-energised it trips or opens the main contacts
Skin effect is the tendency of an alternating electric current (AC) to become distributed within
a conductor such that the current density is largest near the surface of the conductor, and decreases with
greater depths in the conductor.
How to control induction motor speed.❌❌
Clamp meters rely on the principle of magnetic induction to make non-contact AC current measurements.
Electric current flowing through a wire produces a magnetic field. Since alternating current frequently
reverses polarity, it causes dynamic fluctuations in the magnetic field which are proportional to the
current flow. A current transformer inside the clamp meter senses the magnetic fluctuations and converts
the value to an AC current reading. This type of measurement is convenient for measuring very high AC
currents.
Direct current, however, flows through conductors in a fixed polarity. Consequently, the magnetic field
around the conductor does not change and conventional clamp meters will register no reading. DC clamp
meters work on the principle of the Hall Effect. Hall effect sensors sense the magnetic field caused by

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current flow which causes a small voltage across the Hall effect sensor. That voltage, which is
proportional to current is then amplified and measured.
Clamp meters often include other sensors such as voltmeters, ohmmeters, etc. which increase the
versatility of the instrument. These other sensors use test leads which plug into the clamp meter. As only
current measurements can be made with the clamp, other measurements d

Earth fault❌❌
The RMS value is the effective value of a varying voltage or current. It is the equivalent steady DC
(constant) value which gives the same effect. For example, a lamp connected to a 6V RMS AC supply
will shine with the same brightness when connected to a steady 6V DC supply.
Moter drowned in water what to do.❌❌
1. Zener diode characteristics with drawing.

2.Shore connection and cross questions.

3.at how much voltage u will charge a battery? Drawing?
And what are maintenance free batteries....
4.Brushless alternator with drawing.
5.reverse power trip use? Cross mai ACB and safeties involved.
6. Undervoltage protection.

Result: Function 5 pass, Function 3 repeat

Electrical:-

1. Earth fault , types , how to find.

2. Alternator inside and outside maintenance.
3. Steering motor electrical safeties
4. Power factor and factors which reduces the power factor.
5. Effect of air gap when ... reduces & increases and instrument to measure air gap & material.

1. E/r crane safety, working of electomagnetic brake, and XX

2. Diode, its fn, rectifier, avr, XX
4.Exact location of diode in alternator
3. Induction motor speed contol, XX
DC motor speed control
5. Shore connection, Many XX

1 mcb safety. Circuit breaker. Fuse & it's type❌❌

2types of starter. ❌❌
3why we cannot use DC in transformer.
4relay& on what factor it depends. ❌❌
5what do u mean by reverse power & reverse power trip working❌❌

Function 5. Ext basu int dont know

1.electrical safety for lifeboat davit
2.diode,what is its use,where it is use in alternator, and why dc current in alternator
3.proximity switch, distance between flywheel and rpm pickup sensor

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4.earth fault,types,how to know this fault,and how to identify where is the fault occurs
5 transformer working,losses,which is constant and whch is variable

Result function 5
F-5
*Intrinsically Safe Circuit
*Gap between magnetic pickup sensor and flywheel
*Earth fault how to find
*Turning gear motor safety
*Not recall

Electrical:
Earth fault troubleshooting
Alternator maintenance generator maintenance
Air gap check ,bearing check
Msb safeties synchroscope parallel m kaise.lete h generator..all.methods
Phase sequence indicator
Result: electrical
[22:24, 9/5/2019] +91 98308 36034: Electrical

1.How to check IR of DC motors? How is it different from AC motors?

2.Exciter vs Equalizer?
3.Megger vs Multimeter?
4.A fuse has blown in a line and you have no specifications written on it how will you replace it if you
have many fuses of various ratings?
( I said 2 ya 3 answer like measure kr lenge parameters baki lines ki aur uske hisab se, current dekh lenge
line ki, FLC dekh lenge device ka, baki fuses ko dekh lenge he wasn't satisfied enough)
5.Your gen has an electrical fault and it can't be started without correcting it what is the fault? (Loss of
residual magnetism bole to bola that is not a fault! Give me a fault)

1. Two generator running in parallel if one loses excitation what will happen
2. How to measure DC motor IR
3. Devit electrical maintenance
4.Motor maintenance
5. AVR maintenance

- if one generator looses excitation what will happen

- ir testing of dc motor
- there are 3 winding, how will you know that they are r y b respectively
- in a motor junction box there is start and stop button and there is no labelling, how will you know which
one is start button
-IR loss reasons?
What is tracking

Electrical
Ex(d)
Msb safety

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Induction motor ir test

Excitation
Alternator maintenance

1- dark lamp method for synchronising of alternators.

2.induction motor working principle. Cross questions regarding stator rotor . Safeties of motor.
3. Air gap between stator and rotor
Cross questions about the effects of increasing/ decreasing the gap.
Effect on p.f the motor
4. Fuses. Types of fuses. Wanted detailed information.
5. What is semiconductor. Example
A semiconductor is called a semiconductor because it is a type of material that has an electrical resistance
which is between the resistance typical of metals and the resistance typical of insulators, so it kind of, or
"semi"-conducts electricity. Semiconductors are used in many electrical circuits because we can control
the flow of electrons in this material, for example, with a controlling current.
6. Zener diode working.
7. Thermistor working
8. Thyristor , transistor working
9.generator maintenance
Understanding The Power Factor

By Kiran Daware Power System

Energy is needed and utilized everywhere in the world. From the point of view of convenience, efficiency
and economy, it is best that we generate, transmit and distribute it in electrical form before it is converted
into the required one by suitable equipments. For the same reasons of economy and efficiency, we use AC
rather than DC. Practically, we generate, transmit and distribute energy in AC form almost exclusively.
DC is used either in DC applications (DC machines and electronic circuits) or in HVDC transmission
links.

Wherever AC power is utilized, the question of power factor arises itself.

Power Factor
 Defined as 'the cosine of the angle between the voltage and current'.
 In AC circuit, the voltage and current are ideally in phase.
 But practically, there exists a phase difference between them.
 The cosine of this phase difference is termed as power factor.

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 It can be defined and mathematically represented as follows:

From the fig. (a) above, it can be clearly noted that there is a phase difference of angle ɸ between the
voltage phasor and the current phasor.
Power Factor = cosɸ

The fig. (b) is called as Power Triangle

Here, VI sinɸ = Reactive power (in VAR)
VI cosɸ = Active power (in Watts)
VI = Apparent power (in VA)
PF = cosɸ = Active Power (W) / Apparent Power (VA)

The fig. (c) is called as Impedance Triangle

Here, R = Resistance, X = Reactance, Z = Impedance
2 2
Z = R + X2
PF = cosɸ = R/Z

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The Power Factor can be lagging, leading or unity.

Lagging Power Factor

 When current lags behind the voltage, the power factor of the circuit is called 'Lagging'
 When the circuit is inductive, the pf is lagging.
 The loads such as induction motors, coils, lamps, etc are inductive and have Lagging pf.

Leading Power Factor

 When current leads the voltage (or voltage lags behind the current), the power factor of the circuit
is called 'Leading'.

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 When the circuit is capacitive, the pf is leading.

 Capacitive loads such as Synchronous condensers, capacitor banks etc draw leading current. Such
circuits have leading power factor.

Unity Power Factor

 Power factor is unity (i.e. 1) for ideal circuits.

 When current and voltage are in phase, PF = 1
 Power factor cannot be more than unity.
 Practically, it should be as close to unity as possible.
If power factor is low, following problems are encountered:

Effects Of Low Power Factor

1. Load Current
Power in an AC circuit can be given as: P = VI cosɸ
Therefore, cosɸ = P / VI
I ∝ 1 / cosɸ
Similar relationship can be derived for 3 phase circuit too. We can see that current is inversely
proportional to pf.

For example, consider that we want to transfer 10 kVA power at 100 V

If PF = 1,
I = P / (V cosɸ) = 10000 / (100 x 1) = 100 A

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If PF = 0.8,
I = P / (V cosɸ) = 10000 / (100 x 0.8) = 125 A
Hence, the current drawn is higher for low power factor.
2. Losses: As stated above, for low pf, the current drawn is high. Hence copper losses (I 2R losses)
will also be high. This decreases the efficiency of the equipment.
3. Overheating of the equipment: I2R losses produce heat (Joule's law). Hence, the temperature
rise will be relatively more for low PF which will further increase the stress on the insulation.
4. Size of conductor: Low power factor causes higher load current. If the load current increases, the
size of the conductor required will also increase. This will further increase the conductor cost.
5. kVA rating of the machine: Machines are not rated in kW while manufacturing because the
power factor of supply is unknown. Instead, they are rated in kVA.
According to definition, Cosɸ = Active power (kW) / Apparent power (kVA)
Hence, kVA rating = 1 / cosɸ
Therefore, for low pf, equipment of larger kVA rating is needed. But larger kVA rating means larger
size of the equipments. If size increases, the cost also increases.
6. Voltage Regulation: It is defined as the difference between sending and receiving end voltage
per unit sending end voltage. When power is transferred from one end to another, the voltage drops
due to several reasons. This voltage drop should be within permissible limits.
P = VI cosɸ , Therefore I ∝ 1 / V
For low power factor, current will be more and hence voltage drop will be increased. Hence, the
voltage regulation at low power factor is poor.
7. Active and Reactive power (Power Transfer Capacity): Active and reactive power both are
transferred over the line together. Active power is needed for supplying the load. Reactive power is
needed to maintain the voltage of the line. But if reactive power is more, then active power
transferred is decreased. For low pf, active power is low because, cosɸ = Active power (W) /
Apparent power (VA). This results in uneconomic operation.

Result:- Repeat�
ANSWER:
Overcurrent protection is protection against excessive currents or current beyond the acceptable current
rating of equipment. It generally operates instantly. Short circuit is a type of overcurrent. Magnetic circuit
breakers, fuses and overcurrent relays are commonly used to provide overcurrent protection.

Overload protection is a protection against a running overcurrent that would cause overheating of the
protected equipment. Hence, an overload is also type of overcurrent. Overload protection typically
operates on an inverse time curve where the tripping time becomes less as the current increases. Overload
relays as well as “slow blow” fuses are commonly used to provide overload protection.

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Some devices provide both overcurrent and overload protection. A thermal-magnetic circuit breaker has
both thermal (overload) and magnetic (overcurrent) elements. Both elements operate as described above.
Likewise the dual element fuse has both instantaneous and inverse time characteristics in the same fuse
providing both overcurrent and overload protection.
electrical(5),
Overload Relay Applications

The applications of an overload relay include the following.

 An Overload relay is extensively used to protect the motor.
 An overload relay can be utilized for detecting both overload conditions as well as fault
conditions & then declare trip commands for a protective device.
 Overload relay has developed into microprocessor systems as well as solid-state electronics.
 Overload relays deactivate the device whenever it pulls extreme current.

Advantages of ac over dc:

1. We all know that we got ac supply in our homes and we got this supply by transmitting ac over
long distances. AC can be transmitted using step up transformers but direct current or dc can not be
transmitted by this method.

2. The ac is easy to generate than dc.

3. It is cheaper to generate ac than dc.

4. The ac generators have higher efficiency than dc.

5. The loss of energy during transmission is negligible for ac.

6. The ac can be easily converted into dc.

7. The variation of ac can easily be done using transformers either step up or step down.

8. The value or magnitude of ac can be decreased easily without loss of excess of energy. This can
be done by using choke coil.
KVA: APPARENT POWER
kVA is a measure of apparent power: it tells you the total amount of power in use in a system. In a 100%
efficient system kW = kVA. However electrical systems are never 100% efficient and therefore not all of
the systems apparent power is being used for useful work output.
KW: ACTUAL POWER
kW is the amount of power that is converted into a useful output. kW is therefore known as actual
power or working power.

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Electrical Oral

Navigation Light System

Feeder
Navigation lights (mast head, side and stern lights) are to be fed by their own exclusive distribution board
located on the navigation bridge. The distribution board is to be supplied from the main as well as from
the emergency source of power. A means to transfer the power source is to be fitted on the navigation
bridge.
Branch Circuit
Each navigation light is to have its own branch circuit, and each branch circuit is to be fitted with a
protective device.
Duplicate Lamp
Each navigation light is to be fitted with duplicate lamps.
Control and Indication Panel
A control and indication panel for the navigation lights is to be provided on the navigation bridge. The
panel is to be fitted with the following functions:
A means to disconnect each navigation light.
An indicator for each navigation light.
Automatic visual and audible warning in the event of failure of a navigation light. If a visual signal device
is connected in series with the navigation light, the failure of this device is not to cause the extinction of
the navigation light. The audible device is to be connected to a separate power supply so that the audible
alarm may still be activated in the event of power or circuit failure to the navigation lights.

An ammeter (from Ampere Meter) is a measuring instrument used to measure the current in a circuit.
Electric currents are measured in amperes (A), hence the name. Instruments used to measure smaller
currents, in the milliampere or microampere range, are designated as milliammeters or microammeters.
Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of
the rotor and the stator slots of a Permanent Magnet (PM) machine. It is also known as detent or 'no-
current' torque.

1 msb safety all

2 battery order and specifications
3 parreling of generator..syncroscope speed
4 engine room crane safety..7 limit switch
5 motor getting overheating reason..fan and fins bta dena
Utsav H:
Int- rehman
Ext- basu
Function-5
1)Types of load, effect on msb by every type of loading, power factor,purely resistive load?
2) MSB safeties (operation, electrical), earth fault lamp, how to know,how it works, how to know
position of fault

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Electrical Oral

3) steering gear safety

4) lifeboat derric ELECTRICAL AND safety.
5) Difference between relay and switch.

Ayush Mishra:
Int.-new, Ext-mukherjee(sei)
1.Maintenance of starter panel of induction motor, cross-safety in starting panel and motor safety.
2.Bus bar ??Why on ship?How many in your ship, construction.
3.emergency generator solas regulation
4.how to order motor?
5.yad nhi h...

Func5
- brushless alternator
- inductance on induction motors
- fuses
- high voltage
Electrical..
AVR,e/r crane safety, how to check motor electrically, starters,iccp

Q1) motor got flooded with s.w, wht will you do. Cross question "why" for each step f.w cleaning,
heating etc, i.r not coming up after doing everything what can be the cause,(wanted to hear abt
detoriation of insulating material with heat and time)
Q2) clampmeter working, what current it will show in 3 coil and why
Q3) diffrence between 3 phase i.m and single phase motor
Q4) what is reverse power trip
Q5) how to confirm if shore supply is available, effect of incorrect phase sequence on motors, effect
of incorrect frequency on motors

Transformer,how many transformers on your ship? What are their types? Location ?Losses of
transformer? Why rating of transformer in kva and why not in kw?
Types of electrical load ?
Motor safeties,msb safties?
What is earth fault and how to detect it?
Ward lenard system explain in detail?

What is ACB? difference between acb and fuse?how to check if fuse is faulty ?
How to take generator on load in parallel?what to check?describe complete procedure and other
cross questions.
What is power factor?how much it was on your ship?what are the resons for low power factor?how
does it effect the system.

How to parallel generator? Why 11o'clock.

How does induction motor works.?

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Electrical Oral

What is power factor? What was on ship? What happens when pf is for eg.0.6?
Single phasing? Effects? Which trip?
One more simple ques. Got func 5.

Electrical

Transformer working principles and its losses? Cross - how many transformers used in the ship &
can we use two transformers at a time? If u use at a time, give reason & if we not use, give
reason?
Msb protection?
Three mode of starting for emergency generator? How much time it will take to come on load?
Starter? Type of starter? Explain
If battery is discarded? How you able to know that battery is discarded?
Got func 5!!

Electrical
Types of fuse and it's rating
How to parallel generator using lamp?
Indicators on emergency switch board
What is power factor and form factor? how we improve?
If battery is fully charged, then how will u know

Func 5
From where the current comes in the alternator when the ship is in blackout condition

Func 5
In your ship earth fault in 24V what will you do
How to know this earth fault
How many type of voltage i

Anchit Sahni:
Fn 5
Int skd ext Ram takla
1 msb safety all
2 battery order and specifications
3 parreling of generator..syncroscope speed
4 engine room crane safety..7 limit switch
5 motor getting overheating reason..fan and fins bta dena

1)Types of load, effect on msb by every type of loading, power factor,purely resistive load?
2) MSB safeties (operation, electrical), earth fault lamp, how to know,how it works, how to know
position of fault
3) steering gear safety

22
Electrical Oral

4) lifeboat derric ELECTRICAL AND safety.

5) Difference between relay and switch.

1.Maintenance of starter panel of induction motor, cross-safety in starting panel and motor safety.
2.Bus bar ??Why on ship?How many in your ship, construction.
3.emergency generator solas regulation
4.how to order motor?

Func5
- brushless alternator
- inductance on induction motors
- fuses
- high voltage

Electrical..
AVR,e/r crane safety, how to check motor electrically, starters,iccp

Transformer,how many transformers on your ship? What are their types? Location ?Losses of
transformer? Why rating of transformer in kva and why not in kw?
Types of electrical load ?
Motor safeties,msb safties?
What is earth fault and how to detect it?
Ward lenard system explain in detail?
What is ACB? difference between acb and fuse?how to check if fuse is faulty ?
How to take generator on load in parallel?what to check?describe complete procedure and other
cross questions.
What is power factor?how much it was on your ship?what are the resons for low power factor?how
does it effect the system.

Elec-
How to parallel generator? Why 11o'clock.
How does induction motor works.?
What is power factor? What was on ship? What happens when pf is for eg.0.6?
Single phasing? Effects? Which trip?
One more simple ques. Got func 5.

Electrical

Transformer working principles and its losses? Cross - how many transformers used in the ship &
can we use two transformers at a time? If u use at a time, give reason & if we not use, give
reason?

23
Electrical Oral

Msb protection?
Three mode of starting for emergency generator? How much time it will take to come on load?
Starter? Type of starter? Explain
If battery is discarded? How you able to know that battery is discarded?
Got func 5!!

Electrical
Types of fuse and it's rating
How to parallel generator using lamp?
Indicators on emergency switch board
What is power factor and form factor?how we improve?
If battery is fully charged then how will u know

Func 5
From where the current comes in the alternator when the ship is in blackout condition

ELECTRICAL
1.types of excitation sys.explain brushless.
2.battery maintenance.
3.star delta starter explain ,why ?

ELECTRICAL
1 Why starter is needed ?
2 thyristor (basic)
3 HIGH VOLTAGE adv( popular question now a days)
4 types of starters
Explain star Delta (dia)

5 induction motor
6 AVR working. N components
7 how to shut SCR ?
Wht if trigger voltage is reduced
8 air gap of AE ..how to take measurement of airgap ..n by which ?
9 what if generator is kept shut for long time ..how to start with battery
Where is that battery
10 any of excitation system

X QUESTION -

1 SCR need gate voltage .why ..

After applying gate voltage ..wht z d status of junction which was. reverse biased initially.
2 starter is used . Wht if use simple switch

3 in *∆ How it's connected in Delta later on.?

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Electrical Oral

4 why we need high voltage n above what value of voltage it z considerd HV onboard

That much x question only I remember .

Electrical
1) What is reverse power trip
Why is important
2) What are the equipments in which power is supplied by emergency generator

3) What is earth fault

How will you know there is earth fault
How will you know which equipment is effected
4) What do you understand by power factor
What are the different types of loads on ship
Which load effects power factor
5) What is single phasing
What will happen if equipment is run in such a case
Will the equipment start in case of such a fault

Electrical
-alternator maintenance.. Cross
-synchroscope
-paralleling
-photocell... Where used in ship( detector , flame eye)
-transducer

F5
1)dnt remember
2) cooling slots on a motor are chocked, what will be its effect and wht will you do
3) how to synchronise alternator with dark lamp method.( I completely told him opposite of it. I
told him bright lamp method)
4) wht is exciter, where it is usedThe main purpose of exciter in a generator(alternator) is to provide
stationary rotating magnetic field.Which isused to induce the e.m.f in the armature coil. So, DC power is
given to exciter and the exciter is nothing but a coil, and the exciter creates a magnetic field
definition: The system which is used for providing the necessary field current to the rotor winding of the
synchronous machine, such type of system is called an excitation system. In other words, excitation
system is defined as the system which is used for the production of the flux by passing current in the field
winding. The main requirement of an excitation system is reliability under all conditions of service, a
simplicity of control, ease of maintenance, stability and fast transient response.
5)how to reverse direction of rotation in single phase
Got function 3 safety.

Electrical
Ir test value of ir
Power factor n its effect

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Electrical Oral

Fuse types
Intrinsic safe circuit
Indicators on emergency switchboard

Result electrical

Electrical
1. How Gen works,x qus
2. Overhead crane safety
3. Battery- Lead acid
4. Transformer losses
5. Star-delta Starter.

EECEOL
1. Types of battery. Details of battery used on your ship (working and construction). How is
charging done.
2. Paralleling of generator requirement. Synchroscope working. 3 lamp method working.
3. Types of starters and their use. Reason and application.
4. Emergency generator power supply.
Eddy Current Loss
When an alternating magnetic field is applied to a magnetic material an emf is induced in the material
itself according to Faraday’s Law of Electromagnetic induction. Since the magnetic material is a
conducting material, these EMFs circulates currents within the body of the material. These circulating
currents are called Eddy Currents. They will occur when the conductor experiences a changing magnetic
field.

5. Megger working. How to megger test motor.

History of Megger
The device is being used since 1889, popularity raised during 1920s since the long back device is same in
its uses and purpose of testing, few real improvements appeared in recent years with its design and quality
of tester. Now high-quality options are available which are easy to use and quite safe.
What is Megger?
Insulation resistance IR quality of an electrical system degrades with time, environment condition, i.e.,
temperature, humidity, moisture and dust particles. It also gets impacted negatively due to the presence of
electrical and mechanical stress, so it’s become very necessary to check the IR (Insulation resistance) of
equipment at a constant regular interval to avoid any measure fatal or electrical shock.

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Electrical Oral

Uses of Megger
The device enable us to measure electrical leakage in wire, results are very reliable as we shall be passing
electric current through device while we are testing. The equipment basically uses for verifying the
electrical insulation level of any device such as motors, cables, generators, windings, etc. This is a very
popular test being carried out since very long back. Not necessary it shows us exact area of electrical
puncture but shows the amount of leakage current and level of moisture within electrical
equipment/winding/system.
Types of Megger
This can be separated into mainly two categories:-
1. Electronic Type (Battery Operated)
2. Manual Type (Hand Operated)
But there is another types of megger which is motor operated type which does not use battery to produce
voltage it requires external source to rotate a electrical motor which in turn rotates the generator of the
megger.

Electronic Type Megger

Important parts:-
1. Digital Display :- A digital display to show IR value in digital form.

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Electrical Oral

2. Wire Leads :- Two nos of wire leads for connecting megger with electrical external system to be
tested.
3. Selection Switches :- Switches use to select electrical parameters ranges.
4. Indicators :- To indicates various parameters status i.e. On-Off. For Example Power, hold,
Warning, etc.
Note: – Above construction is not similar for every megger, it difference appears manufacture to
manufacture but basic construction and operation are same for all.
Advantages of Electronic Type Megger
 Level of accuracy is very high.
 IR value is digital type, easy to read.
 One person can operate very easily.
 Works perfectly even at very congested space.
 Very handy and safe to use.
Disadvantages of Electronic Type Megger
 Require an external source of energy to energies i.e. Dry cell.
 Costlier in market.
Hand Operated Megger

Important parts:-
Analog display:- Analog display provided on front face of tester for IR value recording.
Hand Crank:- Hand crank used to rotate helps to achieve desired RPM required generate voltage which
runs through electrical system.
Wire Leads:- Used same as in electronic tester i.e. For connecting tester with electrical system.
Advantages of Hand Operated Megger
1. Still keeps important in such high-tech world as it’s an oldest method for IR value determination.
2. No external source required to operate.
3. Cheaper available in market.

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Electrical Oral

Disadvantages of Hand Operated Megger

1. At least 2 person required to operate i.e. one for rotation of crank other to connect megger with
electrical system to be tested.
2. Accuracy is not up to the level as it’s varies with rotation of crank.
3. Require very stable placement for operation which is a little hard to find at working sites.
4. Unstable placement of tester may impact the result of tester.
5. Provides an analog display result.
6. Require very high care and safety during use of the same.
Construction of Megger
Circuit Construction features :-

1. Deflecting and Control coil : Connected parallel to the generator, mounted at right angle to each
other and maintain polarities in such a way to produced torque in opposite direction.
2. Permanent Magnets : Produce magnetic field to deflect pointer with North-South pole magnet.
3. Pointer : One end of the pointer connected with coil another end deflects on scale from infinity to
zero.
4. Scale : A scale is provided in front-top of the megger from range ‘zero’ to ‘infinity’, enable us to
read the value.
5. D.C generator or Battery connection : Testing voltage is produced by hand operated DC
generator for manual operated Megger. Battery / electronic voltage charger is provided for
automatic type Megger for same purpose.
6. Pressure Coil Resistance and Current Coil Resistance : Protect instrument from any damage
because of low external electrical resistance under test.
Working Principle of Megger
 Voltage for testing produced by hand operated megger by rotation of crank in case of hand
operated type, a battery is used for electronic tester.
 500 Volt DC is sufficient for performing test on equipment range up to 440 Volts.
 1000 V to 5000 V is used for testing for high voltage electrical systems.

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Electrical Oral

 Deflecting coil or current coil connected in series and allows flowing the electric current taken by
the circuit being tested.
 The control coil also known as pressure coil is connected across the circuit.
 Current limiting resistor (CCR and PCR) connected in series with control and deflecting coil to
protect damage in case of very low resistance in external circuit.
 In hand operated megger electromagnetic induction effect is used to produce the test voltage i.e.
armature arranges to move in permanent magnetic field or vice versa.
 Where as in electronic type megger battery are used to produce the testing voltage.
 As the voltage increases in external circuit the deflection of pointer increases and deflection of
pointer decreases with a increases of current.
 Hence, resultant torque is directly proportional to voltage and inversely proportional to current.
 When electrical circuit being tested is open, torque due to voltage coil will be maximum and
pointer shows ‘infinity’ means no shorting throughout the circuit and has maximum resistance
within the circuit under test.
 If there is short circuit pointer shows ‘zero’, which means ‘NO’ resistance within circuit being
tested.
Work philosophy based on ohm-meter or ratio-meter. The deflection torque is produced with megger
tester due to the magnetic field produced by voltage and current, similarly like ‘Ohm’s Law’.
The torque of the megger varies in a ration with V/I, (Ohm’s Law:- V = IR or R = V/I). Electrical
resistance to be measured is connected across the generator and in series with deflecting coil.
Produced torque shall be in opposite direction if current supplied to the coil.
1. High Resistance = No Current :- No current shall flow through deflecting coil, if resistance is
very high i.e. infinity position of pointer.
2. Small Resistance = High Current :- If circuit measures small resistance allows a high electric
current to pass through deflecting coil, i.e. produced torque make the pointer to set at ‘ZERO’.
3. Intermediate Resistance = Varied Current :- If measured resistance is intermediate, produced
torque align or set the pointer between the range of ‘ZERO to INIFINITY’.

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Electrical Oral

Connection Diagram of Megger for Testing

6. Current transformer working and application

Definition
A current transformer is an instrument transformer, used along with measuring or protective devices, in
which the secondary current is proportional to the primary current (under normal conditions of operation)
and differs from it by an angle that is approximately zero.
Functions
Current transformers perform the following functions:
 Current transformers supply the protective relays with currents of magnitude proportional to
those of power circuit but sufficiently reduced in magnitude.
 The measuring devices cannot be directly connected to the high magnitude supplies. Hence
current transformers are used to supply those devices with currents of magnitude proportional to
those of power.

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Electrical Oral

 A current transformer also isolates the measuring instruments from high voltage circuits.
Principle
The basic principle of the current transformer is the same as that of the power transformer. Like the power
transformer, the current transformer also contains a primary and a secondary winding. Whenever an
alternating current flows through the primary winding, alternating magnetic flux is produced, which then
induces alternating current in the secondary winding. In the case of current transformers, the load
impedance or “burden” is very small. Therefore the current transformer operates under short circuit
conditions. Also the current in the secondary winding does not depend on load impedance but instead
depends on the current flowing in the primary winding.
The current transformer basically consists of an iron core upon which primary and secondary windings
are wound. The primary winding of the transformer is connected in series with the load and carries the
actual current flowing to the load, while the secondary winding is connected to a measuring device or a
relay. The number of secondary turns is proportional to the current flowing through the primary; i.e., the
larger the magnitude of current flowing through the primary, more the number of secondary turns.
The ratio of primary current to the secondary current is known as the current transformation ratio of the
CT. Usually the current transformation ratio of the CT is high. Normally the secondary ratings are of the
order 5 A, 1 A, 0.1 A, whereas the primary ratings vary from 10 A to 3000 A or more.
The CT handles much less power. Rated burden can be defined as the product of current and voltage at
the secondary side of the CT. It is measured in volt ampere (VA).
The secondary of a current transformer should not be disconnected from its rated burden while current is
flowing in the primary. As the primary current is independent of the secondary current, the entire primary
current acts as a magnetizing current when secondary is opened. This results in deep saturation of the
core, which cannot return to normal state and so the CT is no longer usable.

32