Interview Questions Answers in Electrical Engineering

How do you maintain the earthing resistance?

Answer

dont just add water and salt it is very boring, add some curry powder and meat as well it will be more spicy.
the best solution would be to add more earth pits in parallel till you get your targeted resistance reading or lower.

Is This Answer Correct ?

15 Yes

10 No

Question { 6124 }

In a parallel circuit dc circuit with two resistors, if you
know the voltage, amperage, and one resistors ohms, what
formula is used to find the second resistors ohms?

Answer

use only ohms law.

Is This Answer Correct ?

0 Yes

1 No

Question { Greeves, 87277 }

How to calculate the diesel generator efficiency? what
details are required to identify the running diesel
generator sets with 1000 kVA & 180 kVA?

Answer

You did not say what efficiency, whether you get good KWH/ diesel consumption or whether the genset is loaded efficiently
Whatever, you need a KWH METER AND DIESEL CONSUMPTION METER.If you run your 1000KVA gen set for 20 hrs.your genset say at 0.8 pf it could have generated;
1000kva x 0.8 =800KWH per hr .SO FOR 20 Hrs s 16000KWH. If YOUR KWH generated reading says 12000kwh than your generator usage effiociency is 12000/16000 =75%
If the diesel consumption was 600ltrs than kwh/l is
12000/600 =20KWH/Litre diesel. you have to calculate seperately for both of them.

Is This Answer Correct ?

36 Yes

34 No

Question { 3502 }

Can a 5 core cable one end with a 32A 3p+N+E plug and the
other end 32A 3p+E be used on a generator?

Answer

Can !THE END CONNECTED TO THE GENERATOR IS A 32A 3P+E than
at the other end do not connect the a load with a neutral
connection.If you are going to connect to a 3 ph motor or any
other load that does not require a neutral it is absolutely
safe

Is This Answer Correct ?

4 Yes

0 No

Question { TCS, 3932 }

What is the 415V AC Soft starter? Explain with an example?

Answer

A soft starter is actually an electronic motor
starter.Instead of using a star delta or a auto transformer
or rotor resistant starter where with the aid of cont actors
and the devices the starting current is reduced to prevent
damage to the motors the machines driven by them or prevent
interruption to the power supply.
The soft starer does the same job but with the advantage of
you being able to preset the starting time and the starting
current consumption.You will be able to determine how much
torque can be given for the starting, but once the starting
is done the soft starter is excluded from the circuit WITH
THE HELP OF A BYPASS CONTACTOR but sometimes maintained just
for monitoring.

Is This Answer Correct ?

5 Yes

0 No

Question { 15136 }

Can anyone tell me how a 12v battery is transformed to
20,000v at the spark plug

Answer

Umesh is right.The 12 volts is connected to an ignition coil (STEP UP TRANSFORMER)through a switch (CONTACT POINTS OR DISTRIBUTER) when the switch is INTERRUPTED a high voltage is created (ONLY ONCE FOR EACH INTERRUPTION) according to the design of the ignition coil.

Is This Answer Correct ?

5 Yes

0 No

Question { 8637 }

I have recently seen a transformer which had two primary
terminals and was connected between two lines,i would like
to know what kind of transformer is it?short discription
about it,any advantages,purpose of usage of the
same.............

Answer

please give more relevent details. how you guess it is primary terminals ,how many phase. used where .how many kva .the secondary connected where, how many volts.without some guiding information nobody can really help, every body can just guess something and in the end nobody benefits.

Is This Answer Correct ?

1 Yes

0 No

Question { HP, 4902 }

What is transformer break down voltage.And what is flash
oil flash point.

Answer

It is transformer oil dielectric breakdown voltage.
A sample of the tx oil is collected and tested with a
special tester. In the tester is a pair of electrode spaced
as per BS
spec. A TEST VOLTAGE IS APPLIED ACROSS THE ELECTRODES , and
this voltage is gradually increased until a breakdown
happens resulting in sparks across the electrode, immeadetly
the test voltage is stoped and the RMS voltage is
calculated.A few test is carried over and the mean voltage
is taken as the breakdown voltage of the sample oil under
test.

It is flash point of oil.The flash point is at what temp the
oil would self ignite. This depends on the quality and type
of oil.

Is This Answer Correct ?

2 Yes

0 No

Question { ABB, 16055 }

if we convert ampers into kw,which one formula use by
us,pls tell me?

Answer

there is no one formula only.
there are some formulas that you must know,,
you must know how to use the correct one when you need it.

for DC power it is always just voltage x current = watts

for AC single phase it is always volt x current x pf = watts

for AC 3 phase it is root 3 x volt x current x pf = watts

the watts than you change to KW or MW if necessary.
this are all for real calculations. when you practice with it often than you will be able to give an estimate bcos the pf varies according to situation.

Is This Answer Correct ?

6 Yes

0 No

Question { 7068 }

What is the diffrence between an ELCB(earth leakage circuit
breaker) and RCCB(residual current circuit breaker)?which
has higher degree of safety and why?

Answer

ELCB is voltage based sensing device.If the leakage voltage is above 40 v(usually) it will trip.
RCCB is current based sensing devise. If the leakage current is above the stated amount it will trip.(U CAN BUY DIFFERENT VALUES from 5 milliamps to 300 milliamps)
RCCB has a higher level of safety because even if the leakage current did not get to the earth by the normal circuit maybe because the earth wire was not connected or loose but passed through somebody and than to the ground the rccb will still trip if the current is above the milliamp rating.

Is This Answer Correct ?

8 Yes

2 No

Question { 7040 }

what is the function of buchhos rely in transformer

Answer

It is known as BUCHHOLZ relay.
A buchholz relay is operated by the accumulation of air bubbles within a transformer.
a) When a short circuit happens within the windings or within the contacts of the tap changer or any other shortings a localised heating takes place and gasses are liberated within the transformer.
b) When there is a leak in the transformer and the oil level drops or
c) The temp drops too low and the oil level falls below the required level.
These conditions trigger the float switch within the buchholz relay. The contacts are used for tripping the transformer or to on an alarm.

Is This Answer Correct ?

0 Yes

2 No

Question { 6685 }

OUR METER READER TAKE READING OF INDUSTRIAL CONSUMER.THEY
ALWAYS ASK HOW TO INCREASE POWER FACTOR FROM 60% TO 99 % TO
AVOID PENALTY OF POWER FACTOR.

Answer

The power factor is low for industrial customer because the load is usually inductive due to the many motors installed.
Power supply companies sell by calculating KWH used.Thier generators maximum capacity is limited by the amps the generator can produce at a fixed voltage.
So calculations will tell u that lower power factor means higher amps for the same KWH &AND HIGHER PF MEANS LOWER AMPS for the same kwh. thus the power supply companies can make more money from the same generator and also save on other expenses.
power factor is improved by connecting reactive load in parallel.this reactive power is loss free and you dont pay for the power consumption.

Is This Answer Correct ?

2 Yes

0 No

Question { 5541 }

can we use 7volt DC BATTERY to run a 60watt motor by
stepup? Give reason for your answer?

Answer

can.
Because 60 watts motor consume 60/7 = 8.5 amps. Now if your motor is rated to run at 7 volts and your battery is big enough to give 8.5 amps than no problem.

Is This Answer Correct ?

2 Yes

2 No

Question { 3474 }

when the PFR (POWER FACTOR REGULATOR)change a step to
zero,one of the RCCB will triped off,is it the changing step
of this PFR effect the RCCB?

Answer

what is a RCCB doing inside a PFR. Any way if a rccb trips
than it means there is a earth leakage.otherwise the wiring at
the PFR is wrong especially the neutral connections or the
RCCB itself is faulty. Check all the wirings first and than
try substituting the RCCB itself

Is This Answer Correct ?

0 Yes

0 No

Question { 3474 }

when the PFR (POWER FACTOR REGULATOR)change a step to
zero,one of the RCCB will triped off,is it the changing step
of this PFR effect the RCCB?

Answer

Is This Answer Correct ?

0 Yes

0 No

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