Interview Questions Answers in Electrical Engineering

Questions / { sasi karthick a }

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Answers / { sasi karthick a }

What is the power ratio between power in Star and Delta
circuit?

Answer

The power is depends on the resistance of the winding. Lets
Take "R"ohm resistance of winding and connect in star
configuration.

then transform it to delta. You will see the result. It
will "R/3". So low resistance, high current, power.

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Question { 6485 }

how system voltage affect the power factor or vice-versa.

Answer

PF is purely depends on the load. If the connected load is
more inductive then it requires potential difference to
store the energy in form of magnectic flux which is not
useful work to load. Hence the voltage lags behind the
current until the inductance is fully stored.

If more inductance leads to more lagging leads to (cos
) will be low hence voltage will drop more, since the
actual voltage spiltted for magnectising and work done.

Appropirately current will raise.

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Question { 11313 }

What is the use of Isolation Transformer, and Neutral is
using for return path, finally this current is going....
but same time the voltage of the neutral should be below 1
V...

Answer

Isolation transformers are used to isolate the two sides of
the system with respect to electrical and introducing a
transformer will bring down the short circuit fault level
because of transformer impedance.

Tats y lighting transformer are considered even though for
same level of voltages.

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Question { 10867 }

MCB is used for high rating &MCB is used for lower
rating.What is technical difference between ACB & MCB?

Answer

MCB is for lower voltage and lower currents. MCB short
circuit current level is 10kA only.

ACB is ever for lower and medium voltage and high currents.
Short circuit, making and breaking currents are so high.

Both are using air for quenching medium.

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Question { 3895 }

the resistance of wire having length X M is R OHEM if i
streched the wire to dubble length what will be the
resitance

Answer

Not exactly, while streching the wire not only the length
but cross sectional area also changes. So it also depends
on both after streching.

Since R=(pl)/A.

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Question { 14666 }

Why Two Transformers aside shoud be supperated by concreted
wall?

Answer

It is fire wall, during fault condition if transformer at
fire it should not spread to other equipment/buildings.

As per IS, the thickness should be 350mm brick wall/230mm
concrete wall. Height of the wall shall be decided based on
the height of x'frm

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0 No

Question { 12628 }

Explain the Term in CT Name Plate – Class: 5P10

Answer

It defines tat, at 10 times (During fault condition) of the
rated current of CT the accuracy shall be +/-5%.

for more, plz refer is-2705 part-1 to 4, ETD-34.

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Question { Reliance, 4799 }

why the weight of oil in transformer is specified (on the
nameplate) in litres as well as kilo grams?

Answer

Liters is mentioned for quantity where weight in kg
mentioned for load details during foundation design.

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Question { 7525 }

For a CT the number of turns in the primary winding is.........

Answer

One

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Question { 8328 }

what will be the motor terminal box connection arrangement
(star or delta). on what basis it decided?

Answer

it is standard 6 terminal with 3Starting and 3ending points
of windings. Plz refer the below link for connection
diagram.

for low voltage motors,
Upto 2HP/1.5kW - star
above 2HP/1.5kW - Delta

With the same winding, power of the motor varies 3:1 ratio
in Delta to star.

http://www.elprocus.com/wp-
content/uploads/2013/09/Induction-motor-winding-terminals-
connected-in-star-and-delta-configuration.jpg

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1 Yes

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Question { Allied Group, 4723 }

different between horse power and break horse power

Answer

I think the HP is net power generated in motor and BHP
means after transmission of power at end of the shaft.

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Question { 5851 }

why is a earth pit 10 ft usually? And, what should be the
distance betweeen two earth pit?

Answer

Resistivity of the soil will better when depth increases.
Soil resistivity test will conduct and the resistivity will
selected for earthing calculation. As per IS 3043, it
should be twice the length of the electrode.

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1 No

Question { Siemens, 9592 }

what happens when we apply dc to a transformer

Answer

Inductive reactance is zero since F=0; high current pass
thru', windings may damage/burn. And ofcource no mutual
induction.

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Question { PSU, 4407 }

in india are trains run by DC or AC? if DC ,

from where it receives negative potential? because
pentograph receives singe potential only?

Answer

Train receives 25kV Ac line only. Inside rectifier convert
ac to dc.

Is This Answer Correct ?

2 Yes

3 No