Interview Questions Answers in Electrical Engineering

What is mean CT Saturation? How to calculate?

Answer

according to me, almost answers are correct,
in my understanding CT saturation is expressed by knee point voltage for class X, class 5P or 10P CT.

Is This Answer Correct ?

3 Yes

5 No

Question { 19701 }

A 3 phase motor, 440 voltage, induction motor. If we take
out rotor from motor and if we give supply 440 volt to
stator then what happens?????

Answer

in practice, stator will heat up because of losses,

Is This Answer Correct ?

0 Yes

0 No

Question { 3837 }

CAN A CD/CLOCK RADIO WITH 110V 60HZ WORK ON A 110V 50HZ
FEED.

Answer

yes you can, but for several time you device will get heating up

Is This Answer Correct ?

0 Yes

0 No

Question { 18444 }

which type of breaker sould be used for different level of
voltage ? (i.e at 11 Kv, 33 Kv, 66 Kv....

Answer

below 36kV, it is better to use VCB, and above 36kV to use SF6

Is This Answer Correct ?

1 Yes

0 No

Question { 9578 }

How can I communicate with an Areva MiCOM P121 relay by
RS485 port? In other word, which command can I send and
what information can I have recieved? please send some
refrences, please. thanks

Answer

all micom series compatible for mudbus RS485 as basic communication protocol,

Is This Answer Correct ?

0 Yes

0 No

Question { wbsedcl, 17553 }

what type of protection used below 132KV feeders

Answer

27,46,50,51,50N,51N,64REF,79,87T+L

Is This Answer Correct ?

0 Yes

0 No

Question { 6337 }

Two CTs 1600/1 and 35/1 are in series. while checking the
ratio test of a CT(1600/1),same 1600A will also pass
through the CT having ratio 35/1.
Will it be harmfull to the ct(35/1),if yes , what will
happen.CT secondary is shorted

Answer

refer to IEC, CT can withstand for 1s if current at primary is 1000xIn, mean 35kA is maximal. saturated or not is depend on Rct and burden, need to be calculated

Is This Answer Correct ?

0 Yes

0 No

Question { L&T, 10571 }

What voltage is used in Directional earth fault relay? and
why?

Answer

to make polarisation

Is This Answer Correct ?

0 Yes

1 No

Question { 2848 }

6.6Kv feeder feeding tow step down transformers-415V-,what
the possible consideration for parrellel operation?

Answer

Rating and vector clock of TR

Is This Answer Correct ?

0 Yes

0 No

Question { 2273 }

How many types of Differential protection are there?
and what the special arrangement are made at the time of
charging of a transformer on the Differential protection?

Answer

in fact, there are two.
-lowZ
-Hiz

2nd harmonic blocking should be employeed to prevent relay trip during Tr stating up,

Is This Answer Correct ?

0 Yes

0 No

Question { 7676 }

why most of the induction are delta connected?

Answer

because almost load driven by motor is low power such as pump, so it safe to use delta starting

Is This Answer Correct ?

0 Yes

0 No

Question { 3257 }

why we are using the 2 slope in differential relay?but in
busbar differential we are using only one slope.
what is the reason.

Answer

-on lowZ differential, when fault happens, CTs going to go saturated. slope aims to compensate error due to CT saturation because CTs have different characteristic.
-for busbar protection, it is HiZ differential, one slope because all CTs have same charracteristic. no need to compensate

Is This Answer Correct ?

0 Yes

0 No

Question { 2513 }

Can we use Motor protection CB while we use the VFD for
Speed control?? if not means please tell the reason!!!

Answer

i already have had project with the same case, no problem,

Is This Answer Correct ?

0 Yes

0 No

Question { L&T, 5195 }

how to calculate restraing current and operating current
for differential protection if 20 mva transformer is OLTC
33 kv/11 kv ? and what should be the type and ratio of CT?

Answer

let call Irestrain as Itot, because different relay have different characteristic to define Ires.
for micom P54x, Itot =(|I1|+|I2|)/2,
for sepam T87, Itot =Max(|I1|,|I2|)
where I1=primary current
I2=secondary current,
it need to be consider to calculate transformer ratio factor

Is This Answer Correct ?

1 Yes

0 No

Question { 2515 }

Can anyone send details regarding motor protection relays ?
their manuals please ?

Answer

you can refer to Micom P24x or sepam M4x

Is This Answer Correct ?

0 Yes

0 No

nur asidik