Interview Questions Answers in Electrical Engineering

Question { 2978 }

how the transformer stables out zone faults? Because we use
non directional O/C relays .Is there any special
considerations are taking into account to overtake this?

Answer

directional relay only used if system is Parallel or Ring,

Is This Answer Correct ?

0 Yes

0 No

Question { L&T, 6783 }

What is the clear distance between a MV panel(rear side) and wall.

Answer

refer to IEC about AFLR, it require 900mm minimal for rear side clearance and 1300mm for front panel clearance, and 600mm for ceiling

Is This Answer Correct ?

0 Yes

0 No

Question { CS, 4441 }

how we calculate the knee point of a protection and metering
CT and what is the testing procedure.

Answer

knee point voltage is only for protection, not for measurement, it is depend on your protection you need,for example, 87 need higher Vkp than 50/51, just follow your relay requirement. I mean your CT Vkp should higher than Relay required Vkp. refer to IEC, for class 5P or 10P, Vkp is as a function of ALF, Rct, VA, and secondary ratio of CT

Is This Answer Correct ?

0 Yes

1 No

Question { GE, 3380 }

What iz main protection of mediuum voltage motors and what
iz the standard IR voltage of 6.6 and 11kv motors.

Answer

27,46,49,50,51,50N,51N,51LR,66,87M(OPTION)

Is This Answer Correct ?

0 Yes

0 No

Question { Hindustan Unilever Limited, 7427 }

Dear Sir / Madam,

Actually we requied 64 A MCB,

But i have 32 A MCB = 2 No's

this two i have to make series connection and we usw any
place?

isit possible or not......

Answer

you can do that, but in parallel. not in series

Is This Answer Correct ?

3 Yes

0 No

Question { 4469 }

what will happen if the connections of protection ct reverse?
will it burn the ct?

Answer

if your protection is only 50/51 there will be no effect,
but if you enable function of 32,67, and 87T, relay goes to malfuntion

Is This Answer Correct ?

0 Yes

0 No

Question { 3152 }

what types of fault occurred in transmission
line ?
which protection function senses the fault?

Answer

in common practice of transmission line, 90% of failure is subtranstien type caused by nature

Is This Answer Correct ?

0 Yes

1 No

Question { 2735 }

can we use ps class in combination with protection class in
differential protection and over current protection.

Answer

yes ofcourse, i already experienced this case

Is This Answer Correct ?

0 Yes

0 No

Question { 8697 }

if you asked to choose a ckt breaker from MCB & MCCB for 32A
which one will be best and why??

Answer

according to my experience, if load continuous current less or equal than 60A, it is better to use MCB, it is easy to install and cheaper. you can select MCB tripping class A,B or C depends on your application.

Is This Answer Correct ?

0 Yes

0 No

Question { ERL, 5337 }

In CT, burden is 15 VA and protection 5P20,CT ratio is 100:1
then what would be the knee point voltage ?

Answer

for class 5P, Vkp is function of ALF,Rct, secondary ratio, and Rated burden, we need to know the Rct(CT resistance)

Is This Answer Correct ?

0 Yes

0 No

Question { 4650 }

In a 132KV Grid Station where voltage level is 132KV, here, why the rating of Surge arrests installed 120KV ?

Answer

it depends on grounding method,

Is This Answer Correct ?

4 Yes

2 No

Question { 3490 }

what is the best way to start a 15 KW motor for pump star-delta or direct on line ?
and from how many KW i must use direct on line ?

Answer

15kW motor is small load categorized, DOL will be the best choise, you need at least 6 to 8 times of kW at motor starting

Is This Answer Correct ?

1 Yes

1 No

Question { 5625 }

how to calculate KA rating of C.B?explain with Formula.

Answer

Breaking capacity of CB is more than fault current main busbar

Is This Answer Correct ?

2 Yes

0 No

nur asidik