Interview Questions Answers in Electrical Engineering

what is RMU ?

Answer

RMU stands for Ring Main Unit having at least three
switches ( Breaker or isolator os load break switch)
connected with a bus with mechanical interlocking as per
system requirement.It can used upto 11KV with bus loading
capacity 630 A . Breaker may be of rating 200A or 630A as
per requirement. Two LBS can be used as two I/C and CB as
out going feeder or DT feeder as per requirement. In this
way O/G or DT feeder can be feed through second I/C if
supply from first I/C intruppted due to any reason. So RMU
reduce the supply ontrupption time.Many RMU's can be
connected in a ring mode in a distribution system.

Is This Answer Correct ?

7 Yes

0 No

Question { 9031 }

6 MVA transformer secondary is rated for 725V at no load.
The incommer ACB is rated at 690 V, 3200 Amp. Would there
be any effect on performance of ACB due to lower voltage
rating?

Answer

ACB is not suitable as transfomer secondary voltage level
is higher than ACB voltage level which cause insulation
failure of the ACB and cause of flash.

Is This Answer Correct ?

0 Yes

0 No

Question { MNC, 117961 }

What are the voltage values for LT,HT,EHT and other
voltages??

Answer

It depands on the system. 433V (Phase to Phase) from
transformer 11000/433V is LT voltage and 11000V(phase to
phase) from 33KV/11KV to transformer 11000/433V is HT
voltage whereas 33KV is EHT voltage level.

Is This Answer Correct ?

10 Yes

4 No

Question { 4168 }

WHAT IS THE REASON FOR LOW VOLTAGE IN HOUSES?*

Answer

Reason for Low voltage in houses are as under
1. High volatge require heavy insulation for all house hold
electrical appliances that cause more bulky and expensive
electrcal appliances.

2.If power is assumed to be same for both the cases than
high voltage system will not cater for heavy load as low
voltage system means less number of consumer can be
supplied with same power and may say that there will be
heavy power loss.

Is This Answer Correct ?

1 Yes

0 No

Question { 4150 }

Waht are the protection should be use in HT/ LT side of the
same Xformer?

Answer

HT side
Over current protection
Short circuit protection
Earth fault protection
Differential protection
Transformer trouble protection

LT Side
Over current protection
Short circuit protection
Earth fault protection

Is This Answer Correct ?

4 Yes

0 No

Question { 8942 }

what will happen if transformer given dc input

Answer

If DC is applied to transformer its winding will act as
source of unidirectional flux which causes core saturation
(if DC supply of sufficient magnitude is applied
continuosly).Thee will not be indused EMF in either
winding.Due to this reason transformers are not used in DC
supply .

Is This Answer Correct ?

2 Yes

0 No

Question { 6656 }

exact difference between electronicsand electrical

Answer

Electronic means micro control of movement of electrons and
holes where as electrcal means macro control of high
speeded elecrons in a conductor. In electronics one can
control the speed of electron as per requirement but in
electrical one can only switch the motion of the electron.

Is This Answer Correct ?

1 Yes

0 No

Question { 24371 }

what is the purpose of CT,PT

Answer

CT is a current instrment Transformer. It is used to
linearly step down the primary current as per the rated
current of controlling device attached with. It is used as
current sensor.

PT is a potential instrument transformer . It is used to
linearly step down the primary voltage as per the rated
voltage of controlling device attached with. It is used as
voltage sensor.

Is This Answer Correct ?

3 Yes

7 No

Question { 6483 }

I have current, kva How can calculate kv?

Answer

kv=kva/a

Is This Answer Correct ?

2 Yes

0 No

Question { 5580 }

what happens if DC earthing and AC earthings are shorted?

Answer

Nothing happen if earthing is firm otherwise AC and DC will
mix and give unwanted wave shape and it will be harmfull if
that wave shape is significant for the system .

Is This Answer Correct ?

7 Yes

0 No

Question { CECRI_Central_Electrical_Research_Institute, 12294 }

1. which type of transformer connection is preferred in
case of power supply transformers?
(A) Star/Star
(B) Delta/Delta
(C) Star/Delta
(D) Zig Zag/Star
2. In a power transformer usuall which winding is closer to
the core?
(A) Primary winding
(B) Secondary winding
(C) Low Voltage winding
(D) High Voltage winding
3. The power factor of a purely inductive load is
(A) Zero
(B) Lagging
(C) Leading
(D) Unity.

Answer

1. Star/Delta Type of transformer connection is preferred
in case of power supply transformers.

2. In a power transformer usually Low Voltage winding is
closer to the core

3.The power factor of a purely inductive load is Lagging

Is This Answer Correct ?

2 Yes

4 No

Question { 46010 }

what is a bus riser in power system and why it is used

Answer

Bus riser is used in between two buses at same level
connected with a circuit breaker called bus coupler.In this
system one bus is connected with upper portion of the
breaker and lower portion or output of circuit breaker is
connected to bus riser who works to rise the bus on level
of first one.

Is This Answer Correct ?

32 Yes

10 No

Question { 5799 }

what is the difference between analog and digital signal?

Answer

Analog signals are dynamic in nature means they are
continuous. Magnitude of the signal may change in fraction
as well as abruptly.
Whereas digital signals are static in nature means they are
not continuous .Magnitude of digital singnals may either be
High (1)or low (0).

Is This Answer Correct ?

2 Yes

0 No

Question { 5504 }

why we are called the 4-20ma transducer,not 0-20 ma
transducer??

Answer

4mA is the minimum operating current of controling device

Is This Answer Correct ?

2 Yes

0 No

praveen gupta