Question { 5511 }

What will be the average KVA rating of Auto Transformer
for 75kw 415V , 3phase induction motor

Answer

motor rating in kva = 75/0.5=150kva
so the apparent power is let 200kva.
Keeping the starting condition and fault conditions like
overload,single phasing etc. I suggest 200x3=600kva or
750kva a standard value for the motor of 75kw,supposing that
transformer ration is 1:1.

Question { TATA, 10051 }

why we are using DC supply in megger?

Answer

As we know DC current is uni-directional.The deflection
system attached to the megger is generally PMMC type which
eorks only with DC. Another reason is when DC current flows
in the winding of a motor or transformer the capacitance and
inductance do not act upon the current and the only leakage
current that flows through the insulation is measured.This
gives faster and accurate measurement.If we use an AC megger
the reading will be erroneous because the capacitance of
winging will allow to flow high current and breakdown of
insulation will not occur due to alternating action of
current.

Question { 21294 }

What shocks us ,
Current or voltage?

Answer

The correct answer is current because when only current
flows in our body, the electrons also flow in our body and
they cause the red blood cells to puncture and damage the
plasma of our body.This causes shock and we loose our
feeling or sensation.Voltage or potential difference causes
the current flow but current gives us shock.It is known
that without voltage current can not flow.So voltage is the
source and current is the cause.

Question { 4215 }

in 3 phase induction motor resistance value is how much

Answer

In any motor the resistance value depends upon its kilowatt
rating. you can calculate the value or measure with a
multimeter.

Question { L&T, 18512 }

What is the problem, if a circuit breaker is not closing.

Answer

1. spring may not charged. control supply may missing.
breaker is not at service position.trip is activated or any
external interlock inhibiting the switching.
2. no
3. to save the breaker
4. for human safety.