Question { Birla, 3581 }

what is the difference in operation of 3 phase motor when am
forward delta connection and reverse delta connection?

Answer

Direction of speed

Induction motor runs in forward direction with forward delta
connection, where as it is vise verse for reverse delta
connection.

Question { 5264 }

If the circuit breaker will not close or it will trip, what
will you do?

Answer

I can follow below trouble shooting steps,

check the error code to see if there was any short ckt or
earth fault, if there was (check for cable termination if
the connections are not burnt out due to short circuit,
check earth resistance and current voltage etc. of the
terminals) eliminate the fault then it should work fine.
Check the control wiring of the breaker check the fuses,
contactor operations etc.

check the under voltage release to see if it did not trip
due to under voltage or over voltage. check shunt trip
mechanism.
check if breaker is not overheated as a breaker may not
close if magneto thermal release is tripped.

check closing coil operation and see whether breaker gets
charged automatically with help of the motor.

if none of the above problem found, Rack out the
breaker(keep it in isolated position)trip the breaker
manually a few times and try closing it again should work fine.

In case it does not happen you can try and by pass the
breaker with help of crocodile pin Jumpers ( In case of
Emergency), but one need to be extremely careful and should
ensure that the incomer supply to breaker is turned off
while doing it, as a high risk is involved. Also you should
be confident that breaker did not trip due to an abnormal
condition.


Note: Some breakers indicate nuisance fault as well

Further,

Question { HAL, 8738 }

How can we select a capacitor Bank.? i need a standard
formula for that.?

Answer

kvar = kw(tanø1 - tanø2)

where ø2 is the existing power factor and

ø1 is the desired power factor.

Question { 5429 }

how much current will be drawn by 3 phase, 415v, 50 hz, 20
ton central ac

Answer

One Toe = 3.5 kw

20 * 3.5 = 70 kw

P = 1.732 * v * I * cos0

70000 = 1.732 * 415 * I * 0.8

I = 122 A

Question { 6522 }

what is mean by harmonics?Type of harmonics?

Answer

Harmonic is presence of unwanted frequencies.
Few types of harmonics are listed below. these frequencies mainly gets generated due to modern electronic equipment e.g
Computer, inverters etc.

3rd level harmonics
5th level harmonic
7th Level Harmonic
11th level harmonics
13th level harmonics

3rd level harmonic is normal, however when it goes up to 5th or 7th it's considered a problem.
11th and 13th level harmonics usually found where rectifiers and DC loads are connected.

Question { Trimax, 3490 }

what is mean Boost voltage and what is working principle of Tube light

Answer

to add to it 1000v is applied across th tube light to ionise halogen particles

Question { 5144 }

why we are using (-24VDC) and where we r using plz tell me

Answer

In telecom Industry, Telecom devices use -24 Volts DC, as positive terminal is grounded.

Question { 5144 }

why we are using (-24VDC) and where we r using plz tell me

Answer

-24V DC is used for Telecom server and equipment, as positive terminal is grounded.