Question { NTPC, 5544 }

How much duration I can keep open the CT if it is under
loading condition(100 Amp load)?

Answer

when ct is open circuited there is more voltage at the open
ends. this voltage may dangerous, if touch it you feel
sevior shock. The ct turns will act secondary itself & the
voltage will be equal to
voltage at bus or cable X No.of turns of the ct
which leads to leathal voltage & the current path is open
thus circuit is not completed.We aRE using ct's for metering
& protection. The metering ct will not get saturarated after
its rated VA immidiately but the protective ct's are GET
saturarated after its rated VA.

Question { 6423 }

how can we calculate ct ratings ?its any formula ?

Answer

we calculate ct rating not by turns ratio factors considered
are application & va required. You need 5A OR 1A secondary
of ct. Generally we use in ht side 1A CT's & 5A CT'S IN LT SIDE.
Application means Metering or ProtectionIf you dont know
please read the name plate of CT's

Question { BEL, 5305 }

What is Procedure the procedure to select CT's & PT's in
66kV and above substation?

Answer

The above answer is correct , the procedure is same in
selecting 6.6kv also

Question { Aditya Birla, 8572 }

What is pole slipping relay? When it is operated?

Answer

when angular displacement of the rotor exceeds the stability
limit then rotor slips a pole pitch or we can say rotor flux
slips with respec to rotor flux. this is called pole
slipping .This relay is or protection used in generators. It
needs long explanation please refer the books

Question { 13353 }

WE HAVE A LOAD OF 55KW MOTOR ITS VOLTS 380 3PH AND ITS
TAKING 100AMPS (ITS FULL LOAD IS 105AMPS)AND ITS CABLE IS
4CX50SQMM ,NOW ITS GETTING ABNORMAL HEATUP IN CABLE,PLZ
TELL WHY ITS HEAT-UP?(CABLE LENGTH IS 15 METERS ONLY)

Answer

If motor is connected in Y/D connection, then the cable size
is used OK, Check the both motor & panel side terminal
connection is loose . After this if you found cable heating
then check the voltage,current& POWER FACTOR. If necessary
put 25KVAR Capacitor Bank at motor side.

Question { 6683 }

what is the power factor of an inductive load ?
(i) Zero (ii) Lagging (iii) Leading (iv) Unity

Answer

Your question is know about the power factor of an inductive
load, thus only one answer is LAGGING.The other factors are
also given to you to understand
1.inductive ---lagging
2.capacitive ---leading
3.resistive ---unity(perfect unity not practically possible)
4.zero--- worst case scenario lots of trouble

Question { 6777 }

WHAT IS THE FUNCTION OF PULSE TRANSFORMER IN DC DRIVE

Answer

pulse transformer is used to fire the thyristor gate-cathode
as per required.Anode is supplied with voltage & firing will
be done to thyristor as per referrence voltage

Question { 4080 }

Why only plate(copper) Earth pit given for neutral earthing? why not pipe(G.I) Earth pit?

Answer

The resistivity of Earth is 100 ohm-m compare this with
resistivity of copper which is 1.7 x 10-8 ohm-.m (
0.017ohm-mm2-m) & that of GI is 1 x 10-7 (0.1ohm
-mm/m),definitely neutral earth is more resistive than
copper or GI.eVEN INDIAN STANDARD recognasises this fact.It
mention in the clause 0.3 that the "the earth now rarely
serves as part of the return circuit, but is being used
mainly for fixing the voltage of the system neutrals"