Question { OPS, 7136 }

what is difference between start imitation and start
interlock for 3 phase motor protection ?

Answer

Start Limitation: It is the limitation from the Motor
Design side. There is a limitraion for motor from No.of
Consecutive hot Stat and Consecutive Cold Stat according to
motor themal withstandabulity.

Start Inerlock: It is permissiveness given to start the
motor from its protection or proceess interlocks.Example
motor cooling blowers should be on before motor starts.

Question { Grasim, 22507 }

Procedure for conduting vector group test on power
transformers.why it is conducted?

Answer

Purpose: The Polarity and Phase relation tests are
importent when two or more transformer are to be
paralleled.Parelleled transformer must have the same
polarity and phase relation to avoid parial or complete
short circuits.

Test Procedure:(Yyn11)
The L.V. vector will be superimposed on H.V. by connecting
1U & 2U Terminals. The three-phase voltage will be applied
to the line terminals of H.V. winding. Voltage measurement
will be done across:
1U-1V:
1V-1W:
1W-1U:

1V-2V: 1V-2W:
1W-2V: 1W-2W:
1U-2N: 1V-2N:



Checks: - 1V-2V = 1V-2W
1W-2V > 1W-2W
1U-2N + 1V-2N = 1U-1V

Question { Reliance, 14563 }

why do we generate only 3ph ac?is it possible to generate
4ph,5ph,....?

Answer

In Single Phase the Voltage or current will be Zero for
every Half Cycle

In Two Phase the Votage or current in one phase is zero and
at the same time other phase also zero and one phase get
peak and other also get peak becuase the phase diffrence is
180Dec. so here also no votage of current if one is zero.

In Three Phase the Phase diffrence between phases is 120Dec
so that if one phase is zero rest of two will get some
magnetude.So here we get Voltage or current if any one
phase is zero.

So there is no need to generate 4phase and 5phase systems

Question { Hindustan Copper Limited, 16821 }

how calculate gd2 of ht motors

Answer

Motor GD2 = (Load Gd2 x Motor RPM x Load RPM)/
(Motor RMP x Motor RPM)

Question { ABB, 23182 }

what is the difference between isolation and insolation ?
please explain in detail with example.

Answer

Isolation: It means saparation between equipment and main
supply.When we want to maintain a particular equipment it
should be isolate with mains supply.Other wise we can not
maintain it.

Insulation: It means an isulating material is provided on
the (live) cables or equipment according to their voltage
rating to avoid short ckt b/w live parts and earth faults
b/w live part and ground. This for our safety as well as
equpment safety.if it is not provided may cause so many
electrical hazards or limit the usage of cables in various
places.

Question { XLPE, 52186 }

what is meant by AYFY Cable?

Answer

AS Per IS:1554(Part1)&7098(Part1)

'A' - Alluminium
'2X' - XLPE Insulation
'F' - Steel Strip Armour
'y' - PVC Insulation
'W' - Steel Round Wire Armour
'y' - PVC Outer Sheeth
'ww' - Steel Double round wire armour
'yy' - Steel Double Strip Armour
'Wa' - Non Magnetic round wire armour
'Fa' - Non Magnetic flat strip armour

AYFY Means Alluminum PVC Insulated Fltat strip armour and
PVC outer sheeth cable

Question { 9525 }

Does frequency change with increasing voltage i.e 220v to
11kv? explain if not?

Answer

Frequency: No. of Cycles per Second (1/T). So Frequency
will depend on Time Period Not in Magnetude. If magnetude
of Voltage increases(220V to 11KV) threre is no effect on
Frequency