Question { Phoenix Technologies, 4952 }

WHY AREWE USING THE 3 1/2 CORE CABLES IN POWER TRANSMISSION

Answer

If the load is fairly balanced ,the unbalanced current in
the neutral of 3ph 4w system will be very less and hence
the smaller sectional area for the neutral cable to save
money

Question { 16014 }

What is mean by earthed & unearthed cable? Voltage grade of
1.9/3.3 kV(E), 3.3/3.3 kV(UE), 3.8/6.6 kV(E)what it
indicates??

Answer

The metal sheath is earthed or unearthed. 1.9/3.3 and
3.8/6.6 are phase/ line voltages and are 3 core
cables.3.3/3.3 KV means 2 core cable for single phase
supply ,as neutral is present earthing is not necessary.UE
means unearthed E means earthed

Question { 4570 }

resitance in ac=1.6*resistance in dc

Answer

equal to or less than 1.6

Question { 37635 }

difference between EMVT, PT & CVT ?

Answer

EMVT-electromagnetic voltage transformer
PT-Potential transformer
CVT- coupling(capacitor) voltage tr

Question { 4507 }

Why tripping not occur when the transmission lines (11KV &
above) breaks? Doesn't
we provide earthfault protection for it?

Answer

All the tr lines should be provided with EF protection.11
and 33 KV lines are provided with 2 OC and 1 EF relays or 3
OCR and 1 EFR.The unbalanced current passes through the EFR
which is usually set at 20% of OCR setting.The EFR is
connected between star points of CT's and relays. For
higher voltages distance relays are provided with OCR and
EFR as back up protection.If the line breaks i.e.a
conductor opens out without touching earth .The distance
relay does not act as there is no heavy current.The EFR
will trip only if the unbalanced current exceeds the set
value .Hence there will not be any tripping if the line is
not loaded sufficiently. OCR=over current relay, EFR =earth
fault relay

Question { 6551 }

Why the ceiling fan rotate in anticlock wise direction
whereas tables fan rotates at clock wise direction?

Answer

It was introduced to India by Britishers to suck the smoke produced by fireplace from the bottom of the room . But they found that cooling was more important in India and changed the direction to blow the air downwards . Bi-directional ceiling fans are used where sucking is required during cold season and blowing during warm season.

Question { 8689 }

IF THE OUTPUT OF A 100KVA, 415V GENERATOR IS STEPPED UP TO
11KV WITH A 500KVA TRANSFORMER,CAN THE TRANSFORMER BE
LOADED ABOVE THE SOURCE GENERATOR RATING?

Answer

No. Tranformer is for only stepping up the voltage, not the
power which should not be allowed to rise above the
capacity of the generator

Question { 4038 }

Why PT burnts?

Answer

1) contamination of oil and insulation failure 2)lightning
stroke 3) over voltage4)over current and overheating

Question { 3156 }

diff between synchronous gen and alternators

Answer

nil, gen is also called alternator when the output is AC

Question { 3855 }

what is the internal fuction of a ceiling fan?

Answer

Ceiling fan has a single phase capacitor start and run
sqirrel cage motor.The consructoin differs from other
motors as it has the rotor (armature)outside the field
(stator),sorrounding it.The field is facing outwards.The
value of capacitor is 2-4 mic farads

Question { 5497 }

What is a soft start?

Answer

It is an electronic starter for large squirrel cage
motor,to limit the starting current, using microprocessor
and thyristors

Question { Manipal University, 5125 }

what is different between kvar & micro farad when its comes
across the capacitor rating
is it possible to convert kvar to mf or mf to kvar

Answer

1/Cw=XL V^2/XL=VAR

Question { 4438 }

when we see the lube oil grade its 15w/40 or 20w/40 in this
what is W Explain breifly

Answer

W -winter grade ( temp), 40 means SAE viscosity number

Question { 24477 }

What is the advantangeous over SFU (switch fuse Unit) & FsU
(Fuse Switch unit) which one is better & application of
Both?

Answer

SFU- switch -fuse-load.So it is easier to replace fuse.FSU-
fuse-switch-load-so it is easier to replace or repair
switch In case of wall sockets FSU is better and in case of
distrbution box SFU is better

Question { 5144 }

what is the working of loss of excitation relay (40G)? how it
is work?

Answer

LOE relay acts ,as its name indicates, when excitation fais
either due to field breaker(FB) opening or some other
cause.When there is no excitation the gen will run as synch-
motor or induction generator if the prime mover still
running. In both the cases current will be drawn from the
system ,hence power flow is reversed .Then the relay acts
to actuate the master trip.Earlier this relay acted only
when FB opened, closing a switch in the opened position .