Question { Reliance, 19495 }

Explen all type electrical protection ? like
O/C,E/F,NPS,VOLTAGE UN BLANCE,CURRENT UN BALANCE,NAGETIVE
PHASE SEQ,AND ETC...............electrical Protection

Answer

1) OC/EF/OC Relay :
CTs fixed on main 3 phases, these cts connected in star, OC
relays coils are connected by phase cts sec & EF relay
coil connected to star pt. of ct sec.When PH. current
increases OC relay trips as per settings.when any fault
occurs on phase, current flows through ct sec neutral & EF
RELAY TRIPS
2) SINGLE PHASE PREVENTER or PHASE DISCRIPENCY relay used
in voltage unballance
3) Under voltage relay trips by PT sec VOLTAGE set.
4) Thermal relay operates when current unballance between 3
phases.

Question { MacLellan, 54842 }

how to check the 3ph capacitor is good or not.

Answer

Actually any capacitor is 1 PH for 3 ph you have to connect
it in star.
For checking -
1) Isolate capacitor from cap. bank check it's capacitonce
by capacitonce meter.
2) Take IR value by megger
3) Given 1 ph supply to cap. unit as per kvar rating,
adjust supply voltage by dimmer if required.
4) Noted all this reading & check with previous ones.

Question { 8747 }

what type of protection and safety req. in the 220kv
substaion and area around the substation

Answer

Protection:-
1)Distance prot. relay
2)local breaker back up LBB relay
3)differential prot. relay
4)pole discripency relay
5)trip ckt supervision of sf6 gas relay
6)air pressure monitoring relay

Safety precautions:-
1)remove all vegetation inside yard
2)proper earhing to fencing & gate
3)proper watering & checking of earth pits
4)periodical cleaning of all C.T.,P.T.,etc insulators
5)while opening or closing off load isolators always wears
H.T. gloves
6)while closing isolator ensure that all 3 poles fixed
properly
7)monitoring the leakage current of lightening arrestors

Question { Hyundai, 37761 }

What is VCB? Where it is installed?

Answer

VCB means vaccum ckt breaker it can be used at any voltage
but due to its high cost it is generally used at HT side.
contacts of vcb operates in vaccum chamber.
It have spring charge moter,spring is used to operate
moving contacts.
It have closing & tripping coils & auxillery contact switch.
Can be operated manually also

Question { NCC, 111458 }

what is the function of anti-pumping in circuit breaker?

Answer

In ckt bkr closing coils are not designed for continous
operations, if you give constant commands this coil may
burnt. so to prevent this antipumping contactors used in CC
ckt.

Question { 12391 }

if only one generator is running in droop mode parrallel
with grid and suddenly grid breaker off what will happen?
It will trip o/u freq or stay as it is? (urgent)

Answer

Paralelling with grid mean your DG is running on stand by
mode or droop mode, your systems load is on grid. when grid
trips all load shifted on DG WITHOUT INTERRUPTION when grid
power comes check synchro. relay gives command again to DG
& it will again run on droop mode.

Question { 8244 }

why transformer neutrol is grounding

Answer

Generally H.T. side of trans.neutrol grounded through
resistor called NGR which is depends upon earth fault delay
time.At L.T. side neutrol grounded solidly .
This is because when earth fault occurs in phase, fault
current passes through neutral to earth immidiately to
avoide further damage to system.Earth fault protection
relay mounted on neutrel C.T.This relay operates properly.

Question { ME, 9677 }

At site, we have 30Kw motor (3 phase, 400V,50Hz) and FLC
54A as per the nameplate. At the time of starting it draws
840A instead of 390A (7.2%). As per the data sheet also its
390A starting current. it thru a dol starter from the MCC.
can anyone tell what is the problem in the motor

Answer

pl. check motors connection in terminal box if it is
connected in star then current may increased.