Question { Bhel, 32108 }

HOW TO FIND OUT 1. LINE CURRENT, 2. PHASE CURRENT IN AN
ALTERNATOR / TRANSFORMER WHICH IS FEEDING A I)STAR LOAD ii)
DELTA LOAD, USING A CLAMP METER.

NORMALLY WHEN WE USE CLAMP METER IN A DG SET THEN WHAT DO
WE GET?? PHASE CURRENT OR LINE CURRENT.

Answer

line current means the current flowing through the AC
supply lines.phase current means current flowing through
each phases like R or Y or B phases.relation between line &
phae currents are

star connected system: phase current =linecurrent
delta connected system: phase current ={ linecurrent/√3}

for balanced 3Ф 4W system current flowing through the
neutral will be sum of phase currentsand will equal to zero.
ie Ir+Iy+Ib =0 =In

Question { Power Grid, 32420 }

What is GIS Substation and how it operate? where these type
of substation installed?

Answer

GIS means gas insulated substations.
SF6 Gas Insulated Substations (GIS) are preferred for
voltage ratings
of 72.5 kV, 145 kV, 300 kV and 420 kV and above. In such a
substation,
the various equipments like Circuit Breakers, Bus-Bars.
Isolators,
Load Break Switches, Current Transformers, Voltage
Transformers
Earthing Switches, etc. are housed in metal enclosed
modules filled with SF6 gas.

The SF6 gas provides the phase to ground insulation. As the
dielectric strength
of SF6 gas provides the phase to ground insulation. As the
dielectric strength
of SF6 gas is higher than air, the clearances required are
smaller. Hence,
the overall size of each equipment and the complete
substation is reduced
to about 10 % of conventional Air-insulated substations.

As a rule GIS are installed indoor. However outdoor GIS
have also been installed earlier

Question { 19310 }

what happens when d cexcitation given to alternator is
removed while it is running or what happens when dc
excitation is failed in alternator while running?

Answer

if excitation failed , the alternator will stop making
voltage.because when exciter fails, the main winding will
not produce rotating magnetic field, so voltage will not
produce.

Question { Cipla, 121857 }

1 tr is equal to how many Kw .is there any specific formula
for this to get the result .

Answer

one ton refrigeration ton(TR)was defined as the heat
absorved by the one ton of ice (2000 pounds) causing it to
melt completely by the end of one day ( 24 hours).

1 RT= 2000 POUNDSX 144 BTU per pound / 24 hours
= 12000 BTU'S per hour
= 200 BTU/min
= 3.517 kj/s
= 3.517 kw
= 3516 watts
= 4.72 HP
so, TR= 3.517 KW

Question { L&T, 10608 }

If load is 240 kw & pf is 0.8 lagging, than how to increase
it from0.8 to 1.0(unit),which rating capacitor used, please
give me Calculation. What is effact of consumer & suplier
if pf is lagging or leading with on effect machines/ TF/GE
etc.

Answer

required kvar= 240 kw x 0.750= 180 kvar
0.750 is the multipling factor.
you have to use 180 kvar capacitor.

Question { 10556 }

what is the disadvantage if earth is connected to neutral

Answer

we connect earth in all the machines to save machine and
man by electric shock. because the leakage current passes
to the earth by earthing wire.if we connect the earth wire
to neutral:- the leakage current will flow in the same
circuit and increase unbalancing.it is very dangerious for
man and machine.

Question { NHPC, 68560 }

What is AVR? Explain the function AVR?

Answer

AVR-means automatic voltage regulator
AVR regulates the voltage of a generator. when voltage
drops, due to load increase, AVR gives voltage to exciter
and exciter more xecites the alternator and voltage improve.

Question { 15067 }

if AVR fails in D.G set, what will be the effect?

Answer

suppose one 11KV DG is running, when we start the DG it
will make only 600 to 700v only, because that time the AVR
is not connected in the circuit, when we switch on the
AVR , the AVR gives the supply to exciter assyembly and the
rotor of alternator gets more exciting current and this
rotor current cuts more flux and the main voltage
increases , when it reaches to 11000v , the AVR sense the
11 kv and it minimised the supply voltage to exciter.
so we can say that when AVR fails, the generator will not
make voltage .

Question { 7388 }

What is power focter ?

Answer

Mr.bijay you are good explainer.
please share this knowledge to every-body.

Question { 18833 }

On load tap changer (OLTC) explode?
Transformer
Vector group: Ynd11
Rated Power: 353MVA
Rated Current: 693A
Voltage:294/20KV

OLTC
Type: T III Y1000 110/c 12193w
Max Operation Current: 295A
Step Voltage: 550V
Arrangement in Tx windings: Y Connection

Problem: Damage of Unit 1 Generator Transformer On Load Tap
Changer (OLTC)

Description of Incident:
9.00 a.m. :- Generator No Load test on excitation system
started

10.30 a.m :- Carried out AVR change over
test

11.30 a.m :- Preparation for Generator Manual Synchronizing
test


12.00 a.m :- Manual Synshronizing test started.
Observed incoming generator voltage higher than running voltage.
CECR operator operated Generator Transformer OLTC to bring down
the incoming generator voltage

12.03 a.m :-Generator Transformer abnormal alarm operated at
Gen.Control Desk (CECR)
CECR operater at Generator transformer bay informed that the
transformer
oil splashed out from OLTC.
CECR operater informed that he heard explosion inside OLTC.
Observed Oil level & Oil Flow alaram operated at Tranformer
local annunciator.

12.05 am :- CECR operator 'Open Gen Field Breaker”

12.10 a.m. :- Elec1 team inspected the OLTC and found the
OLTC rupture disk was broken
and oil spilled at OLTC area.
- Elec1 found the OLTC top cover bulging.

Do anyone know why and possibility cause happen in this OLTC.

Answer

please check the OLTC inside
connections ,carefully .because some times the connector
plate rollers not touch properly. so the winding temp.
increases continuously and oil will over-heated.

Question { Hyundai, 28427 }

what is the difference between KVAR & KVA ?

Answer

KVA=KW/COS.theta
kvar= kw/ sin.theta

Question { IIT, 4902 }

wat is syncronization . wat parameter will take for
syncronization.

Answer

when one Generator is running and suppose its rating is
1500 kva/1200 kw,and load increased and we wants to put
more load on GENERATOR . So then we have to run second
generator and to be shift some load on second generator,
otherwise the generator will be over loaded and tripped on
over-load fault. when we connect two generators parrallel,
this arrangement is called synchronisation.we connect the
out-put supply of both generators parallel by
synchronisation.In synchronisation we have to match these
parameters--phase sequence, frequency and voltage.when all
three parameters match we ON the breaker and
synchronisation complete and now we can put more load
(about 2000 kw) on generator.

Question { 5435 }

We have 2 no. 4MW DG set. and GEB supply.
But, we running, only 1 DG set. when we done APFC/Power
factor setting : 0.90, then winding temp. Low. but when
setting done : 0.83, then Winding temp. increase.
WHY Why ? ? ?, plz give me answer.

Answer

i think the main reason is load. when the power factor is
0.90 then the generator run smoothly and not over loaded.

Question { 4877 }

Can we connect more than one NGR at a time of different
rating of generators. what is advantage or disadvantage.

Answer

If we connect two NGR at a time , there is a possibility of
producing circulating current. and the generator will tripp
on circulating current fault. so normally we disconnect the
neutral of first generator and then we connect the other
generator neutral with NGR.

Question { BARC, 8771 }

what is the differance between MC61C and MC61A relay of L
&T make.

Answer

MC6161C and MC61A andMC31A are over load current protection
relays . all are different range relays and settings.