Question { 2782 }

why lightining is not available in swith yards?

Answer

mANGAGEMENT DECISION-SECURITY OR ENERGY SAVING,
GENERALLY ,IT IS DESIGNED FOR NORMAL AND EMERGENCY SOURCE
LIGHTING

Question { Areva, 8475 }

How to test and satisfy the conditions of the vector group
YNd1 for power transformer?

Answer

THIS IS ONE OF THE MANUFACTURER TEST OF VECTOR GROUP.
IN THIS TEST , THE HV RPh or Uph is connected to low voltage
rPh. /uPh. then 400v 3ph is applied. various voltage are
measured. (RS,ST,TR, R-N,S-N.T-N, r-s,s-t,t-r, r-N,s-n,t-n.

then, draw the graph,
refer to electrical hand book-transformer, any text book
also,manufacturer test report

Question { 2515 }

what are the causes for strip heater failure ?

Answer

INSULATION FAILURE, LIQUID/WATER BEING EMPTY OVER
TEMPERATURE

Question { 4240 }

what is meant by PU value ? anyone can you explain briefly to
me ?

Answer

PU means PER UNIT VALUE.
this is used by protection engineers application.
refer CEGB, ABB,SIEMENS HAND BOOK FOR CALCULATION OF FAULT
CURRENT.

Question { 3495 }

need help,
please can someone tell me how can i calculate the main
breaker and branches breakers to distribution panels (MDB)
depending on the load ampere .. i really need it but can't
find any site >>

Answer

refer to siemens ,Abb, schnieder ACB,MCCB,MCB
MANUFACTURER CATALOGS.

Question { MSEB, 14635 }

What is maximum permissible length of cable from transformer
(33kV/0.433kV) HT side to HT panel which contain VCB? In
which standard i shall get this information.

Answer

this is a practical problem.
Generally , Station auxiliary or Unit auxiliary
transformers are located very near to load consummer PCC/mcc
building.
High voltage current is less and Low voltage current is
very high,say 1250kva-33/0.42kv,21/1800A,
5MVA,33/0.42KV,87A/7210A. therefore, the distance between
33kv MV SW.GR FEEDER to your transformer location could be
500-1000m as per voltage drop calculation.we have the
system around this distance.
the advatage is LOw voltage from power transformer to PCC
SW.GR IS BUS DUCT. Huge low voltage power cable are totally
eliminated. Maintenanve free. electrical engineering hand
book.siemens ,abb

Question { TATA, 6975 }

Which motor has more efficiency ;Synchoronous or Induction
motor ?

Answer

synchronous motor. Induction motor is commercial motor with
less efficiency

Question { 2992 }

What happens when the power factor is leading and its
disadvantages.

Answer

THIS IS CASE USEFUL FOR UTILITY GRID MANAGEMENT.
GENERALLY EACH POWER GENERATION EQUIPMENT IS MANUFACTURED
WITH say 162MW is designed to operate on 80MVAR 0.8PF
LEADING and 30MVAR 0.8-0.9PF lEADING. THIS IS THE PROPERTY
OF gENERATOR CHARACTERISTICS.
wHEN GENERATOR IS CONNECTED (SYNCHRONIZED), WITH GRID,
THEN ,GRID DETECTS THE lOAD. AS DEMAND INCREASES THE POWER
FACTOR CHANGES FOR LAGGING TO lEADING. THE MVAR EFFECT IS
MORE IN PEAK LOADS,BASE ,..
THE EFFECT OF POWER FACTOR ON GENERATOR IS THE ROOTOR GETS
HEATED DUE TO REACTION OF ELECTROMAGNETIC FLUX DEVELOPED
BETWEEN STATOR AND ROTORS FIELD.
the stability of the grid is to be increased by MVAR
compensator or capacitor banks according grid compensation.
as Utility is another organization ,they take advantages of
capacity of genarator.as a result , generator is subjected
overheating, if operated still, the generator is pulled out
of synchronism and trips.disadvantage is shoter life due to
rotor heating and expensive repair,prolonged unscheduled
outage,revenue loss.

Question { Reliance, 18061 }

What is the basic difference between 90% stator earth fault
and 100% stator earth fault, and its phenmenona?

Answer

This is an application with power plant genrator protection.
In early 1950-75,only 90% stator earth fault protection
used for Generator Stator winding.
GE,westinghouse,hitahachi,GEC,BBC,KWU.ON 1975 ONWARDS,
THEN 100% STATOR EARTH FAULT DEVELOPED USING OPEN DELTA
VOLTAGE OFGENERATOR AND USING FIRST AND THIRD HARMONIC
BRIDGE.
WEST AND EUROPE,INDIA USED GENERATOR NETRAL GROUNDING
TRANSFORMER AND ON SECONDARY OF THIS TRANSFORMER90%STATOR
EARTH FAULT PROTECTION IS USED.
FOR 100% STATOR EARTF FAULT USE OPEN DELTA VOLTAGE.
Russian practice is use voltage transformer for generator
neutral gounding.
when I was DISCUSSING this with european manufacturer, they
want to delete 100% protection.In a generator it is meaning
less.fault is fault.It is time consuming for repair.
As a new challenge-generator manufacture claim 100%
availabilty of Generator with VIP.
/MICADOUR ELASTIC INSULATION. In gas turbine a single
generator rating is selected for single shaft gas turbine
and steam turbine. upto 275MW. AND 400MW

Question { ABB, 23389 }

purpose of breaker contact multiplication relay?

Answer

Generally manufacturer provide only 2NO+2NC Contacts.But
the client need more application such as remote
indications,interlocks,other switching operations photocell
camera,DCS,.....which need more contacts to represent CB
conditions. this is done with multiplication relay.

Question { Engro, 5221 }

What will be done if we open the secondary of CT on load??

Answer

there is heavy voltage developed according to turns ratioof
CT.and throws out the person -touch voltage is high/step
voltage is also high.some times he can not be isolated, the
person who touches him also can be electricuted.

Question { Engro, 5221 }

What will be done if we open the secondary of CT on load??

Answer

there is heavy voltage developed according to turns ratioof
CT.and throws out the person -touch voltage is high/step
voltage is also high.some times he can not be isolated, the
person who touches him also can be electricuted.

Question { 3598 }

Hi.I want to ask how to calculate contactor rating current?
for example I have 460 V , 100 A (induction motor)
calculate contactor rating current?

Answer

generally, 150 % of current rating of contactor or
contactor selection guide.

Question { 3598 }

Hi.I want to ask how to calculate contactor rating current?
for example I have 460 V , 100 A (induction motor)
calculate contactor rating current?

Answer

generally 1.5xIn,as for manufacturer selection guide table.

Question { 4699 }

I want to know what must the CT ratio be on a load of 300A
is a 3PH nutral to earh installation?

Answer

The neutral is a point in power transformer or in motor
connection where all phases are connected.In this point
voltage is zero. when you connect thisoint to earth, the
fault current or capacitance circulating current flows to
earth.
when a fault occurs , current is high.Therefore,CT ratio
should be 1000-1200/5 or 1A.

It is usually upto designer or protection device supplier.