Answer / ravi - cement plant india

Transformer and genrator PF depends on the nature of
connected load ( Motor ), But motor has its own fixed Power
factor

Therefore Transformer and genrator capacity shown in KVA (
Without PF ) and motor Capacity shows in Kw ( with power
factor )

Answer / balaji

Generator is producer of Voltage and Current, we can
connect load as such draining full load current or half
load, even noload,but voltage remain moreover same.So it
willl rated in terms of product of V*I, secondly it gives a
electrical output for any Load(may Capacitor,Inductor &
resistor),so it is consider as Procuct of Voltage & Current
excluding powerfactor.
Whereas motor is machines coverts electrical Energy to
Mechanical energy, so it is rated in KW

Answer / zulfiquar wani

Generator and transformer are rated in KVA becoz at that
time we dont know the consumer power factor as we know that
the (KW= KVA X Cos Phi) as we know the power factor we have
ratings in KW and on the other hand motor has defined power
factor and the rating has been mentioned in KW for example
if we have transformer of rating 50KVA this rating of
transformer is its apparent power that is KVA if we
multiply the same withh the power factor 0.85 we will get
the real power that is KW

KW= KVA X Cos phi
KW = 50 X 0.85
KW= 42.5KW

Answer / p tiwari

Generator is a source of power. It includes active as well
as reactive power. It deliver only active power while
working on unity power factor. It deliver reactive power
only while connected to a purely reactive load. It can
deliver both of these powers while connected to a composite
load. This signifies that the current limit is the main
factor here. You can draw a purely rective current of rated
value or purly active current of rate value. combination of
output depends upon the load but the maximum limit is
prescibed.
When you are drawing both of the currencts active and
reactive, in such condition how much the alternator can
deliver? it can be descibed by KVA only not by KW. That is
why alternators are rated in KVA.
Motors are rated in KW only because for motors the load is
mechanical and thus only active power which is converted to
mech. is significant.The power factor of the motor is
independent of the load and at whatever powerfactor it
works it is due to its desing.

Answer / sdvyas

Generator rating is given in kVA,as generator is the souce
and delivers power to load. Load may be resistive,inductive
or capacitive.A 10 MVA generator will deliver 10 MW load if
power factor is unity,however if the power factor of the
load is 0.8 then generator can deliver active power up to
8MW only.It is up to user who efficienly generator power
may be utilised. Therfore, manufacturer always specify the
generator rating in KVA or MVA.

On the other hand, motor converts electrical energy into
mechanical energy.Therfore,its rating is given in KW as
power factor of the motor remain constant.

Answer / yajnesh

The rating of generator is described in terms of KVA by its
manufacturer because the generator will produce a constant
voltage on which it is designed and the current will depend
on the nature of load,for same load it delivers more
current for poor power factor and less current for unity
power factor, since the manufaturer does not know the
nature of load he desribed its rating in terms of voltage
and current.

While in case of motor, motor have fixed power factor.

Answer / iftikhar ahmed

Any device is rated depending on losses of the machine. In
a transformer the losses are iron losses which depend on
voltage and copper losses which depend on current so there
are no losses which depend on power factor hence
transformer is rated in KVA.the same thing applies for
generator aswell.

Answer / r.baskar

We all know that the factor "Power factor" comes only when
the voltage & current waves are travelling at a time
difference. This will happen due to the
inductive /capacitive nature of the load(Depends how the
load receives the power from the sourcei.e whether voltage
first (inductive)or current first(capacitive).

But at the time of producing the power, voltage and current
waveforms are starting from the source at the same time
only. Hence the question of power factor does not arise...

Hence DG is rated in kVA only...

Pls clarify ...

Answer / shiv mishra

We know that
KW=KVA*PF
Therefore according to this eq if pf is known then the rating will be in KW either rating will be in KVA.
In the generator pf is depend on the load because it convert mechanical to electrical energy.but in motor electrical convert into mechanical energy in which pf is constant.
Therefore generator rating in KVA & motor rating in KW.

Answer / mohan

generators and trasformers are rated i kva.kw=kvaxcos
(phi).the manufacture didn't no custmor load(in kw).one
more answer iron losses depends on supply voltage and cu
losses on current.so taht kvxi=kva

respetsed sir, i have applied for section engg and juniour engg for both chennai and tiruvunabthapur boards for electrical deportments . can u suggest what books i have to follow and and also from which sections they r going ask (i mean weightage and what topics i have to cover) for both se and je for both chennai and tiruvunanthapur boards.......

1 Answers  

RELAY 1. REF RELAY : • OPERATION WITH CT CURRENT FLOW DIRECTION. • WHY REF RELAY WHEN DIFFERENTIAL RELAY IS THERE. • REF RELAY STABILITY CHECK BY PRIMARY INJECTION – WHICH POINT FOR CUR RENT INJECTION. • WHY REF RELAY NEED STABILISING RESISTOR. IF RESISTOR SHORTED OR BYPASSED, WHAT WILL HAPPEN. • WHICH TYPE OF RELAY FOR REF, HIGH IMPEDANCE OR LOW IMPEDANCE. • IF NEUTRAL CT IS NOT CONNECTED IN THE CIRCUIT, WHAT WILL HAPPEN. • REF PROTECTION ACTS ON WHICH OF FOLLOWING: SINGLE PH. TO E/F; PH-PH TO E/F; THREE PH. TO E/F. 2. DISTANCE RELAY : • BASIC PRINCIPLE AND TYPES • SWITCHED MODE PROTECTION – WHY IS IT CALLED SO. • SCHEMES USED • WHY ZONE-1 SET AT 80% • SETTING RANGE FOR ZONE-2 AND ZONE-3 • HOW SINGLE PHASE TO GROUND FAULT MEASUREMENT IS DONE. • 3. WHAT IS POLARITY. CT LOCATION IF INTERCHANGED WHAT WILL HAPPEN. 4. SOLKOR RELAY: 1. WHY SOLKOR IS USED. 2. CIRCUIT DIAGRAM OF SOLKOR RELAY 3. DIFFERENT PARTS OF RELAY 4. HOW IT WORKS. 5. EXPLAIN BY VECTOR DIGRAM. 6. WHAT ADVANTAGE FOR USING SUMMATION TR. 7. DIFFERENCE BETWEEN R & RF WITH CIRCUIT. 8. ADJUSTMENT OF PADDING RESISTANCE. 9. WHAT IS LEAKAGE CURRENT AND HOW TO MEASURE. 10. WHAT HAPPEN IF LINK IS LEFT OPEN. 11. 5KV/15KV INSULATION TR. ARE USED IN WHICH SYSTEM. 12. WHAT PRECAUTION TAKEN DURING TESTING. Relay Page 1 of 5 13. PROCEDURE BEFORE TESTING AND AFTER NORMALISATION. 14. HOW RELAY IS TESTED IN LIVE CONDITION. 15. RANGE OF SPILL CURRENT ANS SETTING OF RELAY 16. IF MEASURED CURRENT IS 5MILLI AMPS, CAN RELAY OPERATE. 17. EACH FAULT APPROXIMATE VALUE OF PICK UP. 18. WHAT IS THE REASON SOLKOR-R MODE PILOT SHORTED CONDITION RELAY CURRENT PRESENT. 19. AFTER SHUTDOWN, WHY NEED TO OPEN SOLKOR PILOT, IF NOT WHAT WILL HAPPEN. 20. AFTER NORMALISING WHAT CURRENT TO BE MEASURED, WHAT IS ACCEPTABLE LIMIT. 21. WHAT HAPPENS IF PILOT OPENS FROM RELAY, WHEN FEEDER IS LOADED. 22. CAN WE USE THIS RELAY AS O/C OR E/F RELAY. 23. ANY RELAY OTHER THAN PILOT CABLE TYPE. 24. IF FEEDER TRIPS ON SOLKOR, WHAT TO DO. 25. WHAT HAPPENS IF PILOT POLARITY REVERSE. 26. WHAT HAPPENS WHEN CT SHORTED AT ONE END. 27. WHAT HAPPENS IF PILOT SHORTED – STATUS OF RELAY 28. WHAT HAPPENS TO RELAY ,IF POWER CABLE GETS OPEN. 29. WHAT HAPPEN IF PADDING RESISTOR IS SHORTED AT ONE END. 5. TR. DIFFERENTIAL: 1. CIRCUIT DIAGRAM 2. DIRECTION OF FAULT CURRENT. 3. WHEN THE FAULT IS IN ZONE AND OUT OF ZONE. 4. CT CONNECTION IN PY. AND SY. SIDE. 5. BIAS SETTING AND BIAS CURRENT. 6. WHICH BIAS SETTING USED IN TRS. FOR HIGHER TAPS. 7. PURPOSE OF RESTRAINING BIAS COIL. 8. WHY BIASING REQUIRED. 9. EXPLAIN IPCT, FOR EXAMPLE, DYN10 VECTOR GROUP. WHY MATCHING TR. USED. 10. WHY NEED 2ND HARMONIC BLOCKING DURING INRUSH. 11. WHICH HARMONIC IS MORE 2ND OR 3RD. 12. HOW TO AVOID FALSE TRIPPING IN DIFF. PROTECTION WHEN INRUSH CURRENT FLOW DURING TR. IS ENERGISED. Relay Page2 of5 6. DIRECTIONAL RELAY: 1. CIRCUIT FOR USE OF DIRECTIONAL PROTECTION SYSTEM. 2. WORKING ZONE / NON-WORKING ZONE. 3. HOW THE CORRECT DIRECTION OF FLOW OF CURRENT IS DETERMINED. 4. CT & PT CONNECTION DIAGRAM. 5. SETTING OF PHASE & EARTH FAULT ANGLE AND OPERATING REGION. 6. WHICH DIRECTION IT IS PROTECTING. 7. WHAT PROTECTION AVAILABLE FOR POWER TR. 8. WHY CT CONNECTION IS STAR, IF TR. WINDING IS DELTA. 9. DIFFERENCE BETWEEN REF AND DIFF. RELAY 10. WHERE IS O/C & E/F RELAY CONNECTED EITHER HV SIDE OR LV SIDE AND HOW E/F RELAY WORKS IF TR. WINDING IS DELTA CONNECTED. 11. IN DELTA WINDING OF TR., IF ONE WINDING IS CUT AND NOT EARTHED, WHICH PROTECTION WILL ACT. 12. IF DIFF. & REF RELAY ARE NOT WORKING, WHAT IS BACK UP PROTECTION IN TR. 13. WHAT IS PURPOSE OF NGR AND HOW STANDBY E/F RELAY WORKING, TESTING PRECAUTIONS IF COMMON NGR IS USED. 14. WHAT IS PROTECTIVE ZONE OF STANDBY E/F RELAY. 15. WHAT ARE PROTECTION AVAILABLE FOR FEEDER. 16. AFTER TR. IS NORMALISED, WHAT CURRENT TO BE MEASURED. 17. BUSBAR PROTECTION: a. BASIC PRINCIPLE AND DIAGRAM WITH CURRENT DIRECTION. b. WHY OVER LAPPING CT’S REQUIRED, IF NOT WHAT WILL BE THE EFFECT. c. WHY CT SUPERVISION REQUIRED, HOW TRIPPING IS AVOIDED, WHAT IS CT SUPERVISION SETTING VALUE. d. HIGH IMPEDANCE & LOW IMPEDANCE TYPE e. TEST PROCEDURE(STEP BY STEP) f. AFTER NORMALISING, SPILL CURRENT VALUE AND LIMIT. Relay Page3of5 18. CIRCUIT BREAKER FAILURE – FUNCTION, WHY NEEDED, HOW TRIPPING ARRANGEMENT. 19. WHY INSTANTANEOUS ELEMENT IS NOT USED IN THE NETWORK. 20. WHEN FEEDER IS LIVE AND BY MISTAKE LINE EARTH SWITCH IS CLOSED, WHICH RELAY OPERATES – O/C OR E/F. 21. DURING TR. SWITCHING ON, IF DIFF. RELAY IS BLOCKED BY 2ND HARMONICS, WHAT ARE THE OTHER PROTECTION IN SERVICE. 22. WHICH OF FOLLOWING PROTECTION OPERATES FAST, WHEN 11KV CABLE COMPARTMENT GET FLASH OVER: CABLE DIFFERENTIAL; OVERCURRENT & EARTH FAULT; ARC PROTECTION. 23. WHICH PROTECTION OPERATES WHEN ANY ONE OF THE OHL PHASE IS CUT AND HANGING, NOT TOUCHED WITH EARTH. 24. WHAT ARE DIFFERENT TTB ALARMS – HOW YOU KNOW THERE IS ANY ALARM. 25. WHAT IS CIRCULATING CURRENT AND HOW IT WILL COME. 26. IF ONE TR. TRIPPED ON DIFF. RELAY WHAT YOU WILL DO. 27. IF SUB-STATION TRIP ON BUSBAR PROTECTION, HOW YOU WILL RESTORE. 28. WHAT IS CT SATURATION. HOW IT IS CARRIED OUT. 29. D.C EARTH FAULT – HOW YOU WILL FIND OUT. Relay Page 4 of5 30. PILOT WIRE SUPERVISION – HOW IT WORKS 31. IN 11KV SWITCHGEAR DBB SCHEME, ONE E/F RELAY IS FAULTY IN ONE FEEDER AND THERE IS NO SPARE FEEDER – HOW YOU WILL NORMALISE THE FEEDER. 32. WHICH PROTECTION IS USED FOR LONG CABLE FEEDER 33. DIFFERENCE BETWEEN TRAFO. DIFF. AND CABLE DIFF. PROTECTION. 34. WHAT TYPE CHARACTERISTIC AVAILABLE FOR O/C AND E/F RELAY. 35. WHAT IS THE DIFFERENCE BETWEEN STATIC AND ELECTRO- MECHANICAL O/C RELAYS. 36. WHAT IS DEAD ZONE 37. HOW TRIPPING OF OTHER ZONE AVOIDED WHEN BUS SECTION CB IN OPEN CONDITION FOR DEAD ZONE FAULT. 38. IF OUT OF STEP ALARM COMES WHILE ALL TR. IN SAME TAP POSITION, WHAT YOU WILL DO. 39. WHAT YOU WILL DO IF AN 11KV FEEDER FAILED TO TRIP ON: O/C or E/F or SOLKOR. HOW YOU RESTORE THE SUPPLY. Relay Page 5 of5

2 Answers   KSEB, Siemens,

how to calculate cable size by amp

19 Answers   CDS,

please give me solution to rectify the emi(electromagnetic interference)

0 Answers   Powergear,

Why 11KV PT Secondaries [(11000/1.732)/(110/1.732)/ (110 / 3)]are in star connection ? And why the same should not be in delta ?

1 Answers  

I have 4 DG set with 1500KVA rating. system breakers are 11KV & alternator are 415 Volts. Between alternator & breaker one stepup transformer used. i want to Know what is max. resistance for body earthing & 415 & 11KV V Neuteal earthing. my fault current is 14 times for 2 sec.

0 Answers   Jindal,

What are the classifications of heating element?

0 Answers   BARC,

The maximum demand of consumer is 2 kW and his daily energy consumption is 20 units. Its Load Factor is (1) 10.15% (2) 41.6 % (3) 50 % (4) 60%

2 Answers  

What is the lockout relay

0 Answers  

On 400 amp factory load how kvarh capacitors provide

0 Answers  

what irequirment need to be followed when working on live equipment

0 Answers  

Whether amorphous core transformer is available in India?.If available then up to what rating of voltage and KVA?.

0 Answers   DAE, Tata Chemicals,