of generator cos phi
of generator cos phi
(OP)
hi, i wonder if we have plate cos phi value of 0,8 does it mean that a 1000 kVA generator will give nominally 800 kwatt? is there any drawback if we operate this generator with a load of 1000 kwatt? İf we could do it, so why do we have cos phi = 0,8 values on generators ups's etc...greetings..






RE: of generator cos phi
Looking at your prime mover (engine, turbine etc) again may not give any more power than 800kw
Use of 0.8pf seems to be historic, since it gives a margin above what is normally used. Any historians out there?
RE: of generator cos phi
Typically a 800kW prime mover will be coupled to a 1000kVA generator so that you can get the rated 800kW as long as your load power factor is better than 0.8. If you had a 1000kW machine connected to a 1000kVA generator you'd be very disappointed to find that you can only get your 1000kW at unity power factor.
RE: of generator cos phi
So does a 1000 KVA generator is capable of giving 900 or 950 or 1000 whatever (more than 800 kva) KVA out of its terminals electrically if this generator is rated 1000 KVA and cos phi = 0,8 on its plate?
RE: of generator cos phi
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla
RE: of generator cos phi
Do you want a prime mover/alternator combination that can supply the rated kW over a broad range of power factor or do you want a prime mover/alternator combination that can provide full alternator rated kVA at unity power factor? You can't economically have both, and the general preference is that the alternator be sized to provide full prime mover kW over a broad range of power factors.
RE: of generator cos phi
The current that a generator is capable of producing is determined by the heating effect of the current. If you draw more current than the generator is rated for it may burn up.
The voltage rating is generally the system voltage.
Multiply the volts times the amps and you get VA. Divide by 1000 for KVA.
That is the capability of the generator.
Loads tend to be at less than unity power factor. The prime mover is usually rated at less kW than the KVA. This generally gives good service.
0.8 or 80% is pretty standard for a PF rating on generators.
But, change the voltage and the KVA changes but the kW of the motor stays the same. Take a machine rated at 40 kW and 50 KVA at 240 volts and trim it down to 120/208 volts. The KVA is now based on 208 rather than 240 and drops to 43.3 KVA. The prime mover will still deliver 40 kW.
If the same generator is reconnected for single phase, the KVA drops to 33.3 KVA but the engine will still develop 40 kW. Care must be exercised so as to not overload the generator. It will have enough power to easily damage itself if not properly protected.
Bill
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"Why not the best?"
Jimmy Carter
RE: of generator cos phi
You have an 1000kVA and cosf = 0.8 (Pg=800kW, Qg=600kVAr), ofcourse, and you want to get more power than 800kW output energy because of your loads were over, I think. Is that correct?
If that, your generator will be heated as you know ('cause U R electrical engineer
1. For example, the load is 900kW and cosf=0.8 hence Q>600kVAr, you have to consider the rating of prime mover, if should, increase the prime mover speed. If not, you should increase the excitation current of the generator.
2. If the load has cosf <> 0.8, you should have manufacture's guide for reference.
RE: of generator cos phi
RE: of generator cos phi
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RE: of generator cos phi
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RE: of generator cos phi
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Eng-tips forums: The best place on the web for engineering discussions.
RE: of generator cos phi
RE: of generator cos phi
None of us can guess what your generator can deliver under all circumstances. You really have to consult specs for the diesel engine (for real kW) and the capability curve for the generator itself.
What you consider "theories" are plain facts that are valid also for your generator. But real limits are only found in the generator documentation.
The specific case with 800 kW output and 1000 kvar needs 800/efficiency kW from the diesel engine - as Pete and others have pointed out.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: of generator cos phi