5 MVA Generator

[magneticted]

Customer has a 5MVA Generator operating in island mode, and the question is what would be the biggest motor we could connect to this GEN considering a typical IEC 6Kv motor with starting current ratio of 6.5 times flc.Efficiency 95% and power factor 0.90, and a starting voltage of 80%

 

[asekhar]

The maximum rated motor that the generator can start will depend on many factors.

What is the base load?
What is the generator AVR droop characteristic?
Since you mention 650% starting current, I assume that you are only considering DOL start, if you use other means of starting, you will be able to start higher rated motors also.




Anand Sekhar

 

[petronila]

Hi Magnetited,

The faq237-766 Could help.

Regards

Petronila

 

[waross]

(5MVA minus base load)/3
respectfully

 

[petronila]

Hello Magneticted,

This formula could help: Motor HP x(KVA/HP) x (1000/Motor voltage)= LRA.

Taking account the Generator most be cappable to deliver all LRA Then the Gen Amps = LRA.

LRA= 5000 KVA /1.73 x (0.8 x 6) KV = 601 Amps. Is/Im = 6.5 then Im = 601/6.5 = 92 Amps where Is = Istarting= LRA and
Im= I motor.

Motor KW = 1.73 x Vm x Im x PF x Eff = 871 KW

If you have a generator capable to whistand a instantaneus over load of 300 % then the new Gen KVA= 15000 and the new LRA = 1803 the new Im = 277 Amps and the new Motor KW = 2465.

You most take account the Gen Set characteristics in order to know if is possible a 300% overload and it`s lasting time.

Regards

Petronila

 

[LionelHutz]

Possibly up to around 5000hp depending on the starting method.

From what I've seen, most generators can support around 200% current for something like 10 seconds. So, for a full voltage start, Waross pretty much has it. Generator MVA x 2 / 6 or generator MVA divided by 3 meaning the motor could be about 1600kW. For reduced voltage start you can start a motor up to around MVA / 2 so the motor could be around 2500kW.

With a VFD you could get maybe get up to around a 4000kW motor or so. You have to take the efficiency of the motor and the VFD off the generator capacity. The motor and VFD together might be around 80% to 85% efficient.

Of course, this is all theoretical and it really depends on the complete system so it needs to be studied in detail.

 

[itsmoked]

And the base load. And how much dip your motor starter can tolerate before chattering the whole thing into oblivion.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com