Induction generator protection

[obut4]

What are the electrical protections necessary for a 900 KVA induction generator connected to a steam turbine?

Is an asynchronous motor protection relay enough or is a synchronous generator protection relay necessary?
The loss of excitation protection 40Z is for sure not necessary.

In case of short circuit on the line, the induction motor current will drop very quickly.
How should the overcurrent protection 50/51 be set?
If an instantaneous overcurrent protection is used, it may trip due to the inrush current when the generator is connected to the grid.
Is a voltage restraint or voltage controlled overcurrent protection 51V necessary?
Is a 49 thermal overload protection necessary?

51G and 64G Stator earth fault protections as used on synchronous generator will not work until the induction generator is connected to the network? is it correct?
What solution can be proposed?


Thanks for you help!

 

[cranky108]

The last small generator I set protection on was about that size. And frankly the protection depends on how much you are willing to risk, or not risk.

A differential, directional over current, and a non-directional over current, a syncro-check, under and over voltage. What ever else depends on your risk level.

Or because relays are inexpencive enough, buy a full package in one box, and turn off what you don't need, or have enough information to set.

 

[DRWeig]

All I was required to do on my last induction generator job (1000 KVA at 480 VAC) was the same protection I would have given it as a motor (overcurrent, short circuit, ground fault), plus reverse-power relay and remote stop relay for control by the connected utililty.

We used a speed control loop to bring it up with the turbine and get it as close as we could to synchronous (no-load) speed, then closed the breaker and turned the turbine over to backpressure control.



Good on ya,

Goober Dave

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[obut4]

Thanks for your answers!

 

[GearlessGenerator]

FYI:

In case you want operate an induction generator at low speed (18->300RPM)without gearbox, these diode circuits will be very much helpful.

http://www.philica.com/display_article.php?article_id=316