Short-circuit contribution of induction generators

[JLuc]

Hi all,

in the case of 1MW hydro powered induction generator, connected to the grid.

I know we should use subtransient reactance (13.3 to 16.7 %), for first cycle contribution, and 1.5xsub. transient reactance for interrupting time contribution (2 to 8 cycles).

My question is: is it correct to consider the contribution equal to 0 passed this point?

What will be the current after 10 or 15 cycles?

I looked in IEEE books and didn't find any infos about this.

Thanks for your answers/comments

JL

 

[cranky108]

I believe that in the US there is requirments for wind generation that requires a ride through factor of 2 seconds. But I am unsure it applies to new hydro plants, and it deffently does not apply to older hydro units.
However, depending on capacitor instalation, it is possible to have some self excitation, but the lower the voltage at the induction generator, the lower it will be.

If you find out something better than what i gave I would like to know, as I will be contending with a few hydro units soon.

 

[ijl]

I do not know about the IEEE-world, but the IEC 60909-standard gives equations and curves for the calculation of the symmetrical breaking current, including the contribution from asynchronous machines. The equations/curves are given up to 0.25s after the occurring of the short circuit. Thus, it seems that the contribution of asynchronous machines cannot be neglected after 10 cycles, but maybe after 15 cycles, according to IEC.

 

[QBplanner]

It depends on which type of fault level contribution you expected as well as your actual machine characteristics and transient performance.

You can not ask the question without considering realted factors unless high level answers are required

 

[JLuc]

The reason I'm asking this is for protection coordination purpose.

Let's say the generator has a 500A sub. transient contribution for a line-ground fault at the utiliy's substation. With a current of this magnitude the utility's ground fault protection takes, say 0.25 sec. to operate.

Then, in case of a fault on a adjacent line in the substation, I don't have to worry about the generator contribution to trip the hydroplant line breaker. The generator contribution will decay to 0 long before the relay trips.

JL