Generator Short Circuit Test

[GQAES]

I have a MD-11 generator which requires a 5 second short circuit test. The generator is 120V, 3 phase at 400Hz and will be driven by a 200HP constant speed drive. The spec calls out for a circuit breaker to apply the short during which the generator is to put out 750A per phase for 5 seconds. I'm wondering what type of circuit breaker and what amperage I need to perform this test. Also, I'm wondering if there a way to toggle the breaker off and on other than manually, maybe remotely actuated. And finally, would I use a buss bar across the terminals of the breaker as the short? The spec says the total shorting impedance including the short circuit breaker shall not exceed 0.035 ohms per phase.
Thanks for any help.

 

[DTR2011]

Is this a one time test, or do you want a more permanent solution?

Google NEMA Circuit Breaker Combination Starters. Even for a one time test, you can likely find one on the used market. These are designed for remote open/close and are close in design to your intended application.

 

[rhatcher]

This sounds like a tough problem (at least for me). The selection of the breaker is relatively easy if your only criteria is to hold 750A for 5 seconds and to have electric close and open. Depending on trip unit type, you could probably get by with a 500 amp molded case breaker, maybe less if you do your research right. Your idea of bus bars to short the breaker terminals does sound like the best solution.

The problem is how do you control or limit the short circuit current to 750 amps. I'm guessing, based on the driving motor horsepower, that your generator is about 150kw. The short circuit output of the generator will be based on the voltage regulator, the type of excitation (self-excited, pmg excited, or separately excited), and the impedance of the 'fault' (short circuiting impedance). Depending on all of the above conditions, when you apply the short circuit you may get much more or much less than 750 amps.