Short Circuit Current of Standby Generator

[mbrooke]

How do I determine short circuit current (L-G and L-L-L) of standby generator set, in the 125-750kw range? How long can a set handle or export this current? What happens when it goes beyond 10 seconds? Does the current differ the first few cycles vs the rest of the duration? What happens to the output voltage when a generator is shorted? Does the short circuit power factor change any dynamic?


In so far I'm getting 7.5 times the rated current for a bolted L-G fault not to exceed 5 seconds and 3 times the rated current for a bolted L-L-L fault not to exceed 15 seconds before stator exceed 300*C.

I want to make sure down stream circuit breakers clear before the gen set stalls out or becomes damaged.

 

[Dsg319]

Generators available short circuit current

I have been looking through manufacturers literature and found very little info as to the available short circuit produced by the generator. Only thing I have been able to find is 250-300% of rated current (for 3 phase fault) and 700-800% of rated current (for 1 phase faults) depending on...

forums.mikeholt.com

Not sure if this helps any... getting ready to leave to head out to lake, so didn’t have time to read through it all.

 

[romex jockey]

How do I determine short circuit current (L-G and L-L-L) of standby generator set, in the 125-750kw range? How long can a set handle or export this current? What happens when it goes beyond 10 seconds? Does the current differ the first few cycles vs the rest of the duration? What happens to the output voltage when a generator is shorted? Does the short circuit power factor change any dynamic?


In so far I'm getting 7.5 times the rated current for a bolted L-G fault not to exceed 5 seconds and 3 times the rated current for a bolted L-L-L fault not to exceed 15 seconds before stator exceed 300*C.

I want to make sure down stream circuit breakers clear before the gen set stalls out or becomes damaged.

good Q's MBrooke, not that i can add any clarity to them, but consider a genny basically windings, a motor.
now <if> we were addressing motors, we'd immediately be referring to 430.32 , overload protection......

~RJ~

 

[mbrooke]

good Q's MBrooke, not that i can add any clarity to them, but consider a genny basically windings, a motor.
now <if> we were addressing motors, we'd immediately be referring to 430.32 , overload protection......

~RJ~

Well, I did find this. It seems the winding can overheat in a fairly short amount of time:

 

[petersonra]

Hopefully the generator protection relay would have tripped long before you get any actual damage.

 

[ron]

The subtransient reactance and decrement curves are what to ask for.

Here is a good article

https://www.stamford-avk.com/sites/stamfordavk/files/AGN005_D.pdf

 

[mbrooke]

Hopefully the generator protection relay would have tripped long before you get any actual damage.

What protects the genny? Its breaker or the electronic control system?

 

[petersonra]

What protects the genny? Its breaker or the electronic control system?

usually it is more than just a breaker.

 

[mbrooke]

usually it is more than just a breaker.

Can you explain further?

 

[petersonra]

Can you explain further?

There are specialty relays that are often used with generators to detect all kinds of fault conditions other than shorts and overloads.