disconnector rating.

[Mlmlzx]

Dear Sirs,

Can somebody please tell me what current rating the disconnector will have if i have 14 MW, 11 kV generator and when taken to HV side of 11/132,the current rating will be: 61.24 Amps. what will be the disconnector current rating? I think disconnector does not have short circuit rating.

Regards,

 

[RRaghunath]

Disconnector rating at 132kV would have been standardised based on maximum rated 132kV feeder. Thus, the rating could be something like 1250A.
When it comes to short circuit rating, disconnector doesn't have short circuit make or break rating but it does have short circuit withstand current rating. This will be same as busbar rating in general, something like 25kA, 31.5kA or 40kA and duration of 1 or 3sec.

 

[Mlmlzx]

but the attached drawing is showing 1250 Amps as circuit breaker rating (40 kA for 1 sec) and 800 Amps as disconnector rating. I am interested how this 800 Amps was selected.

 

[jghrist]

It was probably the minimum standard size for the voltage.

 

[RRaghunath]

As I said if your busbar rating is 800A and if 800A rating is available for disconnector at 132kV, there is no need to choose higher rating. Isn't it!