jstelly
Electrical
- Jun 11, 2009
- 2
I have several definite-purpose circuit breakers type SPS2-145-50-1 associated with a 115 kV bus system. There are also three 50 MVA capacitor banks connected to the same bus as these breakers. The breakers in question do not switch in the cap banks but hang off of the same bus. My concern is if one of these breakers were to ever try to close into a grounded fault (such as a ground switch left closed) with all three cap banks energized, would they be sufficiently sized? I have done some calculations for the described fault and listed below.
The Ipk x f product calculated is approximately 2.1 x 10^7 . According to Std. C37.06, the product must be below 2 x 10^7 for a general purpose breaker. Anything above this rating requires a definite purpose breaker as is applied.
The calculated frequency is 981 Hz which is well within the limits of a definite purpose circuit breaker.
The calculated peak amps is 21080 A. This is considerably greater than the 16 kA transient inrush peak associated with definite purpose breakers. Does this 16 kA rating apply to this situation, or is this just for normal back-to-back switching duty?
The definite purpose breakers also have a rated short circuit current of 50 kA on its nameplate. So which rating would apply in this situation? Is it simply a mater of whether or not the Ipk x f product is above 2 x 10^7? Below this number its 50kA, and above the threshold it can only handle 16kA.
The Ipk x f product calculated is approximately 2.1 x 10^7 . According to Std. C37.06, the product must be below 2 x 10^7 for a general purpose breaker. Anything above this rating requires a definite purpose breaker as is applied.
The calculated frequency is 981 Hz which is well within the limits of a definite purpose circuit breaker.
The calculated peak amps is 21080 A. This is considerably greater than the 16 kA transient inrush peak associated with definite purpose breakers. Does this 16 kA rating apply to this situation, or is this just for normal back-to-back switching duty?
The definite purpose breakers also have a rated short circuit current of 50 kA on its nameplate. So which rating would apply in this situation? Is it simply a mater of whether or not the Ipk x f product is above 2 x 10^7? Below this number its 50kA, and above the threshold it can only handle 16kA.