ThePunisher
Electrical
Hi all,
I have this dilemma of a system for a 575 V, 3 phase pump motor with starter fed directly from a 600 V, 3 phase generator.
The generator is rated 56 kW, 3 phase, 60 Hz but the generator circuit breaker is 200 AT MCCB, Square D type JD. The power cable between the generator and the starter is only 3C-4AWG, RECK, 1000V.
1. Circuit breaker is oversized and would require 70AT MCCB to protect the 4AWG cable. Since the generator is only rental and we have schedule issues, we decided to simply add the 70 AT MCCB between the generator 200AT breaker and the starter. We will install the 70AT MCCB 3 meters away from the generator.
2. When we ran arc flash study, there is no issue between the 70AT MCCB and the power panel.
3. However, the 200AT generator circuit breaker's fault clearing time (FCT)for generator contribution of only 560A is resulting to a large arc flash energy at the line side of the 70AT MCCB.
Someone informed me that generators normally are not able to sustain the arc current and should not be an issue. However, my dilemma is that HOW would we simulate that in ETAP? How much FCT we would consider (I was thinking to assert 2 seconds), but I don't have any basis.
I believe, the AVR would simply give up during fault conditions and shutdown the generator...but I do not have any data on how long would the generator shifts from substransient to synchronous and shut down. If I have that duration, I may consider that time as FCT and assume sustained subtransient current to be conservative. I was thinking of checking the ETAP typical decrement curve but still the FCT total must be assumed for the generator.
I appreciate any help or guidance. Thank you very much.
I have this dilemma of a system for a 575 V, 3 phase pump motor with starter fed directly from a 600 V, 3 phase generator.
The generator is rated 56 kW, 3 phase, 60 Hz but the generator circuit breaker is 200 AT MCCB, Square D type JD. The power cable between the generator and the starter is only 3C-4AWG, RECK, 1000V.
1. Circuit breaker is oversized and would require 70AT MCCB to protect the 4AWG cable. Since the generator is only rental and we have schedule issues, we decided to simply add the 70 AT MCCB between the generator 200AT breaker and the starter. We will install the 70AT MCCB 3 meters away from the generator.
2. When we ran arc flash study, there is no issue between the 70AT MCCB and the power panel.
3. However, the 200AT generator circuit breaker's fault clearing time (FCT)for generator contribution of only 560A is resulting to a large arc flash energy at the line side of the 70AT MCCB.
Someone informed me that generators normally are not able to sustain the arc current and should not be an issue. However, my dilemma is that HOW would we simulate that in ETAP? How much FCT we would consider (I was thinking to assert 2 seconds), but I don't have any basis.
I believe, the AVR would simply give up during fault conditions and shutdown the generator...but I do not have any data on how long would the generator shifts from substransient to synchronous and shut down. If I have that duration, I may consider that time as FCT and assume sustained subtransient current to be conservative. I was thinking of checking the ETAP typical decrement curve but still the FCT total must be assumed for the generator.
I appreciate any help or guidance. Thank you very much.