tim.linenbrink@ieee.org
New member
I have found a situation I?d like to hear some opinions on:
Have an Owner with a 3000A, 3PH, 480V main switchboard and a 470 kW generator connected to a 2000 A generator switchboard. The two systems are interconnected via three, 4 Pole ATSs.
On transferring from emergency back to normal, the feeder breaker supplying one of the transfer switches opens. This only happens when going from emergency-to-normal, not the other way. The feeder breaker on the normal side has GFI and is zone interlocked with the main; it does not have a ground fault indicator. The feeder breaker on the emergency side is just a thermal-magnetic molded case circuit breaker.
Here?s what has been found:
(1) The generator system, even though installed as a separately derived system, had no intentional ground. Not at the generator, not at the generator switchboard.
(2) On the transfer switch with the feeder breaker that operates, the neutrals were inadvertently switched, e.g., the normal neutral was landed on the emergency side of the switch and vice a versa. (This was easily done given then design of the switch.)
The previous engineer and electricians solution was to simply turn up the GF pickup and time delay until the feeder breaker stayed closed.
Both of the problems have been corrected.
Here?s what I suspect:
(1) When transferring from normal to emergency, the emergency system became effectively grounded to the service ground through the reversed wiring on the ATS neutral.
(2) The fact that turning up the feeder breaker ground fault ?made the problem go away? makes me suspect that the feeder breaker was seeing whatever was happening as a ground fault.
(3) When transferring from emergency-to-normal, the effective ground path is lost. This results in a transient overvoltage which the feeder breaker sees as a ground fault.
Can a GFI see a transient overvoltage?
I?d appreciate to hear any thoughts on post.
Have an Owner with a 3000A, 3PH, 480V main switchboard and a 470 kW generator connected to a 2000 A generator switchboard. The two systems are interconnected via three, 4 Pole ATSs.
On transferring from emergency back to normal, the feeder breaker supplying one of the transfer switches opens. This only happens when going from emergency-to-normal, not the other way. The feeder breaker on the normal side has GFI and is zone interlocked with the main; it does not have a ground fault indicator. The feeder breaker on the emergency side is just a thermal-magnetic molded case circuit breaker.
Here?s what has been found:
(1) The generator system, even though installed as a separately derived system, had no intentional ground. Not at the generator, not at the generator switchboard.
(2) On the transfer switch with the feeder breaker that operates, the neutrals were inadvertently switched, e.g., the normal neutral was landed on the emergency side of the switch and vice a versa. (This was easily done given then design of the switch.)
The previous engineer and electricians solution was to simply turn up the GF pickup and time delay until the feeder breaker stayed closed.
Both of the problems have been corrected.
Here?s what I suspect:
(1) When transferring from normal to emergency, the emergency system became effectively grounded to the service ground through the reversed wiring on the ATS neutral.
(2) The fact that turning up the feeder breaker ground fault ?made the problem go away? makes me suspect that the feeder breaker was seeing whatever was happening as a ground fault.
(3) When transferring from emergency-to-normal, the effective ground path is lost. This results in a transient overvoltage which the feeder breaker sees as a ground fault.
Can a GFI see a transient overvoltage?
I?d appreciate to hear any thoughts on post.