Automatic transfer switch

[Shawnmankc]

I'm new to the forum so I'm not sure if I'm posting this in the correct spot or not but here it goes.

I'm doing a yearly PM on an ASCO 7000 series, closed transition ATS. 480 v, 200 a, 4 pole. Everything checks out OK. While still bypassed to normal, I rack the TS from isolation to test. I perform a local test via the controller. The TS transfers from normal to emergency, and then from emergency to normal perfectly. I then rack the TS back into auto and perform one final transfer test. As soon as the emergency contacts close, the 200a emergency supply breaker trips and the TS switches back to normal. A "blink" did occur on the load. I re-check everything and try it again with the same result. The kicker is there is only about a 6 amp load on all three phases, so inrush current shouldn't be an issue. I'm stumped because if it works in test, it should work in auto. I understand in auto, you are actually transferring the load, but, in either case, it's the same voltage and phase angles being sampled during the passive synchronization process. Any ideas?

 

[Canton]

I'm new to the forum so I'm not sure if I'm posting this in the correct spot or not but here it goes.

I'm doing a yearly PM on an ASCO 7000 series, closed transition ATS. 480 v, 200 a, 4 pole. Everything checks out OK. While still bypassed to normal, I rack the TS from isolation to test. I perform a local test via the controller. The TS transfers from normal to emergency, and then from emergency to normal perfectly. I then rack the TS back into auto and perform one final transfer test. As soon as the emergency contacts close, the 200a emergency supply breaker trips and the TS switches back to normal. A "blink" did occur on the load. I re-check everything and try it again with the same result. The kicker is there is only about a 6 amp load on all three phases, so inrush current shouldn't be an issue. I'm stumped because if it works in test, it should work in auto. I understand in auto, you are actually transferring the load, but, in either case, it's the same voltage and phase angles being sampled during the passive synchronization process. Any ideas?

It looks like something with the synchronization of the two sources during the closed transition.

 

[ATSman]

I am not sure about the ASCO CT switches but the GE-Zenith CT models have a feature to protect against "extended paralleling time." This is a condition where the source that the ATS is transferring out of stays connected for more than 325 ms. A signal is sent to shunt trip the emergency source breaker to prevent damage to the generator (motoring.) This may be what is happening in your case.
You may ask well why doesn't it happen in the test position? Answer: this feature may be bypassed in test mode.
That fact that you say a blink did occur (lights blinking?) during transfer tells me that the ATS is not operating in closed transition (CT) mode properly. Was this ATS operating properly before you did the PM? It may have always had this problem.
Go to the emergency source breaker and see if you can see the shunt trip wires coming out of the side of breaker.
If so then disconnect them and try the test.
Another thing you can try is to switch from CT mode to open transition mode (break-before-make) and perform the test. The GE-Z models have a toggle switch to choose between modes. If the breaker doesn't trip then there is a problem in the CT circuit.
I keep going back to the blink on transfer. CT transfer is a seemless make-before-break transfer of load and you should not see fluorescent lights blink if fed from the ATS.