Bypass-isolation ATS question

[Maintainman23]

So we have a planned shutdown at one of our facilities. The ATS has a bypass switch for both emergency power and normal power. If I get the generator running up to speed before the shutdown can I bypass to generator power without loss of power to the building? Or will there still be a loss of power as it transfers from utility power to the generator?

 

[don_resqcapt19]

Unless there is a provision for "make before break" on the bypass switch you cannot do that. You have to close the two systems together when there is less than 5 degrees difference between the sine waves of the utility and the generator. The "make before break" or closed transition type switches monitor both systems and automatically close the systems together when the two systems are close enough in sync to not cause a serious issue.

 

[Maintainman23]

Unless there is a provision for "make before break" on the bypass switch you cannot do that. You have to close the two systems together when there is less than 5 degrees difference between the sine waves of the utility and the generator. The "make before break" or closed transition type switches monitor both systems and automatically close the systems together when the two systems are close enough in sync to not cause a serious issue.

Okay so if it is not make before break, I am better of just shutting off the main disconnect and letting the ATS do its thing?

 

[jim dungar]

If the generator is already up to speed, it may save you several seconds of blacked out time that eould have been experienced waiting for the generator to start. But you will still have some period of outage as Don mentioned.

 

[texie]

So we have a planned shutdown at one of our facilities. The ATS has a bypass switch for both emergency power and normal power. If I get the generator running up to speed before the shutdown can I bypass to generator power without loss of power to the building? Or will there still be a loss of power as it transfers from utility power to the generator?

As Don pointed out this will not work for you. I'll just add that an ATS does does the overlap he is referring to is called a closed transition ATS. Also made are closed transition ATS that also include a bypass. Closed transition ATS are not very common due to the cost and complexity and some say decrease reliability due to the added complexity. But they have their place in some installations.
For your situation you are probably wishing you had a closed transition ATS.