Quarterly Generator + UPS testing

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Golden Boy

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I have a customer who has a large load and is inquiring about testing his entire system for power reliability. They have a Utility/Generator - ATS - UPS system. They want to ensure proper load transfers and the synchronizing on the UPS. The questions are:

"Does operating the Main Utility Disconnect prior to the ATS regularly for maintenance reduce its rating over time?"
"If so, how many operations?"
"Is it safe?"

Also the safety note, I recommended proper Arc Flash PPE to operate the MAIN OCPD to simulate the utility outage.

Any advice for this customer?
 
Golden Boy said:
I have a customer who has a large load and is inquiring about testing his entire system for power reliability. They have a Utility/Generator - ATS - UPS system. They want to ensure proper load transfers and the synchronizing on the UPS. The questions are:

"Does operating the Main Utility Disconnect prior to the ATS regularly for maintenance reduce its rating over time?"
"If so, how many operations?"
"Is it safe?"

Also the safety note, I recommended proper Arc Flash PPE to operate the MAIN OCPD to simulate the utility outage.

Any advice for this customer?
Click to expand...

You should be able to program a generator run with load into the transfer switch which is pretty much the ATS being told by the sensing leads that there is no power, start the generator, transfer the load, run with load, then the ATS (after a programmed time) see's that power has returned transfers back and shuts down the generator.
I would not open the main just to start the generator.
 
qcroanoke said:
You should be able to program a generator run with load into the transfer switch which is pretty much the ATS being told by the sensing leads that there is no power, start the generator, transfer the load, run with load, then the ATS (after a programmed time) see's that power has returned transfers back and shuts down the generator.
I would not open the main just to start the generator.
Click to expand...

I also agree that the ATS should be able to be set to exercise on a certain day and time and transfer the load. As Mike well knows we have over 200 generators in operation and we have them set to exercise and transfer the load on Mondays. But we will also kill the main once every 3-4 months to make sure that every thing works as it should under real outage conditions. But, with that said, our buildings only have 200 amp services on them. If you are talking about a service that is over 400 amp then, IMPO, I would not open the main just to test the generator. Let the transfer switch do it.
 
At my last plant we had 12 back up generators. every Wednesday they ran for 30 minutes. once a month was under load. we had 2-3 power failures a year due to lighting or something similar. good test right there.
 
There are industry specs for testing and you would want to know if you are required to comply, and with what spec. Generator testing could be monthly for one hour, battery testing could be quarterly, electrolyte specific gravity and float voltage. Don't quote me, I would research what you are supposed to be doing.

I would echo the comments about not opening the main under load. There is a big difference in construction and specified expectations going from a molded case breaker to an ATS or something like a Cutler Hammer DSV. The manufacturer should be able to tell you how many operations the switch is rated for and how many at full load.

UPS batteries wear out relatively quickly and you would want a way to test for this, or change them on time as they get aged. During generator testing the UPS batteries would only carry the load 30 to 60 seconds, but if you needed 10 or 20 minutes on batteries, the batteries may not be there for that.

I would consider generator testing with the full building load to be dangerous if the load is large and critical.
 
You can also look at how much of the load needs to be covered by the generator. My last plant had separate MCCs for normal power and backed up power. The lights for a building do not need to be on a generator. the emergency lights do need to be. There are lots of things that probably don't need to be on backup power. Maybe your customer can break his load up so there wouldn't be such a high demand when it did switch over.
 
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