Re: Automatic Transfer Switch (ATS)
I have maintained many Automatic Transfer Switches, but I can?t answer your question.
How long does ATS Maintenance take? - depends on many things. Can the load be shut down? Are temporary power circuits required to maintain critical loads? How old is the switch? How much wear is there on the parts? Are there any operating problems that require repair? How dirty/clean is it? What is the rating? (A 100 Amp, 120 V ATS is a small job, a 4000 Amp, 480V ATS is a larger job.) What is the emergency source and is it in good condition? What are the risks of a problem during maintenance?
Best thing to do is find a company that does ATS maintenance and have them give you an estimate. Some electrical contractors specialize in this as do many NETA firms.
How does an ATS work? Check the manufacturer's websites for some good information, (Cutler Hammer, ASCO, Russell Electric, and others).
Basically an ATS has controls that monitor the normal power source and switch the critical load to a generator or alternate source when problems occur. When power fails, the control panel waits (usually 3-5 seconds) to see if power is coming back, then sends a start signal to the generator. It switches load to generator power when the controls sense the generator is at the right speed and voltage. When normal power returns, the controls monitor the normal source for a while (1-30 minutes) to make sure it is stable, then switches the loads back to normal power. Most ATS?s then run the generator for a short (30 minute) cool down period and shut down the generator.
The actual transfer or switching can be done using a single coil mechanism and linkage that opens the normal source contactor and closes the emergency source contactor, or it may use two operating coils or two electric actuated circuit breakers. Each type has its own maintenance needs and issues.
Since you wouldn?t need an ATS unless you have a critical load and the ATS always feeds the critical load, it is usually difficult to get managers to agree to shut down the critical loads even for a short time to maintain the ATS. But it is important to make sure the ATS is maintained and can do its job, or you will loose that critical load for sure.
A local hospital maintenance manager would not shut down an ATS for maintenance even though an infrared scan identified some problems and the ATS had not been tested or maintained for some time. A month later an unrelated fire took out the utility service and the ATS failed. The stress during the blackout gave the manager a heart attack. He ended up in the ER being cared for under flashlight. Fortunately, he lived but I don?t know if he kept his job. We never got a contract for ATS maintenance either.
Good Luck,
Bob Wilson
