Prblem with ASCO ATS
This could be part of the normal behavior of the ATS. Many ATS are set up to allow the switch mechanism to sit in the "neutral" position for a time delay (as much as a minute) so that things like large motors, pumps, etc to wind down so that they don't get powered up at full speed. Here is how I would troubleshoot your ATS:
1) With the Commercial power on and the ATS in Normal, start the generator and make sure that the power at the Emergency terminals of the ATS is the correct voltage and frequency, if this is a 3 phase system also make sure that the phasing matches the commercial power side.
2) Turn the generator off, make sure it's in off not auto. Turn the commercial power off. Then manually operate the ATS transfer mechanism (there is usually a little handle for this), check continuity of the poles of the transfer mechanism to make sure that it's really making and breaking contacts where it's supposed to. While you're doing this you need to check the limit switches at both sides of the transfer mechanism, These switches are how the ATS controller "knows" what state the mechanism is in, they sometimes get out of mechanical adjustment and on rare occasions break and have to be replaced.
3) Once you've satisfied yourself that the transfer mechanism is operating correctly, set it to the Normal position and turn the commercial power on. Switch the generator into Auto so that the system is in it's Automatic mode. Find the manual for the ATS if possible and locate and record all of the adjustable time delays, I often write down the time values we want inside the door of the ATS.
4) With your stopwatch or sweep second hand wristwatch at the ready, start the Test function of the ATS and time out the various operating states as the system goes thru them. In general your ATS should do something like this:
a) You hit the test function, the system simulates a Commercial outage and begins a transfer sequence. On many systems there is an adjustable time that the Commercial power has to remain off for anything to happen, this is Time Delay Start.
b) The ATS closes the contact that tells the generator to start. Then it waits until it sees correct power at the Emergency terminals of the transfer mechanism. When correct Emergency power is available, the ATS controller fires the transfer mechanism to put it into its neutral position. After an adjustable time delay (Time Delay Neutral), the controller fires the mechanism again to put it into Emergency position. Some mechanisms aren't designed to do this "stopping in the middle" feature and so there is only the one action by the controller to get from Commercial to Emergency position, it's also worth noting that on mechanisms that can stay in the neutral position the delay could be 0 so the switch will transition as fast as it can.
c) The system is now suppling the load from the generator. Some ATS require you to interact with the test at this point to get back to the Automatic mode, read the fine manual. In any case there will be a delay from the time the ATS detects correct power at the Normal terminals until it starts the sequence to get back to Auto, this delay is called Time Delay Emergency to Normal. You want this time to be just long enough to keep from making false transfers, but not so long that you waste fuel, most places are something like 15 - 30 minutes.
d) If there was a delay in the neutral position going to Emergency, there ought to be one coming back to Normal. Keep in mind that this delay isn't about the source of power, it's about the load.
e) Once the switch is in the Normal position, the ATS should keep the generator running for a time (Time Delay Cooldown), to allow the prime mover (engine) to return to a safe to shut down condition. On small air cooled engines this can be 0, on very large diesel engines it can be as much as 30 minutes.
f) The system is back in Automatic mode waiting for a power fail.
5) If the ATS can perform a transfer test as above correctly, it should be able to operate just the same way during a real outage. One can and should be able to demonstrate this by operating a disconnect (switch, breaker, etc) at the Commercial power side of the ATS.
If your ATS doesn't pass the transfer test as above, look for (in order of probability)
Incorrect power from the generator.
Broken or missadjusted limit switches in the transfer mechanism.
A mechanically broken transfer mechanism.
A bad controller in the ATS.
Apr 07, 2009 |
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