Cogeneration, ATS and Emergency Generator

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Tainted

Tainted

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New York
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Engineer (PE)
There is an ATS, the normal side is being fed by the utility and cogen. The emergency side is being fed by emergency generator.

My question is:

If there is no utility power, I would like it to switch to emergency power. The problem is if the cogen is energizing the normal side, then the ATS might not switch to emergency power, how do I ensure ATS switches to emergency when there is no utility but the cogen is active?
 
You would have to sense actual utility voltage on the incoming of your utility/cogen switchboard or switchgear rather than just voltage present on the normal side of your ATS.
 
d0nut said:
You would have to sense actual utility voltage on the incoming of your utility/cogen switchboard or switchgear rather than just voltage present on the normal side of your ATS.
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How can that actually be wired to the ATS? do you just put a current transformer on the utility side to sense the voltage? will that be code compliant? what if the ATS is far away from the current transformer?
 
Now that I think more about the scenario, what I described above would not start the generator if the feeder breaker opened but utility power was still available so it wouldn't work for your scenario. You would need to use inputs from both voltage present at the utility and voltage present at the normal side of the ATS with relays arranged for a logical OR (either source missing) input. I can think of a couple of ways that the relay logic could work, but it would probably be more advantageous to talk directly to the generator or transfer switch manufacturer to see how to accomplish what you are wanting with their equipment. It looks like an uncommon arrangement, but not an impossible one.
 
Just to be clear, it sounds like the OP is referring to 2 power sources in parallel not cogeneration. Cogeneration is combined heat and power (CHP) which is a different animal.
 
d0nut said:
Now that I think more about the scenario, what I described above would not start the generator if the feeder breaker opened but utility power was still available so it wouldn't work for your scenario. You would need to use inputs from both voltage present at the utility and voltage present at the normal side of the ATS with relays arranged for a logical OR (either source missing) input. I can think of a couple of ways that the relay logic could work, but it would probably be more advantageous to talk directly to the generator or transfer switch manufacturer to see how to accomplish what you are wanting with their equipment. It looks like an uncommon arrangement, but not an impossible one.
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I am not sure if that will even work, the cogen backfeeds to the utility and powers the entire building. So even if the utility is not present, there will still be voltage there from the cogen
 
texie said:
Just to be clear, it sounds like the OP is referring to 2 power sources in parallel not cogeneration. Cogeneration is combined heat and power (CHP) which is a different animal.
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Cogen and utility are providing power to the entire building through a common bus, so it is considered paralleled power supply
 
How is the cogen isolating when utility is lost? I don’t think the utility would be too happy with the backfeed to their lines if they tripped out for any reason. Does it open and close the utility feed breaker automatically? If so, it probably has a dry alarm, or maybe position contact that could be used as a utility loss sensor? That can be used as an input to the transferswitch if it has, or can have a forced transfer option. Wouldn’t be too bad expensive to do, unless getting from the cogen controls to the transferswitch is not practical. Even then, wireless or internet based control is an option.
 
You won't sense loss of utility unless you have a directional overcurrent (67) relay. With a 67 relay, the cogen plant can be tripped off line as soon as it starts to export power off site. The utility probably already requires this and you might have some multifunction relay like an SEL-351 on the cogen plant that does it. When the utility and cogen are off line, your ATS will work as usual.
 
JoeStillman said:
You won't sense loss of utility unless you have a directional overcurrent (67) relay. With a 67 relay, the cogen plant can be tripped off line as soon as it starts to export power off site. The utility probably already requires this and you might have some multifunction relay like an SEL-351 on the cogen plant that does it. When the utility and cogen are off line, your ATS will work as usual.
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And if it was desired to keep the cogen plant running through a utility outage, there would most likely be a control scheme that would open the main (utility) breaker upon loss of utility power and probably open several feeder breakers to shed enough load so that you wouldn't overload the cogen plant. That same signal could be used to start the emergency generator and force the ATS to transfer.
 
Tainted said:
There is an ATS, the normal side is being fed by the utility and cogen. The emergency side is being fed by emergency generator.

My question is:

If there is no utility power, I would like it to switch to emergency power. The problem is if the cogen is energizing the normal side, then the ATS might not switch to emergency power, how do I ensure ATS switches to emergency when there is no utility but the cogen is active?
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Why? Anything you attempt is probably going to bypass the emergency functions of the ATS. For example, what happens if the generator doesn't start? Is the ATS going to just sit there powered from a dead source while the Cogen chugs away supplying all the non-emergency loads?

If you really want the ATS to go to generator every time the utility cuts out, you should just feed the ATS with utility only power, and not connect the cogen.

I understand that might not be an option if there isn't a separate utility bus.
 
steve66 said:
Why? Anything you attempt is probably going to bypass the emergency functions of the ATS. For example, what happens if the generator doesn't start? Is the ATS going to just sit there powered from a dead source while the Cogen chugs away supplying all the non-emergency loads?

If you really want the ATS to go to generator every time the utility cuts out, you should just feed the ATS with utility only power, and not connect the cogen.

I understand that might not be an option if there isn't a separate utility bus.
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Usually a transferswitch will not transfer if the second source is not available (stays on preferred source, even if it is also dead).
 
hillbilly1 said:
Usually a transferswitch will not transfer if the second source is not available (stays on preferred source, even if it is also dead).
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Yes, but by making the ATS transfer when it normally wouldn't (when there is still power on the normal side), one has to be careful this "override" doesn't affect what a transfer switch would "usually" do.
 
Actually, thinking about this a little more, I would contact an ATS manufacturer, and ask them how this can be accomplished. They might be able to do this the proper way, by giving you "request to transfer" inputs on the ATS.

But you would still need a way to sense the loss of utility power.
 
hillbilly1 said:
Usually a transferswitch will not transfer if the second source is not available (stays on preferred source, even if it is also dead).
Click to expand...
You are correct, an ATS is designed not to transfer to a dead bus, of course, if it does not involve a load shed (off gen) scheme where if, on gen power, it is commanded to transfer back to a dead utility bus.
 
JoeStillman said:
You won't sense loss of utility unless you have a directional overcurrent (67) relay. With a 67 relay, the cogen plant can be tripped off line as soon as it starts to export power off site. The utility probably already requires this and you might have some multifunction relay like an SEL-351 on the cogen plant that does it. When the utility and cogen are off line, your ATS will work as usual.
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thanks for your input guys, it helps me out a lot.

So what really cought my eye is the application of a directional relay.

Let’s say you have utility and cogen feeding the same wire, you put a coil to measure the current in the wire. It will only tell you the magnitude of the current but will not tell you how much is being contributed to the utility vs the cogen separately. Will a directional relay help with this?

does the cogen already have the mechanism to sense utility power activity?
 
What are you referring to with the term "cogeneration"? If it is PV (solar) or any other current source (as opposed to a voltage source), it should be supply side interconnected on the utility side of the ATS. Otherwise it could backfeed the generator, which is bad news for most generators.
 
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