Installing a new cogen unit into existing electrical distribution. The cogen unit will also act as a generator under loss of normal power. When normal power is lost the circuit breaker(or feeder) feeding the panelboard must be opened so that we do not back feed onto the utility grid. when normal power is restored we need a 1-3 second delay and then close this circuit breaker(or feeder). Does anybody know of any control products that can accomplish this? I would use electrically operated circuit breakers but the gear has been ordered and electrically operated breakers will not fit into the gear....Cogen unit was added mid way thru construction!
automatic disconnect
- Thread starter bwyllie
- Start date
- Status
- Location
- Massachusetts
IMO, you will need something listed for this purpose as the danger to linemen is real.
This must be a common situation.
This must be a common situation.
- Location
- Massachusetts
haskindm said:
A typical ATS is not going to be able to parallel the utility and the generating plant under normal operating conditions.
a transfer switch will only switch the normal power off when there is a secondary source of power. In the proposed scheme the cogen unit feeds into the panelboard and not an ATS because this cogen unit will also be supplying power during normal operation. Thats the gig with the cogen unit, it reduces the demand on the utility.
- Location
- Massachusetts
I recommend calling these folks on the phone.
Russelectric
They may be able to provide a solution.
They make all kinds of specialty programmable switches.
Russelectric
They may be able to provide a solution.
They make all kinds of specialty programmable switches.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
Dont you just hate it when you throw away a post through operator error rather than submitting it!
Please keep us posted on how this works out.
My interest stems from once working in a building that had 3 x 300KVA cogens, whcih very nicely heated the building and reduced the power bills. They were also part of the standby power scheme, along with 2 x 2MVA diesels.
The problem is the cogens couldn't black start, or continue to deliver power in the absence of a prime source. So, when the utility dropped, the cogens, if running, stopped. The diesels started, synced up, and supplied the main bus. The cogens would then start, and connect to the main bus. When the whole lot was running, the ACB between the main bus and the essential bus would close.
That was the theory.
The twice it was needed I was there it failed to work both times. The cooling water pumps were supplied from the main bus, so until everythiung was up and running there was no cooling water. Turns out it took so long to sync that lot up the diesels overheated, and automatically shut down. So the cogens shut down. And so no standby power was ever delivered...
The switchgear necessary for this system was based on three busbars with ACBs between, a supply busbar from the utility transformers, a main busbar, to which the gensets were connected, and an essenial busbar, which fed the building. Normally the ACBs between utility and main, and main and essential were closed. When power ws lost, both opened, and the supply ACB stayed open, and the essential one closed when the gens were ready to take ther strain. Note that in this scheme there was not only an ionterruption going to standby power, but interruption going back to utility power too.
Very much like one half of MIT electrical system:
But without the left / right split busbars, no current limit reactors, and no transformers, Bus G and Bus A being the same bus, and the diesels straight onto Bus A, for full operation.
Please keep us posted on how this works out.
My interest stems from once working in a building that had 3 x 300KVA cogens, whcih very nicely heated the building and reduced the power bills. They were also part of the standby power scheme, along with 2 x 2MVA diesels.
The problem is the cogens couldn't black start, or continue to deliver power in the absence of a prime source. So, when the utility dropped, the cogens, if running, stopped. The diesels started, synced up, and supplied the main bus. The cogens would then start, and connect to the main bus. When the whole lot was running, the ACB between the main bus and the essential bus would close.
That was the theory.
The twice it was needed I was there it failed to work both times. The cooling water pumps were supplied from the main bus, so until everythiung was up and running there was no cooling water. Turns out it took so long to sync that lot up the diesels overheated, and automatically shut down. So the cogens shut down. And so no standby power was ever delivered...
The switchgear necessary for this system was based on three busbars with ACBs between, a supply busbar from the utility transformers, a main busbar, to which the gensets were connected, and an essenial busbar, which fed the building. Normally the ACBs between utility and main, and main and essential were closed. When power ws lost, both opened, and the supply ACB stayed open, and the essential one closed when the gens were ready to take ther strain. Note that in this scheme there was not only an ionterruption going to standby power, but interruption going back to utility power too.
Very much like one half of MIT electrical system:
But without the left / right split busbars, no current limit reactors, and no transformers, Bus G and Bus A being the same bus, and the diesels straight onto Bus A, for full operation.
rcwilson
Senior Member
- Location
- Redmond, WA
Synchronizing a generator with a utility can be difficult with a motor operated breaker. Motor operators may be too slow to close the contacts before the voltages swing out of synch.
I have had a few bad experiences trying to do this. The generator frequency was varying and the governor could not hold the voltages in synch long enough for a safe breaker closure. The synch check relay would send the breaker close signal but the motor operators would take a few seconds to close the molded case circuit breaker. That was enough time for the voltages to drift out of synch. No apparent equipment damage but the inrush current due to the voltage mismatch would sometimes trip the generator or main breakers on instantaneous.
If the generator governor can hold frequency steady and the motor operators can close the CB in a few cycles, the system could work.
I have had a few bad experiences trying to do this. The generator frequency was varying and the governor could not hold the voltages in synch long enough for a safe breaker closure. The synch check relay would send the breaker close signal but the motor operators would take a few seconds to close the molded case circuit breaker. That was enough time for the voltages to drift out of synch. No apparent equipment damage but the inrush current due to the voltage mismatch would sometimes trip the generator or main breakers on instantaneous.
If the generator governor can hold frequency steady and the motor operators can close the CB in a few cycles, the system could work.
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