Phase failure relay/Auto change over

[WaterSparky]

I was wondering, I'm not at work so can't ask one of the blokes, but I have been looking in auto change over switches, on supply loss how are the contactors switched as obviously the supply has been lost. Is this done off the generator batteries/sustained supply (UPS) ? Please I'm only an apprentice so just trying to increase my understanding.

Also I was thinking at the end of the day, looking into a simple relay could this not be used as just phase failure for single phase and only as a means as if the supply is lost, of course would not work for under over voltage etc, but this would work otherwise?

Again an apprentice go easy.

 

[Wiresandthings]

NC and NO contacts held in or out by the mains, when the mains drops, function as designed is brought into play!! Probably a bit more complex than that with voltage sensing etc

Im not a generator expert but im sure someone on here is

 

[guest119]

Phase failure relay monitors the 3 phases and the voltages supplied.
Loose any phase or go under voltage and the coupler (buscoupler) drops out because the volt free contacts of the phase fail relay, having a control circuit, can no longer hold it in.
Coupler dropping out closes aux connections (start signal) of a multicore from the generator (battery voltage).
Generator starts and comes up to speed and supplies the load.
3 relays wired for control would work but as you say not useful for a pre determined under voltage.

 

[Robotstar5]

Some info on 3 phase monitoring relays here

 

[WaterSparky]

Cheers guys for the help might try and build one in my spare time at work! Might be useful when we start getting all these power cuts!

 

[Brightspark2]

I was wondering, I'm not at work so can't ask one of the blokes, but I have been looking in auto change over switches, on supply loss how are the contactors switched as obviously the supply has been lost. Is this done off the generator batteries/sustained supply (UPS) ?

If there are no contactors and its an auto change over switch, the motor to operate the change over switch and panel can be fed from the generator batteries as you rightly guessed.

 

[Knobhead]

You have to be careful with auto change over.

There has to be a clean break from the DNO supply before the generator connects. A delay is needed for the generator to run up to speed before it connects to the system.
The time delay should be taken up by the UPS unit.

Is this an “I’m interested question?” or “real life?”

 

[WaterSparky]

Well nearly every site I work at has an auto change over panel and generator. Now im at work and talked to them about it they have said all you've said and more. Yes this is real life but I don't really make the panels, just maintain. So just intrested in their workings. I was told that most of the control is sustained by the UPS and then the PLC controls the rest of the plant coming online usually on the larger sites.

 

[guest119]

Every day is a school day, even for us.............. jurassic sparks.

Boydy

 

[johnboy6083]

On our pumping stations with auto-changeover, the Genny start sequence is initiated by a phase failure relay. This in turn operates a delay timer, which after a predetermined time, will then close the Genny start contacts, and open the mains incomer breaker.
The Genny starts, and when the phase failure relay on the Genny senses voltage on the Genny incomer, the Genny incomer will then close. The Genny will then run.

Once the mains is restored to site, another delay timer (fed from the phase failure relay) will operate the Genny stop, and open the Genny incomer. The mains incomer will then close after a short delay.

 

[steve50]

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