Generator change-over...

[sponge23]

Hi I work on a site where we have generator back-up, so if the power goes down we can change-over to the generator. The problem we have is knowing when the mains is back on.
What I want to do is have a light that turns on when the mains comes back on - on a timer, for about an hour after the power comes back on.
So I was thinking of taking a feed from the mains side of the changeover, then circuit protection. Just not sure how to control the timer. Any thoughts would be greatly appreciated.

Thanks.

 

[johnboy6083]

Use a phase failure relay, that controls a delay on relay. So in other words the power stays on for an amount of time, then the mains can be restored, the Genny can idle and stop.

 

[sponge23]

Thanks very much. That is just what I need!

 

[Engineer54]

What I want to do is have a light that turns on when the mains comes back on - on a timer, for about an hour after the power comes back on.


​

If you have an ATS, it should return to prime power automatically when power returns, normally after a short time delay. That's why they call it ...Automatic!! lol!! Why you would want the generator to run-on for an hour after prime power has been restored is beyond me....

If you have a MTS, then a power failure, or under voltage relay combined with a timer and a bell/light is the way to go, but again, not timed for an hour, 5 or so minutes is more than enough for your needs....

 

[johnboy6083]

I was on site to install some lighting, and the power kept failing. The Genny would start, then the power would return, then 5mins later would drop out. I ended up running the site on the Genny set in manual, as the the existing lighting turning on and off was doing my trolley in!

 

[Darkwood]

You need a synchronising automated changeover unit ....this monitors the power and the waveform and mergers both mains and genny power together before dropping the power off the genny. They are not cheap and they are often used in hospitals where power interruption could be a disaster to life support systems.... Although never manually tamper with these units as I know of an Hospital genny that ripped itself out of the floor and through a wall when an 'engineer' push in the contactor manually as the phasing was out of synchronous to the mains....... I suspect this is the same system E54 has mentioned.....................hold this thought im looking into it it might not be an option you can use!

 

[Engineer54]

You need a synchronising automated changeover unit ....this monitors the power and the waveform and mergers both mains and genny power together before dropping the power off the genny. They are not cheap and they are often used in hospitals where power interruption could be a disaster to life support systems.... Although never manually tamper with these units as I know of an Hospital genny that ripped itself out of the floor and through a wall when an 'engineer' push in the contactor manually as the phasing was out of synchronous to the mains....... I suspect this is the same system E54 has mentioned.

Nope, and i have never seen or know of a system that merges prime and Gen power together, before dropping the generator out. And hospitals have been my main concern now for a good many years!! Can't see any point to it either as once prime power has returned and stablised, dropping the generator out is going to be the same!!

If you have a link to such a system, please post it up, i'd be very interested to see how this system works??

 

[sponge23]

I didn't want the genny to stay on for an hour after, just the light. The idea is to alert us when the mains is back on, so we can switchover.
It's all manual switchover. In an ideal world I would upgrade it to automatic, but my company are simply not going to fork out for it.
Thanks for the replies.

 

[Knobhead]

You need a synchronising automated changeover unit ....this monitors the power and the waveform and mergers both mains and genny power together before dropping the power off the genny. They are not cheap and they are often used in hospitals where power interruption could be a disaster to life support systems.... Although never manually tamper with these units as I know of an Hospital genny that ripped itself out of the floor and through a wall when an 'engineer' push in the contactor manually as the phasing was out of synchronous to the mains....... I suspect this is the same system E54 has mentioned.

I’d like to see this. I could see the DNO’s kicking up a fuss about it.

 

[Billythekid]

I’d like to see this. I could see the DNO’s kicking up a fuss about it.

Indeed, only once have I seen two synced supplies. This was with the DNO's SAP present at all times, and was done because of extremely difficult circumstances. This was also using another TX, not generator set. It'd be a brave man to "rack" that in!

I hope this C/O has electrical and mechanical interlocks-else someone's getting hurt

 

[Knobhead]

 

[Knobhead]

The place I severed my apprenticeship had its own power plant and an intake from the NWEB. By using dual bus-bar 11KV boards the two supplies could be used, but never inter-connected.

I’ve still got the maintenance and installation manuals for the Reyrolle Class B switch gear.

 

[Billythekid]

The design never intended to allow inter-connection (bus-couplers, castells, etc.). But when you're caught with your trousers down, things can (and often do) have to be implemented :juggle:.

The DNO was really understanding and helped us out of our "up the creek" situation :wings:.

 

[DPG]

Reyrolle, Asea Brown Bavari, Cast iron switchgear, black & white sketches in old electrical books, ooooooh. I'm getting excited. Daz

 

[Darkwood]

@E54 and Tony 2.5 MW Mini Power Station MISC06, I may have got my wires crossed (pun intended) if its not permissible to do so but im sure while it was been discussed I was told power was switched back to mains uninterrupted and synchronisation was needed before the panel will do the swap which was all automated. Im open to correction as I was told this second hand but it does seem plausible. The link shows such a system that synchronises with other genny's as well as mains.

 

[Billythekid]

@E54 and Tony 2.5 MW Mini Power Station MISC06, I may have got my wires crossed (pun intended) if its not permissible to do so but im sure while it was been discussed I was told power was switched back to mains uninterrupted and synchronisation was needed before the panel will do the swap which was all automated. Im open to correction as I was told this second hand but it does seem plausible. The link shows such a system that synchronises with other genny's as well as mains.

I'll get my coat :smartass:.

I've seen centralized UPS's working in conjunction with gen set via auto C/O, but never anything like this.

How can it possibly maintain synch, I'm stumped?

 

[Darkwood]

Yes apologies probably a bit extreme as a option but just to note they exist and are out there.

 

[Knobhead]

A bit OTT for keeping the office light on

 

[Darkwood]

Ill admit Tony deffo OTT but have been told of these systems a few times and although ive never worked on them I know a few places using them so assumed they were more common place but obviously not from your replies ... the link probably is misleading as its in the Mw range but Kw systems available and yes close communication with DNO is required when planning and installing. The situation where a so called Electrical maintenance Engineer was showing a new collegue how to test the system was at a local hospital to us and while waiting for synchronisation with the mains he thought the contactor was faulty and proceeded to say "this happened last time" on pushing it in manually the out of sequence mains hit the genny like an instantaneous brake meaning all that inertial force went into ripping it up from the floor and through the wall..... nearly killed everyone in room....