ECN Forum Forums General Topics of the Trade General Discussion Area 200A Auto-transfer switches

From 200kW up through 1000kW, it gets a little bigger, but doesn't really change much- the gensets are a comparable size and appearance. Our 2-3MW gens, though... freaking locomotives! Low RPM, high torque, and just tons and tons of steel. It's all medium voltage at that point, too, which makes it even more (less) fun...


[This message has been edited by SteveFehr (edited 11-14-2006).]

I too used to work on a range of military generators from 10Kw - 2MW. But mostly on the 60-500 range as they are easily portable through muck, and by paraleling you could get as much as you want - so long as they were all equal size. Biggest farm of them I ever put together was 12 500's, 6 on, 6 off mostly. All open buss-work lug to lug, it was a sight to see. No OCP at all to over-head, and UG distribution. (Field expediant AKA no parts, and no time.) Biggest generators were 2MW, usually shipped in pairs for maintenance purposes. I was telling Reno that we used to load bank those against each other by paraleling them and gradualy taking them out of phase with each other. Like two train engines in an arm wrestling match.

My specialty was "Electrical equipment repair" so my primary job was rescuing them from severe abuse after they came from the field and in/out of storage. As I mentioned before these are far less sofisticated units than what Steve has been working with - but built to take a severe beating. That said I have sent a few to the scrap yards too.

A lot of the ones I have worked on also had CT's and that dropped out the load contactor. (I haven't seen anything like that on some of the 'residential' marketed ones.) And one problem that happened on occasion was that that contactor was controlled/fed by a number of relays and contacts in series that would either drop the load, or shut the fuel off. (This also had a by-pass switch for for life or limb emergencies...) Problem was that the CT's fed an adjustable circuit that ended in an SCR that that controled the relay for over-current - it had IMO a design flaw, such that is if that circuit, SCR or relay failed there was no way of knowing, and you wouldn't know until the windings or the conductors it fed smoked. Which I have seen a few times. And smaller utility gen sets had a catch all safety circuit that operated via that dropped out at 40Hz to the fuel shut-off, with some crusty old used as a switch breaker that you could arch weld with. Which is why I have minor trust issues with over-load circuits, and shoot for fused discos. Not that I have a problem with quality thermal/magnetic breakers that we use all the time, but unlike other things - a weak link / cheap or abused breaker is often what keeps the circuit on... IMO a fused disco, or reliable breaker is the way to go.