Generator switch v. Iraq!

[Pudgygiant]

I'm with the Army in Iraq, working as a generator mechanic. My shop just got in a dead generator, if we repair it it's ours to keep. What we're thinking about doing is dropping it in next to the one running our shop as a backup. My thought was hey, we really don't do much (can't speak for anyone else in-country, but personally I'm working on that 10000 lifetime wins medal in c&c generals), why not try something nifty. I'm thinking about an auto-switchover box for the generators.

I think turning it ON would be relatively simple. There's a component called the magnetic pickup, basically uses magnets to run a couple solenoids (crank-disconnect and whatnot) and the rpm meter. I don't think it would be too tough to hook a solenoid up, when it drops past a certain point the solenoid closes and runs the starter on the other gen. The only catch is because of all the dust in the air generators sputter quite a bit over here, it's not a big thing for one to drop down to where it's not even generating power then catch itself and pick back up. But I think with a multimeter and the manual throttle I could figure out a decent limit for it.

The real problem, in my opinion, is finding a way to turn on the circuit breaker. I can't just leave it on because when the gen starts up it does this thing called flashing the field, basically sends raw voltage to the windings and gives them an initial charge. Unfortunately, however, it always jumps above the voltage it's set to put out, then settles back down, during the field flash. I'd need a way to monitor this, probably with a built-in time delay, then cut on the switch when the voltage settles down. Just for kicks let's say the switch is going to have to handle somewhere in the range of 5KW, 440V.

Is this possible? I have access to pretty much any components I want IF I can get a decent plan drawn up for it, but I don't have too incredibly much know-how.

 

[Mark R]

Time delay relay?

Use a normal relay to trigger the starter, then use a time delayed changeover?

 

[OSX]

I was thinking of something involving comparators. You could set it up so that it would drain power from an RC network when the voltage at the comparator went below a certain level. When there's power coming from the RC network, it would engage the starter motor, but when it fell below a certain level, the starter would disengage. Rather complicated to the point of pointlessness, but I like the phrase RC network.

 

[davesaudio]

you can get off the shelf stuff to do this, google
generator transfer switches or load centers or automated transfer switches or....

if thats not in the budget what are your limitations:
can you do electronics, solder ICs? access to a scope?
gotta be a relay logic solution?...

 

[brandonbull]

Must be an older generator if you still have to flash the field. I would suggest having the circuit breakers ON but place a magnetic contactor between the generator and the circuit breaker. You could install a time delay to make sure the generator picks up speed and the voltage stabilizes before picking up the load. You also want to make sure that once a generator drops off it won't automatically try to pick up the electrical load while your distribution system is energized. Unsynched generators = BAD

 

[Pudgygiant]

I should have said that this isn't really an official solution, it's not really even sanctioned. It's more like, we sit around all the time, and my section sergeant said hey, go for it, just don't break anything.

Funds are pretty much personal. I can order quite a few parts but only things that I could find on a generator, that's why I'm trying to limit it to relays and switches on the gens themselves. My thought was, since the relays we have are all triggered by 12v, tap off the batteries and drop in a resistor. 12V coming from the batteries, 5v (I got anywhere from 4-9 when it was running, so either I was getting a bad connection or it's very fickle) from the mag pickup, with a 6ohm resistor.

This is all just an idea I'm kicking around, I'm aware they make auto-switches for this, like the completely UPS's in hospitals, where it switches to a battery so you don't even have that 10 second gap where the gen is starting.

 

[brandonbull]

you would need a solenoid connected to your main distribution system. so if the power drops out, the coil would engage the starting system and then engage the field flash timer that would close a magnetic contactor connected to your electrical system.

 

[TitanDiddly]

As far as the dust in the air issue, don't they have good air filters?



Also, 5KW at 440V is only 11.x amps. If you're going to trigger it with DC voltage, just ask the auto guys to order you a starter solenoid for a hummer or something- it'll handle much more than 11A, but I'm thinking that it'll have a bigger gap, and will not have a problem with the 440V arcing the contacts. YMMV. IANAL.

 

[huberm]

it is too much work to even mess with, why dont you just get an ATP?

How about doing PMIs instead of thinking this stuff up?

 

[brandonbull]

Originally posted by: huberm
it is too much work to even mess with, why dont you just get an ATP?

How about doing PMIs instead of thinking this stuff up?

That's the way to promote thinking. We need more mindless robots. I guess this guy taking some initiative doesn't go well with the G-Dub collective.

 

[PowerEngineer]

As Brandon already pointed out, your scheme likely needs to ensure that your primary generator is seperated from the electrical system before your new back-up connects itself. Running multiple generators together requires a synchronization process involving both speed and phase angle. You might cause major damage to both generators (and attached elecrical motors) if it's botched. It's unlikely (but possible) that relatively small generators like yours have auto-synchronization circuitry.

I'm guessing that your primary generator's breaker will trip whenever it really fails (and you wouldn't want to start the back-up until it is tripped). There should be contacts available on the breaker that mirror its status. You might use a spare pair of these contacts to trigger the starting sequence for the back-up generator.

You're right that closing the breaker connecting the back-up generator might be the tough trick. I'm guessing that these breakers require your physical effort to close them (and that they store some of that as energy for tripping). If so, it will not be easy (and likely dangerous) to automate its closing.

I'd be cautious about suggestions to use a something other than the breaker to connect and disconnect the generator. The parts in any such scheme should be rated for both the expected currents and voltages. 440-480 volts is a very dangerous level, and the current levels can be much greater than normal levels when there is an electrical fault. Breakers are the way they are for a reason.

Be careful over there -- with this adventure and with everything else too!

:thumbsup:

 

[Pudgygiant]

Originally posted by: TitanDiddly
As far as the dust in the air issue, don't they have good air filters?

It's counterintuitive, but it bothers the fuel a lot more than the air. We use JP8, which is crap to start with, and then the fuelers are mostly independant contractors, and most of THEM are non-american, so what happens a lot of times is they leave the cap off, just not paying attention or not caring. Not a big deal in the states, but the dust over here is so fine that it clogs up the fuel lines quickly.

It's so bad I can't leave clothes hanging in my dresser for more than a couple weeks, they start to look dirty even if I haven't worn them.



PowerEngineer, I can get a "synch box" for them, but it won't auto-start, and it won't even synch the generators itself. It's kind of sad when I see 10 year old Volvo gens over here more sophisticated than our brand-new B-series generators. I mean yeah, ours look all futuristic with the LCD and all, but they're pretty ghetto when it comes down to it. You have to match up flashing lights to synch gens...

On second thought, though, you can close the breaker on the bravos from the LCD... I need to figure out how they do it.

 

[TitanDiddly]

Originally posted by: Pudgygiant

Originally posted by: TitanDiddly
As far as the dust in the air issue, don't they have good air filters?

It's counterintuitive, but it bothers the fuel a lot more than the air. We use JP8, which is crap to start with, and then the fuelers are mostly independant contractors, and most of THEM are non-american, so what happens a lot of times is they leave the cap off, just not paying attention or not caring. Not a big deal in the states, but the dust over here is so fine that it clogs up the fuel lines quickly.

It's so bad I can't leave clothes hanging in my dresser for more than a couple weeks, they start to look dirty even if I haven't worn them.



PowerEngineer, I can get a "synch box" for them, but it won't auto-start, and it won't even synch the generators itself. It's kind of sad when I see 10 year old Volvo gens over here more sophisticated than our brand-new B-series generators. I mean yeah, ours look all futuristic with the LCD and all, but they're pretty ghetto when it comes down to it. You have to match up flashing lights to synch gens...

On second thought, though, you can close the breaker on the bravos from the LCD... I need to figure out how they do it.

How many microns do the fuel filters filter to?

Also, do you use UPSs to keep power on when the generator bogs down?