ECN Forum Forums General Topics of the Trade General Discussion Area Strange Voltage Setup

"the concept of an electric-powered generator always makes me chuckle"

Don't laugh too hard, it may be the future of generation by manipulating efficienties. I had the idea in a science class when I was a kid (You know the free energy dream), and recently read a research artical on it being studied now. (Cant find the artical...) But the concept was operating generators as rotating transformers to stabalize load and PF when using wind, solar or wave energy generation instead of invertors.

On a submarine those generators are what save your life. You have two motor-generator sets. One running AC motor, Dc gen charging the battery, and the other DC motor, ac Gen supplying the bus, thus keeping a good float on the battery. If you lose the AC bus, the MG's default to DC motor, AC generator, because the battery now has a higher voltage, thus current leaves it, and saves our lives.

Back to Steve's question for a minute. As noted by Larry and others, the 120V system is pretty much for convenience outlets and lighting. It's a 120V (or maybe 110V) plain delta, meaning there is no neutral. And as mentioned above, there is no bonding of any point in the electrical system to ground (hull). So the electrical systems float. You will read 120V phase to phase, and unpredictable values phase to ground because the electrical system is floating. Same with the 450V system, you'd read 450V phase to phase but unpredictable voltages between any point in the system and ground (hull).

The floating electrical system is for tactical reliability, meaning you can inadvertently have a ground occur at any one point in the system with no effect on operation. There are permanent ground detection systems in place that are operated hourly so if a ground does develop, it can be cleared quickly. Obviously a second inadvertent ground would make for a really bad day.

So imagine this for a moment - you could, if you really wanted to, cut the ground bond on a 240V delta, and the delta would continue to work fine. You would loose basic important safety features, a most serious issue, but the system would work. Shipboard systems are just like that except they have 120V transformer secondaries rather than 240V secondaries.

Shipboard circuit breaker and/or fuse panels that are 120V all have 2 pole CB's or pairs of fuses for each circuit. As I said, it's just like a 240V delta except half the voltage. With no neutral, you need to break both sides of the line.

Don't everyone freak out here - but as best I remember I thing the 3 phase color cose was: Black / White / Red.

So with no system grounding and/or neutrals to worry about, checking the electrical system is somewhat simplified. Phase to phase voltages need to be stable, equal and clean. On my boat the turbine generators and the motor generators supplied 450VAC, the operator (me) had voltage regulator adjusting knobs so one could run the voltage up or down a bit (can't remember how far). The 120V systems were supplied by stepdown transformers from the 450V bus, so a voltage spike would seem unlikely. Plus, a 20V variance on the 450V side would amount to about 5V on the 120V side. So I don't know what else there would be to check so far as the electric system goes.

We did have a static inverter, I think 120V. It had lots of problems so we did not use it. But something like that might cause enough electrical system problems to affect other components. You might ask about that - if there is one in this case.

OK - long enough for now I reckon, someone else's turn. By the way Steve, I may know you. Do you happen to work for a large LA area contractor and assigned around the Union Station area downtown? Or used to be anyway?

Radar

Nope, sure don't, I've been around the country/world a lot for a few weeks at a pop, but I'm a GS civilian DoD engineer and have only ever worked in Norfolk/Portsmouth, VA. I used to work mostly shipboard electronics, but I'm working almost exclusively on shore-side power now. (Working 100% on US navy installations and being the senior responsible engineer means never having to worry about pesky codes or inspectors, heh)

Thanks for the explanation of the inadvertant grounding, that makes a lot of sense; I don't know why I didn't think of that myself And yes, Black, White and Red are Phase A, B and C! No such standards for connector pinouts, unfortunately. Has lead to some "issues" in the past, especially when the equipment manufacturer doesn't wire their UPS to the pins their drawings say they did, then switch halfway through the production run and begin to do it "right" but don't tell anyone about it...

[This message has been edited by SteveFehr (edited 06-11-2006).]

That is also a common color code in old industrial systems for 3 phase power.
Don

Wrong Steve, Steve. I wasn't seeing there were multiples here, I was refering to the Steve that started this string (skingusmc).

Sorry for the confusion, I'll try to pay more attention next time.

Sounds like an interesting job tho. I really kinda miss the shipboard stuff and the ocean and all. Oh well, I've drifted off topic far enough.

Radar

Some old Amtrak passenger cars use 120V 3PH corner grounded delta systems. I am not sure about the Horizon , Superliner or Amfleet cars but I know that a lot of the cars that were bought from other passenger RXR are of the corner grounded varaity.

I have a 35KW gasoline egine powered generator that came off of a Naval Ship. It was built by Hobart and I can only guess its age to be somewhere in the 1930's or 1940's because of the fact that engine is a 6 cyl flathead and it just looks like it came form that era. The funny thing is that the engine has no identifying marks on it anywhere as to who made it. Is anyone familiar with any of these gensets? The generator is a 120V Delta 3 Phase, but I am not sure of the frequency whether it is 60Hz or 400Hz. I am told that you can count the number poles (just the same as in any AC motor) in the generator to determine the frequency. The generator runs at 1200rpm. What am I physically looking for inisde the generator so that I can count the number of poles? Does anyone know where there is a picture that shows me what the poles look like?

If the generator is running, and you are getting 120 volts out, a quick and dirty test method is to plug in an electric motor clock. Time the clock for a few minutes and if it is close to keeping time, it is a 60 Hz output. 1200 rpm is correct for a 6 pole 60 Hz machine. If you have or can borrow a Fluke 80 series multimeter, there is a HZ function when measuring AC Voltage.

LarryC

Kinda drifting off topic a bit here, but what would happen to the 120V (60Hz) clock if it were connected to 120V 400Hz? Kinda like a time machine??

I was thinking, if the genset was runnable, start 'er up, borrow a scope and have a look at the wave shape. Should be simple enough to tell 60Hz from 400Hz.

NOT RECOMMENDED - but from my personal experience, inadvertant touching of the hot leg on a 400Hz source hurts a lot less than the same 120V 60Hz - more skin effect I think, less current penetration thru the skin.

Radar