# A/C Generator Help

#### rcflier00

Joined Jul 25, 2005
2
im need some help on a 30 kw gen. i have voltage going to the exciter stator when i energize the gen but i only get low hertz and very low volts. when i release the switch i get zero hertz zero volts. im learning how to work on gens by OJTso please bear with me. the exciter circuit checks good to the stator, it acts like the wants to build a field and then drops off. can a winding that checks good for resistance fail when voltage is applied? i probally did not give enough info for you so i hope you can give me some direction in this. the only thing i have for trouble shooting is a DVOM. thanx

#### Erin G.

Joined Mar 3, 2005
167
Is this a home built generator, or something off the shelf that you're trying to get to work?

[/QUOTE]i have voltage going to the exciter stator when i energize the gen but i only get low hertz and very low volts.
The excitor should be providing the field voltage for the gen. The stator (armature on a gen) windings is where you usually take the load from the gen. What is the power source for the excitor? Remember that frequency is not a function of voltage, though a voltage must be present to measure the freq. Use this formula,

F=NP/120

where F is the frequency, N is the speed of the gen and P is the number of poles in the gen. So if you have a 2 pole gen spinning at 3600 RPM,...

F= 3600*2/120
F=7200/120
F=60 HZ

If you are experiencing a low freq, you are probably not spinning the gen fast enough since in this formula, speed is the only thing can change. You may not be measuring it properly. Are you using a Fluke or similar freq meter?
when i release the switch i get zero hertz zero volts
Is this a field flashing switch, or something that you have rigged up as a field suppply? An external field supply must be constantly present, unless this is a self exciting gen. That is, a gen that "recycles" part of it's armature (load) output back to the excitor for the field voltage, after the initial field has been flashed during start-up. The field strength may change under load (within the rated limits of the gen) if you are externally exciting the gen.

can a winding that checks good for resistance fail when voltage is applied?
Yes, that can happen. What you need to do is check for insulation breakdown, which can not be done properly with an ohm-meter. You need a meggar meter which actually runs a voltage through the windings and measures the resistance of the insulation to the frame (ground) of the gen.

Keep posting and we'll figure this out.

#### rcflier00

Joined Jul 25, 2005
2
Is this a home built generator, or something off the shelf that you're trying to get to work?
i have voltage going to the exciter stator when i energize the gen but i only get low hertz and very low volts. when i release the switch i get zero hertz zero volts

Yes, that can happen. What you need to do is check for insulation breakdown, which can not be done properly with an ohm-meter. You need a meggar meter which actually runs a voltage through the windings and measures the resistance of the insulation to the frame (ground) of the gen.

Keep posting and we'll figure this out.
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Thanx for your reply. this is a 400Hz precise gen with a field flash circuit, and I've got good engine rpm. the power source is an exciter/regulator that operates off of 24v DC, im not sure what the inital voltage should be. why i was thinking it might be the exciter stator, i was only reading 1.9v at the field wire, thinking that it should be more, mabey there was a voltage drop. i pulled the stator and inspected it, found a hot spot on one of the windings. i then checked the resistance an it was 2.4 ohms [1 to 4 allowed] across the field wires. i dont have access to any special tools, except for a fluke meter, wiring diagram, and alot of trial and error.

i've tried known good regulators and circuit protection devices. im measuring 24v at the f1 and f2 wires with the stator disconnected and that checks good with what info i have for the field flash, thats why i was thinking it might be the stator.

i cant be sure that this one worked right before i got it, it came to me in several pieces.