The Work Of An Exciter

Well I'm not sure what you mean by an exciter. In the cases that I know of with an alternator the exciter current connects to the rotor windings and not the stator windings. Modulating this current allows controlled regulation of the stator output voltage. Now many alternators source their rotor current from the stator output voltage. This begs the question how current anywhere in this tail chase design ever initially starts to flow in the first place, because at first no stator current exists to make a magnetic field to generate a stator voltage. The only thing that exists is the energy from the prime mover that spins the rotor. Well the trick here is that the magnetic field magnitude from the rotor is not really zero when no current flows through the rotor windings. The natural hysteresis of the iron core produces a small non-zero magnetic field with no rotor winding current. So some of the energy from the prime mover can still be converted to electrical energy at the stator to now drive more current into the rotor.

I suspect that the OP has such a self exciting alternator and is just confusing the roles in this scenario that resembles a dog chasing its own tail.

Or he may have a regular brushless exciter and exciting it with something like a Basler VR and doesn't see why the DC from the VR has to be rectified again.

Because the DC Voltage from your VR is transferred without brushes to the rotating stator (or armature) it is turned into AC at the rotating coils of the Exciter Ring, the diodes turn that AC back into DC for the coils of the Stator.

In KISS:

· You feed your generator DC from the Voltage regulator

· That DC makes a field the rotating coils, on the exciter ring, cut and induce AC

· The Diodes turn that new AC back to DC for the Generator Rotating Field

· The varistor's are MOV's that short out voltage spikes. if thay are shorted they are bad, if that are burned same thing but exciter will work.

Look out for shorted/opened diodes too, if they are opened it will look like they are OK with an ohm meter because you'll read forward bias through the other diode, you have to disconnect them to test unless you keep the reverse/forward bias straight in your head and half the diodes will anode to the tail and the other half will be cathode to the tail.

Good post on the tail chasing of a self excited AVR redfred,

Revert to the comments you received in your previous question "The Principle Of Operation Of The PMG To The Exciter To Then The Stator" which explains the whole chain from the PMG to the Main Field.

Ya, i saw that after 20 min's on this post, think he miss spelled his name. Maybe someone else will be helped on troubleshooting exciter diodes, it's good and learned over many years, when i get called out on unstable voltage, and the VR has been changed, the diodes are usually it because the Electrician didn't disconnect them when checking. if it doesn't make full voltage, even when flashed, it's one of the MOV's failed shorted and not destroyed because of the low amps in the exciter ring.

Pearls Before Swine for this OP

Dear Bongus,

Refer link:

The-Principle-Of-Operation-Of-The-PMG-To-The-Exciter-To-Then-The-Stator

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