I am working on a generator that should be producing 480/277 Volt 60 Hz 3 Phase power. However it is only producing 400/231 Volt 60 Hz (Yes we tested the frequency to ensure we were not producing 50 Hz) 3 Phase. It is a 12 lead alternator pre-wired from the factory for a series star combination. However one of my coworkers put a jumper across the mid point of all three phases before it was started (thinking he was creating the star point). This jumper has been removed and we now have this voltage problem.

Anyone have any ideas??

 

Some questions:
Was the generator working before or this is the first start up?
What AVR is using?

If this is the first start up, maybe the AVR was pre-configured to control 400V instead 480 as you want. If this is the case, you have to change the reference. Depending the AVR type, this is achieved by mean of software or moving a preset in the front of it.

Regards

 

Greg... presuming the machine is based on US standards, then:

1) Typically a 12-lead generator has 6-windings (or stator coils!) And each coil has 2 termination Tags, i.e., 1-4, 2-5, 3-6, 7-10, 8-11, 9-12!

2) Only one Wye-connection can result in a 4-wire, 480Y/277V output! But it only has ONE mid-point connnection representing the neutral-wire, i.e., 10-11-12!

3) It is not electrically possible in the normal 12-lead machine to obtain a phase-to-phase voltage of 480V, with the phase-neutral being 231V!

4) It would be extremely helpful you could provide answers to Sebastion's important questions!

Regards,
Phil Corso

 

Thanks for your replies. We got it working and you were correct about the AVR being preset to 400V.