3 phase rectifier.

[jotec]

As some will know I run a CHP fueled with WVO.

The system consists of a 3 phase PMA, a 80A bridge rectifier and  Windyboy GTI driven by a Lister CS.

The PMA is driven at about 3000 RPM and outputs 2kW, 300V DC, after the rectifier, at this speed. The temperature of the PMA is around 100C. The diesel maximum output is 3kW.
The 300V DC is fed the Windyboy and into the mains. It has output over 6MW so far.

I now have a problem.
After running for a while, 30 mins?, I am getting a massive load on the generator that it can not cope with and it is slowing down with the governor fully open (lots of black smoke smuts etc!!). Switch of the DC to the grid tie inverter for a short time and it is fine for a time that gets progressively less with each cycle of slowing and removing load. The Lister has been  tested and ruled out as the problem.

I now believe this to be a short somewhere that is effectively putting a brake on the PMA.

Question.
Is this more likely to be the rectifier shorting out as it heats up?
A fault in the windings of the PMA?
I don't think it is the Windyboy as it does not show any faults.

Both test fine when off load but I am not an expert. What readings should I expect from the PMA and rectifier when tested with a multi metre on the bench?

Hope someone can help.

The PMA and rectifier came from the USA so where is the best place to get a rectifier that can cope from in this country,

Thanks
Dick

[Countrypaul]

Could you try a resistive load such as a immersion heater, or electric fire, across the output of the PMA instead of the rectifier. You may need 3 loads since its 3 phase, but it might allow you to eliminate the rectifier and the windyboy. Just an idea as I am by no means experienced in this area.

Paul

[guydewdney]

I have in my grubby mitt a 600v 100A three phase bridge rectumfrier. Its yours if you want it. will post in a jiffy bag.

test a 3 phase rectumfier-
continuity between:-
ac to + side from all three inputs
- to plus (ie red of your multimeter to the - and black to the + should read 0 ohms)

no continuity from + to anything (ie red on + black on anything)


but quite frankly, its more likely to be a shorting wire in the pma im afraid. All the wires shoudl read the same resistance to each other or neutral.

[jotec]

Thanks for that Guy.
I have tested the PMA and cold it is fine with the same resistance to each other, only 3 wires.
I will strip it down tomorrow and see what I can see.
I would like to try another rectifier to rule it out. I will pm my address.