140KW Generator-Mystery Diodes

[Richard D]

I don't have any information on this old generator, it's powered by a 6-71 Detroit. Need new diodes, the local electronics supply couldn't tell me what I need. The Varistor seems common enough.

 

[HeadsUp]

Quick search shows the part is obsolete.

https://www.mouser.com/ProductDetail/Littelfuse/V320PA40A?qs=slssyL07VvOgQZV6UJvjXw%3D%3D

Unfortunately I could not easily find a substitute.

 

[RPH]

Look for stud mounted. We used them in the induction generators. They do have both common anode or cathode. Check your old ones first for conduction. The won’t survive the exchange.

 

[Richard D]

It's not the red part I'm looking for, I need the diodes.

 

[CJ7VFR]

The parts that RPH has shown appear to be the correct diodes/rectifiers, or at least damn close to them.

Jim

 

[Richard D]

I will show this to the generator mechanic, thanks!

P.S. Yes I do need the red part as well, and although it is discontinued, I have found NOS units online

 

[Richard D]

Mr. RPH, can you give me a link to that page please?

 

[RPH]

This should get you close. Any numbers you can get will help off the original. When in doubt get the higher rated device.

https://www.mouser.com/Semiconductors/Discrete-Semiconductors/Diodes-Rectifiers/Diodes-General-Purpose-Power-Switching/_/N-ax1mp?P=1z0y2h5Z1yzkpo4&Keyword=diode&FS=True

 

[Richard D]

O.K. thanks, I will pass this on to him, electrical stuff for me is just a magic way to make smoke and sparks where they are not desirable...

 

[RPH]

Another from digi key

Discrete Semiconductor Products | Diodes - Rectifiers - Single | DigiKey

Discrete Semiconductor Products - Diodes - Rectifiers - Single are in stock at Digikey. Order Now! Discrete Semiconductor Products ship same day

www.digikey.com

 

[Lightning rod]

if you are still looking for the varistor, this will work electrically
please check dimensions for your application in the "download datasheet" link

https://www.alliedelec.com/product/hvca/z320pa40a/70016085/

Are you able to post the generator nameplate rating? Just curious as to voltage , 1ph or 3ph etc
thanks

 

[BillK]

Take one out and lightly glass bead it. I bet there is a number on it somewhere.

 

[MBfreak]

There are two identical sets of diodes. One set with cathode to the body/threaded part and one set with anode to the common threaded part.

As long as you replace with modern diodes of the same or bigger physical size and rated for 400 V you will be OK.

As long as you can find ONE healthy diode and let a sparky determine anode or cathode to body/thread you will be OK.
All you need is a simple DVM with diode measuring setting and maybe you can even find a tutorioal on u-tube?
VDR was common in the old days , since peak voltage could destroy the diodes. With modern diodes, I believe you can remove th VDR.

Good luck

Ola

 

[RPH]

There are two identical sets of diodes. One set with cathode to the body/threaded part and one set with anode to the common threaded part.

As long as you replace with modern diodes of the same or bigger physical size and rated for 400 V you will be OK.

As long as you can find ONE healthy diode and let a sparky determine anode or cathode to body/thread you will be OK.
All you need is a simple DVM with diode measuring setting and maybe you can even find a tutorioal on u-tube?
VDR was common in the old days , since peak voltage could destroy the diodes. With modern diodes, I believe you can remove th VDR.

Good luck

Ola

Nice to see you chime in here. Yes, the varistors do have a habit of going bang. We removed them from the smaller induction units due to the 480 vac going high. At Europe’s 400 vac service it worked but you are correct that it’s not absolutely required. Typically if the varistor is in one piece and no char marks around the area we trusted them to be good. Ours always obliterated themselves and left the big carbon mark.

 

[MBfreak]

RPH.
Thanks.
From what I think I can see, the varistor sits between + and - on the output from the 6 diode- three phase- full wave bridge rectifier magnetizing winding that feeds the field in the main generator?
Ola

 

[RPH]

RPH.
Thanks.
From what I think I can see, the varistor sits between + and - on the output from the 6 diode- three phase- full wave bridge rectifier magnetizing winding that feeds the field in the main generator?
Ola

You are correct on the varistor and diodes from what I can see. I’d like to see the complete unit. Gets boring now that I’m retired. I miss the big power and problems it presented.

 

[MBfreak]

Me too, retired from large electrical power system engineering at the early age of 75!
Biggest generators I made system calculations for was 1667 MVA units at two upgraded nuclear power stations.
Excitation there was 1,3 kV and att max 9500 A.
Output voltage 25,2 kV FLA 38500 A. Worst short circuit power 965 kA.
The most demanding and time consuming calculation was the subsynchronuos stability.


Try to keep my brain in order by repairing old car radios!

Ola

 

[RPH]

Company I worked for was based in Skien, Norway. Loved going over for training. I could live over there. My kind of forests.

 

[MBfreak]

The pics from the OP shows serious corrosion damage to several different metals in the rectifier assembly.
I think the OP needs to inspect the entire generator for corrosion on all metal parts and find out the root cause of the corrosion and remedy that.
Ola