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Re: Rectifier diode usual shorted circuit.

Sounds like you may have issues with the paralleling setup for this unit. Have you looked at your HZ and voltage windows in the sync section of th woodward controller. If the unit bumps when the breaker closes it would indicate an out of sync condition which could be many things but start with simple stuff like the settings for the synchronizer. Verify the actual sync with a scope or volt meter to verify the synchronizer is doing its job correctly.
New member

Re: Rectifier diode usual shorted circuit.

Hello Everyone;

I got a problem like dr22. I have checked jumper cables. These are good. Only a cable from positive diode to varistor is damaged. I faced burned varistor. I checked windings resistor. They are in good position.

After that the diode's one current path is shorted. Do you have any advise to me
Contributor

Re: Rectifier diode usual shorted circuit.

sorry, i thougth i had told you the trouble was fixed.

there was a bad jumper wire between rectifiers, since i made them new, the trouble was fixed. I'm started asking for complete rectifier gp, but i'm still using crydom M50100THA1600 / C1600 rectifiers. thank you very much for asisting me.

best regards.

Damiàn

New member

Re: Rectifier diode usual shorted circuit.

I want to know that is it the same diode on the same bridge every time? Or is it randomly one of the diodes in a single module?.

Since you are only replacing the diode module I'm assuming you are NOT using CAT parts, as currently only the entire rotating rectifier assembly is available for parts service.

Have you tested it? both a insulation resistance and winding resisitance tests should be done, esppecially if you are seing the same diod fail each time.  

You can try to install the current design rotating rectifier assembly complete.

Contributor

Re: Rectifier diode usual shorted circuit.

already made insulation testing with good results. this time i made a rectifier rotor with older rectifier bridges. i found a damagged jumper between diode bridges and replaced it. working rigth now... i'll share yo the news...

thanks again.

 

Super Contributor

Re: Rectifier diode usual shorted circuit.

Is it the same diode on the same bridge every time? Or is it randomly one of the diodes in a single module?.

 

Since you are only replacing the diode module I'm assuming you are NOT using CAT parts, as currently only the entire rotating rectifier assembly is available for parts service. 

 

A few years ago there was a large number of diode failures that CAT never fully disclosed the root cause, but the result was a change in some of the components and only allowing replacement of the entire rotating rectifier, since that change it appears most fo the didoe problems have gone away.

 

You can try to install the current design rotating rectifier assembly complete.

 

Before you do that I would take a closer look at the rotor and especially the exciter rotor. Have you tested it? both a insulation resistance and winding resisitance tests should be done, esppecially if you are seing the same diod fail each time. Also check the wiring from the exciter rotor to the rotating rectifier assembly, and the jumpers between the diode modules.

 

Hope that helps, MikeL.

Contributor

Re: Rectifier diode usual shorted circuit.

Well...first of all, thanks for your time.
I must always replace the varistor when a shorted diode fails ocurr.there was not any unusual event like you describe, it just happens random time. I did not check pole jumpers, but i will. It's a BPD power module, 3516B, with a 1hz and a 4fn prime gen. Cdvr regulator, emcp II, easygen 3200, Crydom M50100THC1600/THA1600 bridges. Working at 400V 50Hz. 1350Kw. 0,96Pf. No fault logs asociated with the trouble. But i'll check some stuff in a few ours just in case.
The thing is that i usually find only one diode shorted in one bridge, but not the three of them.
Super Contributor

Re: Rectifier diode usual shorted circuit.

In general terms,

 

A shorted diode is usually due to voltage applied being higher than rated.

 

An open diode is usually due to the current being higher than rated.

 

Shorted diodes usually result from an event that causes a higher than expected voltage on the rotor, such as a lightening strike, an out of phase close, an inadvertant energization of a motoring event. I have also seen a rotor with a loose pole jumper cause the diodes to short, rare but happens.

 

When this happens do you replace only the diode or have you also replaced the varistor? Usually if the diode shorts then the varistor if also failed. Is this a CAT generator or another make like a Kato, AVK or Baylor?

 

What kind of voltage regulator do you have?

 

What kind of electrical protective relay? Have you reviewed any event logs from the protection that may indicate the root cause?

 

MikeL.

Contributor
Accepted Solution

Rectifier diode usual shorted circuit.

sorry to border and sorry about my english, it's not my native language, but i'll try you to understand me.

the thing is that i'm a technician in a 20 MW power plant and i have only one 3516B that usually burns a diode rectifier.

got a PMG generator type, with a rectifier rotor plate consisting of an positive three diode rectifier and a negative one, wired to a varistor.

the thing is that usually one of the diodes of a rectifier goes short circuited, but still don't know why.

already made an excitation insulation test, checked excitation voltaje and current, instaled new diode rectifiers with thermal grease, and other stuff...

any clue???

thanks for your time