sbubbers

[richerdick32]

Hi
Am I correct in saying that the snubber circuits on the power transistors of an AC drive help to prevent undesired switching of the power transitors. we have a fault and I am considering whether it is worth changing the snubber modules?

 

[Skogsgurra]

You can easily test them. If they are RC snubbers, no sweat. If they are more complex, you may need to think a little. My experience is that gate drive circuits fail a lot more often than snubbers. What make and size of drive is it? What messages do you get?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[mikekilroy]

I would say you are not correct.

Snubber networks around SCRs in drives do help prevent improper firing, but I believe all snubbers around transistor drives are for switching noise/ringing reduction.

http://www.KilroyWasHere<dot>com

 

[itsmoked]

Mike: That ringing can cause the switches to operate on dVdT alone with disastrous results.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[richerdick32]

Thanks for the replies,
Please forgive my descriptions below if they sound a little unprofessional
So this issue we have is on a generator system, I belive the type of generator is an asynchronous generator, the power electronics on the rotor side of the generator from what i can gather convert ac to dc then chop up the dc to create a variable frequency ac on the the rotor ( so basically just like an inverter drive ) which allows the generator to generate at various rotor speeds by compensating adjusting the frequency of the rotor.
The when on load the system switches in two small banks of capacitors which have inductors wired in series i can only guess this is to compensate for harmmonics generated by the Power electronics. The issue we have is that the fuses supplying the capacitors keep blowing intermittantly it is always the center fuse on both banks . the capacitor banks are connected in parallel to the "drive" supply and connected via contactors.
after trying all the simple things, capacitors, contactors etc , i started to think it may be harmonics as there is nothing really on the capacitor circuit other than the capacitors that could draw the current to blow the fuses?
we changed the harmonic filter but still blew fuses again a few weeks later. I was thinking maybe next changing the power transistors on the grid side of the in verter that connected to the center fuses that keep blowing? any thoughts

 

[mls1]

First, your generator as you describe it is a doubly fed induction generator. The inductors wired in series with the capacitors are likely more for reducing back-to-back switching transients rather than for harmonics since your are switching them in close proximity. Have you put any data recorders on the capacitor banks to capture the switching transients and harmonic profiles?

 

[richerdick32]

No unfortunately I think that is a little beyond my capabilities I kind of understand what Harmonics are but that is about the limit of my abilities. This cannot be a design error as it is one of many and the others aren't doing it just running out of ideas and not getting support we need from the people who should be dealing with it.