Snubber brake on Reliance VFD

[Carl Cadieux]

I believe you are right with the unit chosen (2ST40075). I just need to find the time to get a look at inside the brake unit. Bare with me.

 

[Carl Cadieux]

What is Bonitron, a model of brake? I already have a spare dynamic brake that was on a 30 HP motor/drive.

 

[kamenges]

Bonitron in the post is a link. Click on it.

One of the products Bonitron makes is a line regen module that connects to a drives braking terminals. It puts the energy back on the AC line.

Keith

 

[kamenges]

I don't know how you feel about such things, but as luck would have it...

http://cgi.ebay.com/Bonitron-M3345-...179?pt=LH_DefaultDomain_0&hash=item3ef825b943

Keith

 

[Carl Cadieux]

I have had experience with regen units and it wasn't good. Too many problems with VFD's blowing. I replaced the regen brake with a dynamic and never had a problem after. Thanks anyway.

 

[kamenges]

Interesting. I've used several of these and never had any issues. Were they Bonitron and Reliance combinations or someone else (just so I know who to steer clear of)?

Keith

 

[DickDV]

Carl C. Please don't interpret my comments as meaning that you can't put a 20hp brake on a 30hp drive. You surely can.

You will be limited in braking capacity by the chopper rating. But, if 20hp of braking will stop your machine in an acceptable time, then you can use the existing hardware. But, it seems that that hardware isn't working at all.

To maximize the capacity of the 20hp brake, you must find the minimum acceptable resistance value for it and provide that resistance. As to the wattage, since you've got a 20hp brake, the maximum resistor wattage would be the 15kw I mentioned above. If the duty cycle is lower, you can get away with less wattage down to one-tenth of the above rating for an occasional stop with completely cold resistors and no repeat until the resistors are fully cooled again. From what you describe with the centrifuge, 12-15kw may be required.

Remember that the drive software must permit the DC bus to ride up high enough to activate the chopper. In the software somewhere is a parameter that alters the decel ramp to avoid a HV trip. This feature must be turned off for the chopper to work.

Otherwise, you've got hardware problems. If, on stopping, any voltage at all appears across the resistors, its not an internal fuse. I'd check the DC bus under braking conditions to be sure it rises above 780 volts. If it does and the chopper is still not putting out any voltage to the resistors, the chopper is bad.

 

[Carl Cadieux]

No, It was a combination Siemens 30 hp drive and regen brake. One thing to keep in mind is that our power is not great which doesn't help. It even had a reactor on the incoming which should have helped but no go. This particular unit is moth balled now so we now have a spare dynamic brake (that replaced the regen unit)that I am trying to use.

 

[Honga]

FYI resistors work by turning electrical energy into thermal energy.

If you add more resistors in the same space you simply have the same thermal output, only a larger area of dissipation. This will not help unless well ventilated.

 

[DickDV]

Well, Carl, it seems that I've gotten confused. I'm now not clear on what you have or even what you want to acheive. And now you throw in power quality issues and its not Reliance but Siemens.

When you are ready to lay out in detail what your problem is and what you want to accomplish, post it and I, for one, will be happy to help.

Lacking that, I'm done. I can't hit a moving target.

 

[Carl Cadieux]

Sorry for the confusion. I was just making the point that the regen brakes come with other problems which can be caused by dirty power.
I will let you know what the outcome is when I get into troubleshooting the Reliance snubber brake.

 

[kamenges]

Dick, Carl's last response was to MY question, not the resistor question. his current implementation is using a braking chopper connected to a Reliance drive.

Keith