DC drive sudden high bridge temp

[Thedroid]

2 different drives are experiencing higher than normal bridge temps after a 6 month shutdown. Both are ABB DCS 500's. One is for a 40 hp motor, the other is for 2 75hp with the armatures in series. They are both way under FLA. Before the shutdown these drives both had bridge temps under 30C. Within hours of startup we were seeing temps around 60C. We're using portable ac units right now to keep the temps down to around 35, but would like to remove them at some point. Both drives are supplied by the same 4160/480 delta/wye and they each have their own 480/480 delt/wye isolation transformers. Voltage measurements are 485 l-l and 295 320 295 l-g off the isolation transformer, and normal before it. Is there a common component that may be failing from sitting too long?

 

[itsmoked]

I'm not seeing a problem with 60C...

You can de-power it all and re-check any mounting fasteners. That's likely the only thing that changed in months. If something had failed I'd expect you'd be seeing other symptom.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[sibeen]

Thedroid, from the L-g voltages you've posted it appears that you have a bit of a voltage imbalance.

Have you looked at the incoming current, both in magnitude and harmonic content?

 

[Thedroid]

I agree that 60C is not out of bounds. My concern stems from the fact that these drives historically stayed below 30C for years. Voltage and current appear normal on the line side of the isolation transformer, on the drive side is where I took the stange readings posted. I'm assuming that there is some harmonics going on, and it might be causing the heating. I just find it strange that both drives are behaving differently. They are on the same line but located several hundred feet away in clean cool environments.

 

[ScottyUK]

Chances are the low phase is upsetting the current distribution and some of the rectifiers are doing far more than their share of the work. That might explain the high heatsink temperature. It would certainly result in the individual diodes being hotter than they would be with a balanced supply.


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If we learn from our mistakes I'm getting a great education!

 

[DickDV]

First, I'd say that 60 degrees C is not a problem. These drives will alarm and then fault if too hot.

Second, I can't imagine the drives supplying any significant energy to the motor and remaining at 30 degrees C. Shucks, in most cases the ambient is that hot. Either something is wrong with the 30 degree C figure or the motors weren't doing any work before and are doing a little more now.

I don't think you have a problem.

 

[Thedroid]

The maximum bridge temp is 95C, so no 60 is not too hot. The motors and drives are bothe oversized in order to provide overload capacity. The load has not changed, and neither has the current required. These drives are for a grate clinker cooler, and a cement kiln. There are identical drives right next to these units which still run under 30C. Both areas a cooled, and ambient rarely exceeds 21C. The larger drives have cabinet coolers also.

As far as work being done, the 40hp unit fluctuates between 6-14A with plenty of reserve in case of trouble, and the series wired 75's average around 80-120A. Loads between both kiln lines are very close, as was the temperature before the shutdown. We check bridge temp on our daily walk arounds. Keeping the temp down is important for us. ABB advised us that the drives would last multiples of years longer if we could keep the bridge temp under 35.

 

[ScottyUK]

The components you're protecting are mainly the electrolytic capacitors on the DC link. They will be the first to significantly age. In some drives they aren't too bad to replace, others are the devil's own work. Smaller drives tend to use small PCB-mounted caps, and those are usually the awkward ones.


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If we learn from our mistakes I'm getting a great education!

 

[Skogsgurra]

DCS not ACS.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScottyUK]

Thanks skogs.


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If we learn from our mistakes I'm getting a great education!