electricpete
Electrical
- May 4, 2001
- 16,774
Our powerplant has a breaker and half scheme in our 345kv switchyard. Our generator feeds 2200A at into one of the bays and splits in two directions through two generator-position breakers.
We have a hotspot identified by thermography on a disconnect for one of the generator position breaker disconnects.
First reading was 64C rise under 7.5mph wind conditions.
Two days later we had only 10C rise under 2.5mph wind conditions (normally expect decreased wind to cause temperature to go up). Thermographic images are here if anyone is interested:
I haven't been able to determine current in these two branches. Power flow through various circuits is monitored with revenue metering but due to deregulation, it is a highly protected secret.
I haven't drawn any conclusions as to the cause of the decrease in temeprature yet. It is possible the connection begins to heal itself or the current has changed either due to other external loading conditions or remotely possible the current has changed due to the resistance of the connection. I rule out the possibility that the OTHER parallel path same phase has a high resistance connection forcing higher current through this phase based on adjacent connection points... this phase is not higher than it's sister phases at the adjacent connection points. Again I am still gathering data and not drawing any conclusions but I have a question:
*** My questions are: how much effect do we effect the resistance of that degraded connection have on the splitting of current through parallel paths. To get to the same point, the two parallel paths have to go perhaps 80 yards distance through the shortest path (with multiple other parallel paths). It is tubular aluminum bus. I am suspecting that the current sharing in a normal circuit would be determined primarily by inductance and resistance would be much lower. If that were true, I wouldn't think the resistance of the hot connection would affect current sharing unless the resistance was extremely high. Any thoughts on this question? What would be the rough X/R ratio of this type of bus? ****
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We have a hotspot identified by thermography on a disconnect for one of the generator position breaker disconnects.
First reading was 64C rise under 7.5mph wind conditions.
Two days later we had only 10C rise under 2.5mph wind conditions (normally expect decreased wind to cause temperature to go up). Thermographic images are here if anyone is interested:
I haven't been able to determine current in these two branches. Power flow through various circuits is monitored with revenue metering but due to deregulation, it is a highly protected secret.
I haven't drawn any conclusions as to the cause of the decrease in temeprature yet. It is possible the connection begins to heal itself or the current has changed either due to other external loading conditions or remotely possible the current has changed due to the resistance of the connection. I rule out the possibility that the OTHER parallel path same phase has a high resistance connection forcing higher current through this phase based on adjacent connection points... this phase is not higher than it's sister phases at the adjacent connection points. Again I am still gathering data and not drawing any conclusions but I have a question:
*** My questions are: how much effect do we effect the resistance of that degraded connection have on the splitting of current through parallel paths. To get to the same point, the two parallel paths have to go perhaps 80 yards distance through the shortest path (with multiple other parallel paths). It is tubular aluminum bus. I am suspecting that the current sharing in a normal circuit would be determined primarily by inductance and resistance would be much lower. If that were true, I wouldn't think the resistance of the hot connection would affect current sharing unless the resistance was extremely high. Any thoughts on this question? What would be the rough X/R ratio of this type of bus? ****
=====================================
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