I think it all boils down to your intended appication. If you use DELTA-delta, I see no concern as long as it is what you need, and have considered other factors such as need for grounding. However, if this is a utility serving common customer loads, then, a DELTA-wye is the typical connection...
Nah.. In our case, it's already difficult to coordinate more than 4 reclosers. And that's where sectionalizers come in.
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That's interesting. Anyway, if ever you encounter a coordination problem, I think you can consider using sectionalizers depending on the intended application.
Relatively longer to satisfy necessary CTI, but should not exceed the time as per damage curve of protected device. Consequently, if there are too many, it will be impractical to achieve coordination. But as to the limit, I haven't read any standard and you can install as many as you want but...
Yes, it should be fine to energize an unloaded transformer with delta primary as long as you use 3-phase, 3-pole circuit breakers.
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Guys,
Aside from possible wiring mistakes, we're also looking at CT remanence as the possible cause - since it affects CT performance during high current such as load switching and reduces CT accuracy (e.g. ratio) even at steady-state.
Kindly share your experiences...
Thanks...
stevenal,
I apologize for the confusion...
The circuits summed involve two feeder and the main line. Actually, there are four feeders in total but at that time we only loaded two feeders.
Main Line - 200 A
Problem Feeder - 70 A
Adjacent Feeder - 130 A
Other 2 Feeders - No Load (Breakers Open)...
stevenal,
I apologize for the confusion...
The circuits summed involve two feeder and the main line. Actually, there are four feeders in total but at that time we only loaded two feeders.
Main Line - 200 A
Problem Feeder - 70 A
Adjacent Feeder - 130 A
Other 2 Feeders - No Load (Breakers Open)...
Cranky,
The settings were calculated based on SEL guidelines. The 68 V trip setting have a time delay of 1.25 cyc to compensate arrester operation and/or CT unbalance during high current (inrush or external fault). Since you can set two 87 stages, the SEL guideline also recommends to set the...
stevenal,
There were only two feeders up, the one with the problem (70 A) and the adjacent line (130 A)...
Anyway, I'd appreciate to see your calculations for the differential current in case of a phase swap...
Thanks...
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stevenal,
The trip occurred when we first load that feeder... When we tried loading the adjacent feeder, it was successful. So what we did was lengthen the delay to around 5 seconds, and load back the feeder that caused the trip. There was no trip but the relay recorded that the high impedance...
DTR,
Yes, PCIT and secondary loop tests were performed to check the phasing and metering accuracy of the relay...
When you say bonding jumpers, are you referring to the cable shield wires?
Thanks...
stevenal and dpc,
As what I've replied to Eletest, it would seem at first that it is simply a polarity problem (A & C interchanged). However, I'd like to add that aside from the high impedance element voltages, the steady-state differential currents are relatively low: IA = 5-7, IB = 1, IC =...
