Needing help troubleshooting voltage loss through entire saw mill

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wyopokesfan

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Saratoga, WY, USA
I recently noticed we had a drop in voltage across the entire saw mill where I work. Am relatively new here but think the loaded voltage here was close to 480V. Contacted a former electrician here and he agreed. We are fed from one feed of the power company to two 2500KVA transformers. One part of our facility coming off of transformer 1 is normal voltage, 480-482V loaded. Every MCC in the mill coming off of transformer 2 is 458-462Vphase to phase, loaded (running full production). The voltage coming out of the transformer is only 467 phase to phase loaded. All phases are withing a couple volts of each other and also within a couple volts all three phases to neutral (264-267V). Went through every MCC this morning on the main breakers and every large motor with 3 amp clamps, no real current imbalance or voltage imbalance anywhere. Could something in the mill be drawing the voltage down? Or possibly the transformer going bad? I know I can re-tap the transformer to get more out of it, but that does not explain the loss. I do not have CT's big enough to go around all 12 paralleled conductors on each phase coming from transformer. Also do not know of any metering devices in the mill to show me what the incoming voltage, current, etc. are. Any ideas would be greatly appreciated. Since I noticed the drop, we have had numerous 480V circuit breakers trip in random locations throughout the mill.
 
Can the voltage be checked without load? The voltage would vary as loads change if voltage drop is the problem.
 
wyopokesfan said:
With the lights in the mill being almost the only load yesterday morning before we started up, there was 477V at all of the MCC's and 480V coming from the transformer.
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voltage drop
what is current off each xfmr
what is the load current off each
pu z for each
feeder length and size

xfmr no load to full load drop = 480-467 = 13 or 2.7%
xfmr to mcc drop full load = 467-460 = 7 or 1.5%
xfmr to mcc drop no load = 480-477 = 3 or 0.6%
mcc no load to full load drop = 477-460 = 17 or 3.6%
xfmr to mcc no load to full load drop = 480-460 = 20 or 4.2%

looks like xfmr is 65% of the drop
increase a tap
 
wyopokesfan said:
I recently noticed we had a drop in voltage across the entire saw mill where I work. Am relatively new here but think the loaded voltage here was close to 480V. Contacted a former electrician here and he agreed. We are fed from one feed of the power company to two 2500KVA transformers. One part of our facility coming off of transformer 1 is normal voltage, 480-482V loaded. Every MCC in the mill coming off of transformer 2 is 458-462Vphase to phase, loaded (running full production). The voltage coming out of the transformer is only 467 phase to phase loaded. All phases are withing a couple volts of each other and also within a couple volts all three phases to neutral (264-267V). Went through every MCC this morning on the main breakers and every large motor with 3 amp clamps, no real current imbalance or voltage imbalance anywhere. Could something in the mill be drawing the voltage down? Or possibly the transformer going bad? I know I can re-tap the transformer to get more out of it, but that does not explain the loss. I do not have CT's big enough to go around all 12 paralleled conductors on each phase coming from transformer. Also do not know of any metering devices in the mill to show me what the incoming voltage, current, etc. are. Any ideas would be greatly appreciated. Since I noticed the drop, we have had numerous 480V circuit breakers trip in random locations throughout the mill.
Click to expand...
Since both transformers are same rating you can expect both to put out nearly same unloaded voltage. You did not say what total load on each one is though, you also did not say if both have same size, type, length of conductors. Different load level and different conductor resistance due to size or length can easily contribute to the differences you are seeing.
 
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