Harmonics on three systems

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aelectricalman

aelectricalman

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Location
KY
I was not able to measure harmonic orders and harmonic Vthd for three services at the PCC but I was able to measure them at each respective gear. I went in initially thinking that the customer had parallel resonance on one for their cap banks contributing to some overheating issues and breaker tripping. What I found was that all three services (each fed by a different 3000kVA transformer from the utility) had the exact same Vthd (5.67%) and 5th order harmonics (5.37%) during the same time frame. The three services are fed from the same circuit as many other businesses are and this customer is the first customer on the circuit.

Each transformer represents completely different functions and there are no two pieces of like equipment on either of the three service. Do you think it is safe to say that these are harmonics from the utility line (from somewhere else)? I would have expected one service to be higher than the other two.

My logic is that if there were a parallel resonance on one service, it would have to resonate back through the utility feed (from 480V up to 13.2 kV) and come back in on the other services. In that case, all three would not be equal. Since they are fed from the same source, and all three harmonic %'s are equal, they must resonate from the same place (utility feed).

Thanks for any input .
 
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