Schneider Electric PM810 Field Example, Readings from a 4-wire system, Troubleshooting Diagnosis

PowerLogicTM Series 800 Power Meter	63230-500-225A2
Appendix A—Instrument Transformer Wiring: Troubleshooting Tables	3/2011

Field Example

Readings from a 4-wire system

•kW= 25

•kVAR= –15

•kVA= 27

•IA= 904A

•IB= 910A

•IC= 931A

•I3ΦAvg= 908A

•VAB= 495V

•VBC= 491V

•VCA= 491V

•VAN= 287V

•VBN= 287V

•VCN= 284V

•PF3ΦAvg= 0.75 lag to 0.22 lead fluctuating

Troubleshooting Diagnosis

•Power factors cannot be correct .

•None of the “Section II” symptoms exist, so proceed to the 4-wire troubleshooting (“Section IV”).

•Cannot calculate kW because 3-phase power factor cannot be right, so calculate kVA instead.

•Calculated kVA = ( 3 × Vab × I3ΦAvg ) ⁄ 1000

=(1.732 × 495 × 908 ) ⁄ 1000

=778 kVA

•Power meter reading is essentially zero compared to this value.

•4-wire Case E looks similar.

•Since the PTs were connected to other power meters which were reading correctly, suspect two CT leads swapped.

•Since A-phase power factor is the only one that has a normal looking lagging value, suspect B and C-phase CT leads may be swapped.

•After swapping B and C-phase CT leads, all readings went to the expected values; problem solved.

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