Schneider Electric PM850, PM870, PM820, PM810 manual Section II 3-Wire System Troubleshooting

63230-500-225A2			PowerLogicTM Series 800 Power Meter
3/2011			Appendix A—Instrument Transformer Wiring: Troubleshooting Tables
Section II: 3-Wire System Troubleshooting
Section II—Case A
	Symptoms: 3-Wire		Possible Causes
	• Currents and voltages approximately balanced		• CT secondary leads are swapped (A-phase lead on C-phase terminal and
	• kW = near 0		vice versa).
	• kVAR = near 0		• PT secondary leads are swapped (A-phase lead on C-phase terminal and
	• PF can be any value, probably fluctuating		vice versa).
Section II—Case B
	Symptoms: 3-Wire		Possible Causes
	•	Phase B current is 3 higher than A and C
		(except in System Type 31).
	• kVA = about half of the expected magnitude
	• kW and kVAR can be positive or negative, less		• One CT polarity is backwards.
		than about half of the expected magnitude.
	• PF can be any value, probably a low leading
		value.
Section II—Case C
	Symptoms: 3-Wire		Possible Causes
	•	VCA is 3 higher than VAB and VBC
	• kVA = about half of the expected magnitude
	• kW and kVAR can be positive or negative, less		• One PT polarity is backwards.
		than about half of the expected magnitude
	• PF can be any value, probably a low leading
		value
Section II—Case D
	Symptoms: 3-Wire		Possible Causes
	• kW = 0 or low, with magnitude less than kVAR		• Either the two voltage leads are swapped OR the two current leads are
	• kVAR = positive or negative with magnitude of		swapped AND one instrument transformer has backwards polarity.
		close to what is expected for kW	(look for VCA= 3 high or phase B current = 3 high)
	• kVA = expected magnitude		• The power meter is metering a purely capacitive load (this is unusual); in
	• PF = near 0 up to about 0.7 lead		this case kW and kVAR will be positive and PF will be near 0 lead.

Section II—Case E

Symptoms: 3-Wire Possible Causes

•One phase current reads 0

•The CT on the phase that reads 0 is short-circuited.

•kVA = about 1/2 of the expected value

•Less than 2% current (based on CT ratio) flowing through the CT on the

	• kW, kVAR, and power factor can be positive or	phase that reads 0.
	negative of any value
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