Specifications

Power Meter 750 63230-507-201A1
Appendix C—Instrument Transformer Wiring: Troubleshooting Guide 03/2007
© 2007 Schneider Electric All Rights Reserved56
FIELD EXAMPLE Readings from a 4-wire system
•
•
•
•
•
•
•
•
•
•
•
•
•
•
lag to 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 =
=
=
• 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
kW 25=
kVAR 15–=
kVA 27=
I
A
904A=
I
B
910A=
I
C
931A=
I
3Φ Avg
908A=
V
AB
495V=
V
BC
491V=
V
CA
491V=
V
AN
287V=
V
BN
287V=
V
CN
284V=
PF
3Φ Avg
0.75= 0.22
3V
ab
× I
3ΦAvg
×)1000⁄(
1.732 495 908 ) 1000⁄××(
778 kVA