Filter
Top Products
PowerLogic
TM
Series 800 Power Meter 63230-500-225A2
Appendix A—Instrument Transformer Wiring: Troubleshooting Tables 3/2011
© 2011 Schneider Electric All Rights Reserved
74
Section I: Common Problems for 3-Wire and 4-Wire Systems
Section I—Case A
Symptoms: 3-Wire and 4-Wire Possible Causes
• Zero amps
• Zero kW, kVAR, kVA
• CT secondaries shorted.
• Less than 2% load on power meter based on CT ratio.
Example: with 100/5 CT's, at least 2A must flow through CT window for power
meter to “wake up.”
Section I—Case B
Symptoms: 3-Wire and 4-Wire Possible Causes
• Negative kW of expected magnitude
• Positive kVAR
• Normal lagging power factor
• All three CT polarities backwards; could be CTs are physically mounted
with primary polarity mark toward the load instead of toward source or
secondary leads swapped.
• All three PT polarities backwards; again, could be on primary or secondary.
NOTE: Experience shows CTs are usually the problem.
Section I—Case C
Symptoms: 3-Wire and 4-Wire Possible Causes
• Frequency is an abnormal value; may or may
not be a multiple of 50/60 Hz.
• PTs primary and/or secondary neutral common not grounded (values as
high as 275 Hz and as low as 10 Hz have been seen).
• System grounding problem at the power distribution transformer (such as
utility transformer), though this is not likely.