Specifications

63230-507-201A1 Power Meter 750
03/2007 Appendix C—Instrument Transformer Wiring: Troubleshooting Guide
© 2007 Schneider Electric All Rights Reserved
51
APPENDIX C—INSTRUMENT TRANSFORMER WIRING:
TROUBLESHOOTING GUIDE
Abnormal readings in an installed meter can sometimes signify improper
wiring. This appendix is provided as an aid in troubleshooting potential
wiring problems.
SECTION I: USING THIS GUIDE The following sections contain “Case” tables showing a variety of symptoms
and probable causes. The symptoms listed are “ideal,” and some judgment
should be exercised when troubleshooting. For example, if the kW reading
is 25, but you know that it should be about 300 kW, go to a table where
“kW = 0” is listed as one of the symptoms.
“Section II: Common Problems for 3-Wire and 4-Wire Systems ” addresses
symptoms and possible causes that occur regardless of system type. Check
this section first. If the symptoms are more complicated, proceed to “Section
III: 3-Wire System Troubleshooting” or “Section IV: 4-Wire System
Troubleshooting” as is appropriate.
Because it is nearly impossible to address all combinations of multiple
wiring mistakes or other problems that can occur (e.g., blown PT fuses,
missing PT neutral ground connection, etc.), this guide generally addresses
only one wiring problem at a time.
Before trying to troubleshoot wiring problems, it is imperative that all
instantaneous readings be available for reference. Specifically those
readings should include the following:
• line-to-line voltages
• line-to-neutral voltages
• phase currents
• power factor
• kW
• kVAR
• kVA
What is Normal? Most power systems have a lagging (inductive) power factor. The only time
a leading power factor is expected is if power factor correction capacitors
are switched in or over-excited synchronous motors with enough capacitive
kVARS on-line to overcorrect the power factor to leading. Some
uninterruptable power supplies (UPS) also produce a leading power factor.
"Normal" lagging power system readings are as follows:
• Positive kW =
• Negative kVAR =
• kVA (always positive) =
• = lagging in the range 0.70 to 1.00 (for 4-wire systems, all
phase PFs are about the same)
• Phase currents approximately equal
• Phase voltages approximately equal
3
(
V
AB
× I
3Φ Avg
× PF
3Φ Avg
)× 1000⁄
kVA)
2
kW)
2
(–(()1000⁄
3V
AB
× I
3Φ Avg
×)1000⁄
(
PF
3Φ Avg