Schneider Electric PM820, PM870, PM810, PM850 manual Using This Appendix, What is Normal?

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

Appendix A—Instrument Transformer Wiring: Troubleshooting Tables

Using This Appendix

What is Normal?

Abnormal readings in an installed meter can sometimes signify improper wiring. This appendix is provided as an aid in troubleshooting potential wiring problems.

The following pages contain “Case” tables arranged in sections. These tables show a variety of symptoms and probable causes.

Section I: Check these tables first. These are common problems for 3-wire and 4-wire systems that can occur regardless of system type.

Section II: Check these tables if troubleshooting more complex 3-wire systems.

Section III: Check these tables if troubleshooting more complex 4-wire systems.

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.

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), 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

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 are 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 = ( 3 × VAB × I3ΦAvg × PF3ΦAvg ) ⁄ 1000

•Negative kVAR = ( (kVA )2 – (kW )2 ) ⁄ 1000

•kVA (always positive) = ( 3 × VAB × I3ΦAvg ) ⁄ 1000

•PF3ΦAvg = 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

A quick check for proper readings consists of kW comparisons (calculated using the previous equation and compared to the meter reading) and a reasonable lagging 3-phase average power factor reading. If these checks are okay, there is little reason to continue to check for wiring problems.

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