Specifications

Power Meter 750 63230-507-201A1

Appendix C—Instrument Transformer Wiring: Troubleshooting Guide 03/2007

A quick check for proper readings consists of kW comparisons (calculated

using the equation above 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.

SECTION II: COMMON PROBLEMS FOR

3-WIRE AND 4-WIRE SYSTEMS

SECTION III: 3-WIRE SYSTEM

TROUBLESHOOTING

Table C– 1: Section II—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”

Table C– 2: Section II—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.

Table C– 3: Section II—Case C

Symptoms: 3-Wire and 4-Wire Possible Causes

• Frequency is an abnormal value; may or may not be a

multiple of 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

Table C– 4: Section III—Case A

Symptoms: 3-Wire Possible Causes

• Currents and voltages approximately balanced

• kW = near 0

• kVAR = near 0

• PF can be any value, probably fluctuating

• CT secondary leads are swapped (A-phase lead on C-phase terminal and

vice versa)

• PT secondary leads are swapped (A-phase lead on C-phase terminal and

vice versa)