1. Field Problems with Instrument Transformer Installations
ElectriCities of North Carolina
Advanced Meter School
James Whitaker
Greenville Utilities Commission
Mark Wells
Town of Tarboro

2. Current Transformers
Proportionally steps down the current level in the meter circuit
Isolates meter personnel and metering equipment from high current flow

3. FORM 9S WIRING DIAGRAM USING ONLY CTS
SOME UTILITIES MAY USE ONLY CTS AND NO VTS
THIS IS BY PREFERENCE OR POLICY
THE BILLING MULTIPLIER WILL BE DETERMINED BY THE CT RATIO

4. Voltage Transformers
A voltage transformer or VT steps down higher voltage by some ratio to a level that is safer and more practical to meter.

5. FORM 9S WIRING DIAGRAM USING VTS & CTS
THIS DIAGRAM USES SECONDARY VTs TO STEP DOWN THE VOLTAGE TO 120V
CTs ARE ALSO USED
THE BILLING MULTIPLIER WILL BE A COMBINATION OF VT AND CT RATIO

6. CT PROBLEMS CT POSITIONED BACKWARDS ON PRIMARY CONDUCTOR
THE METER WILL RUN BACKWARDS ON THIS PHASE

7. ANOTHER CT PROBLEM WIRING REVERSED AT SECONDARY SIDE OF CT
SAME EFFECT AS THE PREVIOUS SLIDE, REVERSE ROTATION ON THIS PHASE

8. CT IMPROPER WIRING POLARITY REVERSED
TEST SWITCH CONNECTIONS
SAME THING, REVERSE ROTATION ON THIS PHASE

9. CT INSTALLATION ISSUES
CT SHORTING BAR LEFT IN THE CLOSED POSITION
NO MEASURERMENT OF CURRENT ON THIS PHASE

10. LOOSE SCREW ?
CT CIRCUIT SHORTED
NO OR LOW USAGE ON THIS PHASE

11. OPEN CT CIRCUIT BROKEN OR BURNED CT WIRING
BROKEN NEUTRAL CAN RESULT IN NO REGISTRATION AT ALL
AGAIN, NO MEASUREMENT ON THAT PARTICULIAR PHASE
POSSIBLE DAMAGE TO CT

12. OPEN VOLTAGE CIRCUIT BROKEN VOLTAGE WIRING BAD VT = NO VOLTAGE
NO MEASUREMENT ON THIS PHASE

13. POSSIBLE TAMPERING OPEN TEST SWITCHES ON CURRENT OR VOLTAGE SIDE
NO MEASUREMENT OF CURRENT ON THESE TWO PHASES

14. LOCKS HELP
USE SOME TYPE OF METER BASE LOCKING DEVICES

15. BILLING PROBLEMS BILLING MULTIPLIER CT RATIO 200:5=40
VT RATIO 288:120=2.4
40 X 2.4 = 96

16. WHAT IF ?
INSTALLATION CREW GIVES INCORRECT INFORMATION TO THE BILLING DEPARTMENT
SERVICE UPGRADE, CTS ARE CHANGED TO A HIGHER RATIO AND THE CHANGE NEVER GETS TO THE BILLING DEPARTMENT
BILLING MULTIPLIER IS WRONG!! LOSS OF REVENUE

17. NEW MULTIPLIER SERVICE AND CT UPGRADE
PREVIOUS BILLING MULTIPLIER WAS 96 (40X2.4=96)
NEW CTS 600:5 USING THE SAME VTS WHAT IS THE NEW MULTIPLIER?
600:5=120 X 288:120=2.4 (120 X 2.4=288)
NEW BILLING MULTIPLIER IS 288

18. LOSS OF REVENUE
ALL OF THESE EXAMPLES AND MANY OTHER PROBLEMS CAUSE A TREMENDOUS AMOUNT IN REVENUE LOSS EACH YEAR
WHAT CAN YOU DO TO CORRECT THIS PROBLEM?

19. CT TEST PROGRAM
CHECK NEW INSTALLATIONS AS WELL AS ANY UPGRADES AS THEY ARE DONE. THIS IS WHEN A LOT OF ERRORS OCCUR AND THEY ARE HARD TO CATCH BECAUSE THERE IS NO BILLING HISTORY
HAVE A TEST SCHEDULE TO RECHECK CT INSTALLATIONS PERIODICALLY

20. SAMPLE FIELD TEST WIRE VERIFICATION CT RATIO AND ACCURACY
METER ACCURACY
TOTAL SYSTEM ACCURACY

21. QUESTIONS ?