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

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

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

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.

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

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

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

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

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

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

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

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

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

LOCKS HELP USE SOME TYPE OF METER BASE LOCKING DEVICES

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

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

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

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?

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

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

QUESTIONS ?