Watt-Hour Meter Test

MAINTENANCE AND TESTING PROCEDURE• Recommended maintenance and testing procedure will vary considerably among

the various meter designs.

• The manufacturer’s Instruction Leaflets for each design should always be consulted when establishing a maintenance and testing procedure.

• However, the principle of Watt consists of applying current and voltage to both a Rotating Standard Meter and the Meter Under Test, observing the revolutions of both and calculation accuracy by the following formula:

% Meter Accuracy =

Watt-hour Meter Adjustments

SIMPLE RULES FOR CHECKING METER INSTALLATIONS

(1) Check installation against All-In-One diagram.(a) Pay particular attention to voltage and current polarities.(2) Check meter against known load, using formula:

Revs/sec = MKh 3600 / Watts load (Use watch with second hand)

(3) Check line currents. On balanced loads, line currents will be approximately the same for all phases.(4) 3-PHASE, 3 WIRE(a) Interchange two voltage leads on line side. Meter should stop on balanced loads regardless of Power Factor.(b) Open common potential. On balanced loads, meter should run at half speed.

(5) 3-PHASE, 4-WIRE (Y) (2-STATOR OR “Z”)(a) Interchange two voltage leads on line side. Meter should stop on balanced loads

regardless of Power Factor.(b) Open common potential. On balanced loads, meter should run at half speed.

(6) 3-PHASE, 4-WIRE DELTA (2-STATOR)(a) Check one element at a time. On balanced loads, speed should be the same for each

element regardless of Power Factor.

(7) NETWORK(a) Interchange two voltage leads on line side. Meter should run backwards.(b) Check one element at a time. Meter should run at same speed on balanced load,

regardless of Power Factor.

INSPECTION AND CLEANING1. Open the cover and perform Visual Inspection, Cleaning and Maintenance of D4S meter in accordance to RMS-5000-01-I, “Initial Inspection and Cleaning of Metering, Relaying and Communication Equipment”.Is there any dust accumulated inside the meter? Yes: ____ No: ____“AS FOUND” TESTS2. Do not make any adjustments to KWH Meter in this task.Use the KWH Meter Calibration Formulas for necessary calculations:Watt-Hours = Disc Revs x KhWatts = (3600 x Disc Revs x Kh) ÷ time in secs)Kh = (V x TA x N) ÷ (Disc Revs per hour)Rr = (l0 x1000)÷(MKh x Rs)Kr = (MKh x Rr x Rs)÷ 10,000Multiplier = or x CTR x PTR% Registered = (Mkh x Rt x 100 x As) ÷ (SKh x Rs x N)Max. Demand KW = (V x TA x N) ÷ (Kr x 1000)CR = (V x Meter Class x N) ÷ (Kr x 1000)Full Scale Demand = (CR ÷ 2) or (Meter Class x 10) ÷ RrN = 1, 2, 4, 3 for 1, 2, 2½ and 3 element meters respectively .(For 2½ element meter reverse polarity in middle phase)

METER DATA4. Compare the meter Name Plate with its previous Test Record and verify that Class, Test Amperes, Voltages, Register Ratio (Rr), Register Dial Constant (Kr), Watt-Hour Constant (Kit) and other data are correct.Does the Name Plate data compare with the previous Test Record?Yes: ____ No: ____INSULATION TEST5. Megger the current and potential coils to the chassis and to each other with a 500V DC Megger to ensure no insulation breakdown.Do the current and potential coils have insulation breakdown?Yes: ____ No: ____

CREEP TEST6. Check the meter for creep with only potential transformer connected and load current disconnected.The disc may rotate for part of a revolution forward or backward before coming to rest. This is NOT CREEP.A meter is considered to be creeping if its disc makes a complete revolution in five minutes or less with all load disconnected from the meter and potential coils energized.Did the meter (pass/fail) the creep test? _______________

TORQUE BALANCE TEST (INDIVIDUAL STATORS AT 1.0 & 0.5 PF)7. With all potential coils energized, perform the Torque Balance Test at Full- Load unity and 0.5 Power Factor to each stator in turn and record the % Registration.

8. If the difference between percent Registration of each element is greater than0.5%, re-calibrate in Task 3-2.0.5 PF LAG TEST

9. This test checks that each stator provides the correct flux relationships to measure real power, accurately.With all potential coils energized, apply 3Full-Load current at 0.5 PF and record the% Registration.10. If % Registration is outside the range of 99.5 to 100.5, re-calibrate in Task 3-2.

FULL-LOAD TEST11. Apply 3Full-Load current and voltage at unity Power Factor to all stators and check% Registration.Record the data on the Test Record sheet.12. If % Registration is outside the range of 99.5 to 100.5, re-calibrate in Task 3-2.

LIGHT-LOAD TEST13. Apply 310% load at unity Power Factor to all stators and check the % Registration.Record the data on the Test Record sheet.14. If % Registration is outside the range of 99.5 to 100.5, re-calibrate in Task 3-2.

DIAL TEST16. Dial Test is not suitable for meters with high multipliers (Meters used for Generating Stations and Bulk Customers).Inject Test Amps x Rated Voltage (Normally 120V) at unity Power Factor (Series Test) for a period of one hour and calculate the units.Compare the recording by KWH Standard Meter I KWH Meter under test and find the accuracy.

MAXIMUM DEMAND INDICATION TEST17. Record the time interval of Maximum Demand Indicator (MDI) on the Test Record sheet.Does the time interval of Maximum Demand Indicator (MDI) motor is operating correctly (15min/30min). Yes:____ No: ____Calculate the accuracy of Maximum Demand Indicator in KW.18. Compare the quantities with all available sets of meters and review the readings for any discrepancies.