TYPES OF METER RELATED PROBLEMS IN POWER SYSTEM PART 1

What are the different types of electric meters related problems that contributes to power losses?

Defective Meters
Although electric meters are hardy devices, it is always possible that some of them may develop defects over extended service periods. To ensure that meters on the system will remain accurate, the distributor should implement a periodic meter testing program. Periodic meter testing is required by TVA although testing intervals are not specified. A program meeting current industry standards should be designed so each meter on the system is tested no less frequently than shown in table.

Type of Meter – Minimum Testing Interval
Single-phase, self-contained – 8 years
Polyphase, self-contained – 6 years
Polyphase, transformer-rated – 4 years
High-revenue – 1 year

Table recommends annual testing of high-revenue meters. A working definition of a high revenue meter is any meter is any meter that is associated with more than 3% of the distributor’s total revenue.

A distributor-owned meter testing shop is recommended as part of a sound program for meter testing. In addition to the periodic testing shown in the table, the test shop is needed for special meter tests involving consumer complaints, meter reader damage reports, and similar circumstances. The shop can also be used to test a sample of new meters when shipments are received to provide assurance that vendors are furnishing quality units. If additional personnel are needed to keep up with the testing program, summer college students can be hired for that purpose.

Meter testing procedures should include the following items:

• Check the meter nameplate to be sure it is correct for its application.
• Be sure the internal works of the meter are clean.
• Check mechanical parts such as gears and bearings.
• Check the meter for evidence of tampering.
• Check for creep at no load.
• Run the meter and check for noisiness.
• Perform accuracy checks against a standard meter at heavy load, light load and at lagging power factor.
• Perform a register ratio check.
• Check insulation integrity.
• For multi-stator meters, perform a stator balance test.
• On-site testing should include a complete check of all external wiring.
• For mechanical demand meters, check the interval timing mechanism.
• Zero-adjust thermal demand meters.
• Check the accuracy of thermal demand meters against a thermal demand meter standard.
• Where instrument transformers are in use, check them proper polarity and ratio.
• Be sure that the correct meter multiplier is marked on the meter.

Most meters that fail one or more of the above checks or tests can be adjusted or repaired. Units should be scrapped if the cost of repairs exceeds the cost of a new meter. For those distributors that cannot justify the cost of their own meter testing shop, the use of contractors to do the recommended testing is better than no testing program at all. Case studies have revealed that meter testing is cost effective.

One documented case involves a utility that had no meter-testing program. After carrying out an intensive testing program, this utility reduced its system losses 16% to 11%. In addition to the periodic testing program, meter readers should be instructed to watch for meters that look as though they might have been damaged or otherwise impaired and to report these meters to meter maintenance personnel so immediate testing of such meters can be conducted.

Miswired Meters

The possibility of miswired meters is of the greatest concern with three-phase metering installations. There are many wiring arrangements used for such installations, and most cases involve the wiring of instrument transformers in conjunction with the meters themselves. Because of the complexity of the wiring connections involved, it is not surprising that even experienced metering personnel will occasionally miswire an installation. In many cases, the consequence of the miswiring is that the meter appears to be operation properly, but is actually recording only part of the power being delivered by the circuit.

The remedy for this situation is to check and recheck each polyphase metering installation. Preferably, checks and tests should be made by personnel different from those who wired the initial installation. The connections should be checked lead by lead against meter manufacturers’ wiring diagrams for the type of installation involved. Test procedures outlined in metering manuals can provide further assurance that the meters are wired correctly.

In documented case, a municipal utility serving 100 commercial consumers in the 50-kW to 1,00kW range carried out a program of checking polyphase metering installations. The checks revealed that 40 of the 100 meters were registering an error in excess of 30%, and that all 100 meters were under-recording to some extent. The revenue loss from these defective installations totaled approximately $27,000 per month.

Meter Reading Errors

Misreading of meters by meter readers is not a serious problem with energy meters as with demand meters. Energy readings, measured in kWh, that are incorrect will be corrected automatically the next time the meter is read properly. However, this is not the case with demand meters, which register in kW. If a demand meter is misread as lower than the true reading, the error can never be corrected because the register is reset after the reading is taken.

Emphasis on personnel training and steps to encourage meter readers to take extra care are the first items to address to prevent loss of revenue from misreading. Additionally, computer software associated with the billing system can be used to flag and report readings that depart significantly from the historical trends of each consumer for each season of the year. These computer reports can help identify meter readers who may be making errors, as well as provide a source for searching for possible meter tampering.

Data Entry Errors
Even after a meter is correctly read, the account may be billed in error because the meter reading was not transcribed properly from the meter reading book to the billing system. Where such errors are suspected, the meter book provides a basis for determining if a data entry error did actually occur. Checks of this type can identify personnel who are prone to data entry errors so corrective action can be taken.

Computer software for flagging unusual readings can also be used to identify possible data entry errors. In addition to checks against historical data, the computer can flag readings that are impossible for the type of meter register installed at each consumers’ premises. For example, if a meter reading is on the billing system as 0.00X and the actual register being used reads only X.XX, it is immediately apparent that some type of error has occurred.

TYPES OF METER RELATED PROBLEMS IN POWER SYSTEM PART 2