Energy meters form a vital instrument of revenue realization for the distribution utilities. Based on the meter reading, the utilities submit their bills to consumers for realization. Inaccurate/faulty recording may become catastrophic both to consumers and utilities. Thus, a need to ensure a high degree of performance and reliability from the meters has become important. The meters are tested and calibrated to ensure proper working and that the accuracy is to be maintained within permissible limits under IE Rules.
In Routine Tests, Meters are calibrated such that the overall accuracy is within the percentage error limits. All initial calibrations of meters are performed in a laboratory or test house. The most common method for testing meters is to inject voltage and current from a stable power source in combination with a reference meter.
The main requirement in a test lab will be: Test bench, Reference standards, Power source, Software and Accessories.
The test bench could be for single phase or three-phase meters, electromechanical or electronic. It could be fully automatic, semi-automatic or manual. As per the Indian Electricity Rules, the meters in service need to keep to the prescribed accuracy range. With time, the accuracy of the Ferrari’s meter degrades and the meter tends to slow down. For that, periodical testing of and recalibration of all meters installed in the field for all categories of consumers need to be carried out as per the meter standards. The test schedule as per the Central Electricity Authority Regulations on Installation and Operation of Meters is given in the Table.
Methods of Testing
Irrespective of purpose, testing is generally carried out
• on site, or
• in a Meter Testing Station (MTS) accredited as per IS/ISO/IEC 17025. On-site testing may be carried out.
i)under actual prevailing load; and
ii) by injection method after connecting a suitable phantom load or a resistive load.
The routine testing of meters should be carried out once in 3 years. In addition, surprise checks should be conducted at the consumer’s installation and meters should be checked from time to time. The important points to be paid attention to while checking are given in Box.
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