In line with the digitalisation of power networks, utilities are investing heavily in rolling out advanced metering infrastructure to replace electromechanical meters. This is expected to bring a wide range of benefits to both stakeholders and consumers. Also, given India’s ambitious smart metering targets of 250 million meters, testing the quality and reliability of smart meters so as to ensure accuracy in the recording of electricity consumption and billing is becoming an increasingly important area.
For smart meters, testing is done as per the IS 16444 Part 1 (2015) Amendments 1 and IS 15959 Part 2 (2015) Amendments 1 and 2 for whole current single-phase and three-phase meters and IS 16444 Part 2 (2017) and IS 15959 Part 3 (2017) for transformer-operated smart meters. The communicability test is done on smart meters as per IS 15959 Parts 2 and 3.
IS 16444 Part 1 was adopted by the Bureau of Indian Standards (BIS) in 2015. It encompasses the general requirements and tests for A.C. static direct connected watt-hour smart meters, Classes 1 and 2. IS 16444 Part 2 was adopted by the BIS in 2017 and it covers the general requirements and tests for AC static transformer operated watt-hour and VAR-hour smart meters, Class 0.2S, 0.5S and 1.0S. IS 15959 Part 1 and Part 2 was adopted by BIS in 2011 and 2016 respectively. These standards enable data exchange for electricity meter reading, tariff and load control, and companion specification of static energy meters.
As per the CEA, the technical specifications of single-phase whole current smart meters and three-phase whole current smart meters should include: measurement of electrical energy parameters, integrated load limiting switch/ relay, bidirectional communication, recording and reporting, tamper event detection, power event alarms as per IS 16444 Part 1, prepaid features at the MDM end (as per IS 15959 Part 2), remote firmware upgrade, TOD features, net metering features (optional, as per utility’s requirement), and on-demand reading. The meter shall be BIS marked as per IS 16444 Part 1 and the construction requirements shall be as per IS 16444 or IS 13779.
On the communications side, the meter shall be able to communicate with the head-end system (HES) using any one of the communication technologies given in IS 16444 Part 1 (RF/PLC/cellular) in a secure manner. The meter shall have the ability to record energy under tamper conditions as defined in IS 15959 Part 2 and will log the event and send an alarm to the HES after detection of the defined theft features. The utility or the consumer can inspect the meter randomly as per a sampling plan for an acceptance test based on IS 16444 Part 1.
Testing smart meters
Smart meters are subjected to various tests at all stages of implementation. These include development test, acceptance test, routine test, metrology tests, load switch capability test, data exchange protocol and smart meter communicability test (which is optional). The development test certifies that the meter complies with the product design. The tests for metrology include type tests for parameters such as construction requirements, clearance and creepage distances, display of values, output device and marking.
Type tests are a series of tests undertaken on meters of the same type and having identical characteristics. They are selected by manufacturers to ensure consistency in standard requirements to ensure that the product conforms to meter standards. Type tests cover verification of requirements such as insulation properties, accuracy requirements, electrical requirements, electromagnetic compatibility, climatic influences and mechanical requirements. Acceptance tests are carried out on samples taken from a lot for the purpose of acceptance of the lot. Routine tests are carried out on every meter to ensure that they conform to the requirements and standards.
Accuracy requirement tests can be carried out through tests on limits of error caused due to variation in current, test of meter constant expressing the relation between the energy registered by the meter and the corresponding pulse count of the test output, test of starting condition, test of no-load condition, test of ambient temperature influence, etc.
While testing facilities in India have increased in number, there are still not enough of them. Another issue is the long duration of the tests, which leads to delays in procurement. That said, measures that can help in addressing testing issues include the use of different samples for different tests and simplification of meter specifications in tenders and anti-tamper requirements so as to reduce the duration of meter testing. Going forward, independent testing can ensure that smart meters are subject to the same standards and requirements so as to alleviate consumer and utility concerns.