Smart metering and smart grid technologies are the future of grid systems. There is an increasing focus on the adoption of smart metering solutions as part of various government schemes and programmes. The latest distribution reforms scheme, the Revamped Distribution Sector Scheme calls for the installation of prepaid smart meters for all consumers along with associated advanced metering infrastructure (AMI). It incentivises states and union territories for deployment of prepaid smart meters by December 2023.
With the greater uptake of smart meters, testing their quality and reliability to ensure accuracy in the readings is extremely important. The Bureau of Indian Standards and the Central Electricity Authority (CEA) have notified various standards and technical requirements to ensure the reliability of smart meters. These meters are subjected to various tests to assess their quality and ensure proper functioning.
Standards and technical requirements for meters
The basic minimum technical specifications that should be included in a single-phase whole current smart meter (as per the CEA standards) are the measurement of electrical energy parameters; bidirectional communication; integrated load limiting switch/relay; detection, recording and reporting of tamper events; power event alarms as per IS: 16444 Part 1; remote firmware upgrades; prepaid features at the MDM end (as per IS: 15959 Part 2); TOD features; net metering features (optional as per the requirement of the utility); and on-demand reading.
On the communication side, the meter should be able to communicate with the head-end system (HES) on any one of the communication technologies given in IS: 16444 Part 1 in a secure manner. The selection of communication technology should be as per the site conditions and the design consideration of the AMI implementing agency to meet the performance under the service level agreements.
Testing of smart meters
Smart meters are subjected to testing at all stages of implementation, from designing to installation in the field. These tests include type tests, development tests, load switch capability tests, data exchange protocol and smart meter communicability tests.
Type tests are a series of tests carried out on smart meters of the same type with identical characteristics. They are selected by the manufacturer to test uniformity in the relevant class of meters. They are required to ensure that the product conforms to meter standards. Type tests verify requirements such as insulation properties using impulse voltage test, AC high voltage test, insulation resistance test; accuracy using limits of error, test of meter constant, test of starting condition, test of no-load condition, test of ambient temperature influence, test of repeatability of error and test of influence quantities; electrical requirements using test of power consumption, test of influence of supply voltage, test of influence of short-time overcurrents, test of influence of self-heating, test of influence of heating, and test of influence of immunity to earth fault; electromagnetic compatibility using radio interference measurement, fast transient burst test, test of immunity to electrostatic discharges, test of immunity to the high frequency electromagnetic field, and surge immunity test; climatic influences using dry heat test, cold test and damp heat cyclic test; and mechanical requirements using vibration test, shock test, spring hammer test, test of protection against penetration of dust and water, and test of resistance to heat and fire.
Routine tests are undertaken at the factory to ensure compliance with the standard requirements in aspects of production. Acceptance tests are undertaken at the time of acceptance of meters by the procurer. The acceptance test is a subset of the type test. This test relates to the immunity of the meter and its ability to function under external magnetic influences. The meter is tested for high voltage discharge.
Load switch capability tests are carried out to ensure the performance of the load switch used for remote connect and disconnect. These tests verify if the smart meter load switches are rated to carry maximum current continuously under normal operating conditions and withstand the switching transients during make-and-break operations. The tests carried out on smart meters for load switch capability cover normal operation, electrical endurance, line to load voltage surge withstand, fault current making capacity, short-circuit current carrying capacity, minimum switched current and dielectric strength.
The data exchange protocol supports the interoperability of meters with different makes. The test is used to ensure that the protocol is implemented in all meters and the data from various object identification systems conforms to the set standards.
The smart meter communicability test ensures that the communication modules for wide area network/neighbourhood area network/IHD are approved by the designated agency as per the smart meter standards. The standards provide for the use of suitable communication technologies in the design of smart meters. To assess the communication capability of smart meters, a few tests for end-to-end communication capability and functional requirements are identified. They are included in the relevant standard for smart meters.
The testing is done as per IS: 16444 Part 1 (2015) Amendment 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) encompasses the general requirements and tests for AC static direct connected watt-hour smart meters, Classes 1 and 2. IS 16444 (Part 2) covers the general requirements and tests for AC static transformer operated watt-hour and VAR-hour smart meters, Classes 0.2S, 0.5S and 1.0S. IS 15959 Parts 1 and 2 cover data exchange for electricity meter reading, tariff and load control and companion specification of static energy meters. The manufacturer will have the facility of conducting acceptance testing as per IS: 16444 Part 1. Further, the utility or the consumer can inspect the meter randomly as per the sampling plan for the acceptance test in line with IS: 16444 Part 1.
The way forward
A major challenge in smart meter testing is the lack of adequate testing facilities. Another issue is the long duration of tests, which leads to delays in procurement. With the growing adoption of smart meters, testing requirements are increasing. Various measures are being undertaken to use different samples for different tests, and simplify meter specifications in tenders and anti-tamper requirements so as to reduce the duration of meter testing.
Efforts are also under way to increase the number of meter testing facilities. Recently, in September 2021, the National Accreditation Board for Testing and Calibration Laboratories (NABL) accredited Tata Power’s Smart Meter Testing and Calibration Laboratory located in Mumbai. The NABL accreditation will provide quality assurance to power consumers that wish to install smart meters, thereby providing better control over their energy consumption. This accreditation also authorises Tata Power to extend this support to other utilities in the power industry and further strengthen customer confidence and satisfaction.
Going forward, with the government’s aim to install smart meters for all consumers, the demand for meter testing facilities will increase manyfold. This is essential to create a reliable metering infrastructure for the benefit of both utilities and consumers.
