Energy meters are a key component of the supply system and their reliable functioning is essential for accurate registering, controlling and monitoring of power consumption. Improvements in energy meter technology have brought in value-added features such as remote sensing, LCD display and recording of tampering events, and made the meters more compact. Today, meters have grown from simple measurement tools into smart, automated, wireless reading devices. With these technological changes, meter and meter component testing considerations have expanded to include stringent electromagnetic compatibility (EMC), product safety and environmental requirements. The testing process is crucial for assessing the reliability of energy meters. From testing observations and results, manufacturers and utilities can evaluate the reliability and quality of the product. The main objective of testing is to ensure that meters are designed to comply with the relevant standards and customer specifications. Testing also helps establish the reliability of meters in respect of their electrical and mechanical design.
Meter testing standards
The Bureau of Indian Standards has formulated certain standards for meters to ensure design uniformity, resolve interoperability concerns and streamline the process of meter testing. In the case of smart meters, testing is done as per the 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. IS 16444 Part 1 is based on IS 13779, IS 15884 and IS 15959 Part 2. Meanwhile, IS 16444 Part 2 is based on IS 16497 and IS 15959 Part 3. The communicability test is conducted on smart meters as per IS 15959 Parts 2 and 3. For testing meters under IS 16444, three samples are collected for type tests, one for load switch tests and one for data exchange protocol at the optical port and communicability tests. Thus, meter standardisation is of paramount importance.
Types of meter tests
The key meter tests include type test, routine test and acceptance test. The type test is undertaken to prove the general quality and design. Routine tests and acceptance tests are undertaken at the factory/manufacturing premises and at the time of acceptance of a particular lot of meters by the procurer.
Tests on meters can be categorised as per the following:
- Tests of insulation property: This test is used to check the basic insulation between live parts and the body of the meter to protect against electric shock.
- Tests of accuracy requirement: The purpose of these tests is to verify the performance of the meter during various power line abnormalities.
- Tests of electrical requirement: These verify the meter design with respect to electrical parameters in the field and withstanding capacity under fault conditions.
- Tests for electromagnetic compatibility: These tests are carried out to check meter immunity for electromagnetic radiations and its interference.
- Tests for climatic influences: These tests are carried out to determine the ability of the meter and its components in extreme non-operating conditions or during storage.
- Tests for mechanical requirement: The purpose is to determine any mechanical weakness or degradation in the specified performance of the meter.
Besides these, smart meters must also be subject to metrology tests, load switch capability tests and device language message specification (DLMS) protocol verification. The load switch capability test assesses the performance of the load switch used for remote connect/disconnect. The DLMS protocol verification is the last stage of meter testing. The purpose of this test is to verify the interoperability between smart meters and other equipment in a system that helps undertake a comprehensive assessment of meters. In addition, tests are required to be done to meet large numbers of anti-tamper features as per the purchasers’ tender specifications.
For better reliability, energy meters have to undergo various EMC tests, in which meters are compared under various normal and abnormal conditions to ensure their accuracy in the field. This calls for adequate availability of meter testing laboratories with advanced facilities. Although the testing process is time-consuming and expensive, it is important for ensuring the reliability of energy meters. During type testing, failure in any one test results in non-compliance with the required standards; hence, each and every test is equally important. Utilities are continuously adding various tests to their tender specifications in order to make energy meters more reliable, as revenue collections depend on the accurate functioning of meters. Understanding their requirements and accordingly adding logical features to meters, as well as making them compatible with the standards is an important task for meter manufacturers.
In sum, it is essential for distribution utilities to install good quality meters. This would be possible only if there is standardisation of tender documents, greater focus on research and development for enhancing meter design, setting up of additional meter testing laboratories, and an improvement in testing efficiency.