Meter testing is required to assess the quality of meters installed in the field. It is undertaken at various stages of the meter development process to ensure that the design and functionality requirements are met. The Bureau of Indian Standards (BIS) has defined metering standards to help undertake a comprehensive assessment of meters. Both meter manufacturers and procurers are responsible for the quality of meters. While the former needs to expand its testing facilities and undertake research and development (R&D) to improve meter design, the latter needs to identify reliable manufacturers with a proven track record for quality procurement.
Types of tests and their benefits
Meter testing is required at all stages of meter development, right from the designing of meters to their installation in the field. The development test is undertaken to ensure that the meter design complies with the established standards while the type test helps ensure that the meter complies with product standards and secure type approval. Two other important tests are routine tests, undertaken at the factory: and acceptance tests, undertaken at the time of acceptance of meters. Besides, meters undergo specific type tests or acceptance tests, which help assess whether they comply with specific conditions set in the tender documents.
Meter testing is necessary to improve the reliability and accuracy of performance. It also prevents meter malfunctioning. These tests help predict how long meters can operate without any degradation in performance. They also assess the anti-tampering features of meters and the performance of meters in a poor power quality scenario.
The standardisation of meters is of paramount importance as it ensures uniformity of design, resolves interoperability issues to a certain extent, and makes the process of meter testing more streamlined. The BIS has established standards for meters. These include IS 13779 (up to amendment 5) for single-phase and three-phase conventional whole current meters; IS 15884 for single-phase/three- phase prepaid whole current meters; IS 14697 (up to amendment 4) for three- phase transformer-operated meters; and IS 15959 Part 1 (up to amendment 4) for data exchange protocol. In addition to this, tests for solar radiation and ingress protection, namely, IP54, need to be performed for outdoor meters.
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) amendment 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 done on smart meters as per IS 15959 Parts 2 and 3. For the testing of meters under IS 16444, three samples are collected for type tests, one sample for load switch tests and one sample for data exchange protocol at the optical port and communicability tests.
Meter testing and quality procurement
One of the key concerns pertaining to meter testing is the long test duration that leads to delays in procurement and subsequently in payment. Typically, all type tests take 40-60 days, acceptance tests one week, and type tests along with tamper, tender and protocol tests take 80-90 days. Further, testing of prepaid meters, which involves a large number of tests, takes four to five months. In order to reduce the duration of meter testing, it is essential to identify key tests from the list of standard tests for a meter, identify anti-tamper requirements and ensure clarity of specifications. Besides, separating samples for unrelated tests helps in saving meter testing time. By submitting separate samples for type tests, additional tests and protocol tests, the testing time can be reduced. Besides, different tests should be performed on meters from different lots.
With regard to the testing of meters at the manufacturer’s end, there is immense scope for the improvement and expansion of testing facilities. In order to meet the advanced metering requirements and ensure accurate metering, meter manufacturers need to develop in-house R&D and testing facilities.
They need to clearly understand the meter standards and tender specifications, and should not comply with ambiguous tender specifications. Besides, acting on feedback on the operation of meters in the field, analysing instances of meter failures, and adopting proper quality control methods and procedures could help improve the meter testing capacities of manufacturers. Meanwhile, for procuring quality meters, the procurer needs to analyse the capacity of meter manufacturers in terms of quantity and quality. It could undertake vendor analysis taking into account the rating of the manufacturer based on its previous orders and in-house testing facility, among other things. In addition, test reports from reputed laboratories, acceptance tests and other reliability tests could help in quality procurement of meters. Apart from this, the tender specifications should focus on reliability and not complex anti-tamper features and other unwanted parameters.
Accurate metering has a significant impact on discom revenue as consumer bills are the only source of revenue for discoms. Therefore, it is required to ensure that there are no unusual deviations in consumption and maximum demand readings in meters. Further, issues such as malfunctioning of meters due to the poor quality of power supply and failure of meter LCD display need to be addressed. In the case of smart meters, reliability and communication tests should be undertaken. Meanwhile, there is an urgent need to standardise the tender specifications for meters. This would help meter manufacturers and procurers alike by streamlining the procurement process and technical functionalities of meters. Often, the tenders for procuring meters carry complex specifications, particularly regarding anti-tamper requirements. This is because the simulation of tampers is different at each laboratory. There is also no clarity on the specific requirements of procurers.
An important requirement for meter testing is ensuring adequate availability of meter testing laboratories. Further, more reliable, state-of–the-art facilities are required to cater to the growing test requirements. This has become even more relevant with the growing adoption of smart meters, which entail special testing requirements and longer test durations. The minimum test duration for smart meters is 45-50 days. Central Power Research Institute (CPRI) laboratories for meter testing are operating in Bengaluru and Bhopal. The CPRI smart meter testing lab in Noida is expected to be ready shortly. Meanwhile, the CPRI laboratory for meter testing at Nashik is expected to be completed within the next three years.
Apart from this, in order to improve the metering testing and standardisation scenario, a number of measures have been proposed, which are currently under consideration. These include harmonising of the Indian Standard (IS) and the International Electrotechnical Commission, introduction of standards for direct current meters and panel meters, and review of IS 15884.
To conclude, the installation of good quality meters is essential for the health of the distribution segment. To this end, standardisation of tender documents, expansion of meter testing laboratories, R&D for improving meter design and testing capability, etc. would go a long way in improving the metering infrastructure.
Based on a presentation by B.A. Sawale, Additional Director, CPRI, at a Power Line conference