A good metering system provides an insight into the entire spectrum of distribution system operation, measures the data accurately, is reliable and improves system efficiency. A smart meter, therefore, should be carefully designed to withstand surges, fast transients, and temperature and humidity conditions much beyond standard conventional meters.
The Bureau of Indian Standards (BIS) has defined metering standards to help undertake a comprehensive assessment of meters. While some of the standards for conventional meters, including IS 13779 and IS 14697, have been in existence for almost 20 years now, those for smart meters (IS 16444) were established in 2015 and amended in 2017. Prior to this, different states were issuing different specifications for smart meters and it was difficult to test them on uniform technical requirements. The smart meters being installed need to be tested for their performance and compliance with standards.
Standards for smart meters
In August 2015, BIS published the smart meter standard IS 16444, consisting of two parts. Part 1 covers the general requirements and tests for alternating current (AC) static direct connected watt-hour smart meters (classes 1 and 2), while Part 2 covers AC static transformer operated watt-hour and VaR-hour smart meters (classes 0.2S, 0.5S and 1.0S). IS 16444 covers single-phase energy meters and three-phase energy meters (with and without net metering facility). In March 2016, another standard, IS 15959: Data Exchange for Electricity Meter Reading, Tariff and Load Control – Companion Specification for Smart Meters, was revised and published as IS 15959: Part 2 Smart Meter. This standard specifies the protocol and communication testing requirements and is applicable to smart meters designed as per IS 16444. Further, the functional requirements and technical specifications of smart meters as well as advanced metering infrastructure (AMI) have been laid down by the Central Electricity Authority (CEA). The technical specifications developed by any utility must adhere to BIS standards and CEA specifications.
Key design considerations and challenges
One of the considerations to be kept in mind in terms of expectations from a meter is to accurately measure various types of load applications, which withstand field environmental conditions. Further, the metering component should not be impacted by field electrical conditions. There should also be immunity against tampering. Other considerations include easy availability of meters at economical costs, storage of metering data, and compliance of products with the operating life need.
Meter designers, need to finalise suitable design architecture and validate the design as per user needs for product reliability. Proper selection of components and setting up of appropriate manufacturing processes are also necessary. At the manufacturing stage, appropriate process selection in terms of material, volume and tolerance is required. To make the design less complex, emphasis should be laid on eliminating and combining unnecessary processes. The use of metallic shield parts adds manufacturing complexity and may increase product weight and size. Moreover, assembly designs should have minimum components with well-thought-out wire designs and constraints.
Some of the major challenges that arise as per the field conditions are ensuring accuracy within the limit for the product lifetime and operation of the product at different temperature and humidity levels. Further, the use of high speed and multilayer printed circuit boards adds to the cost and impact supply chain due to the longer lead time. Moreover, an increase in the use of an extra filter component may impact product reliability.
The way forward
A significant advancement in the digitalisation of grid systems has been the shift from conventional meters to smart meters. Going ahead, smart meter technology will be at the forefront of enhancing the functioning of the grid system. While smart meters today provide a lot of data pertaining to power consumption, with further advancements in technology, they will also be able to directly measure the total harmonic distortion (THD). At present, the DLMS protocol standard IS 15959 does not address the power quality/THD parameter on the object identification system (OBIS) list. Hence, the THD parameter must be defined for OBIS. Another change that needs to be brought in is with regard to the metrological parameter, where the effect of harmonics on reactive power is not related to the functionality. Efforts in this regard will help discoms perform better analysis.
Each test, at every stage, has its significance because during “type test”, failure in any one test results in non-compliance with the standards. Further, with the growing adoption of smart meters, the number of meter testing laboratories needs to be increased. More reliable, state-of-the-art facilities are needed to cater to the growing test requirements.
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, and research and development for improving meter design and testing capability would go a long way in improving metering infrastructure.