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When talking about power metering most people think about the smart meters they have at home. Some of you may think of the simpler kWh meters used for cost allocation or sub-billing in buildings and industrial applications. These power quality meters are very good for what they are designed for, but there are some critical applications where the metering performance needs to be more reliable.
In general, these critical applications can be divided in two groups:
- Revenue metering: relevant where large amounts of energy (and money) are changing hands. That is the case, for example, at interchange points between generation and transmission, or transmission and distribution utilities.
- Power quality monitoring: the impact of poor power quality can be catastrophic to critical power users, impacting industrial processes, damaging electrical assets and putting entire businesses at risk.
Not surprisingly, the criticality of these applications is directly linked with the financial impact they can cause to stakeholders.
Another important aspect to take into consideration is the fast (and accelerating) transformation of the electrical grid.
Distributed generation, renewables, electrical vehicles and modern power electronics are changing the grid characteristics which can affect the way power quality meters perform and how accurately they can measure various electrical network parameters.
In this context it is imperative to use advanced power metering; more robust, with higher accuracy and faster sampling rate. But how to be sure these advanced meters are truly reliable? How to make sure they accurately measure and monitor electrical networks?
The answer involves everyone’s favorite topics: standards!
Regulating accuracy
There are a several foundational international standards published by ANSI, IEC and OIML that specify requirements for solid state energy meters: ANSI C12.1, C12.20, IEC 62052-11, IEC 62053-2x and OIML R-46.
These standards define general and particular requirements, tests and test conditions for static energy meters.
Meters to be used in revenue billing applications must comply with these standards and the vast majority of local regulations and requirements for billing meters, such as those for Measurement Canada, European MID, Brazilian Inmetro, Mexican NOM001, Australian NMI M-6 are effectively based on ANSI, IEC or OIML documents.
The important point to note here is that both ANSI and IEC standards have gone through significant updates recently, and a significant revision of OIML R-46 is under way.
These new revisions provide the benefits of higher accuracy class 0.1 metering, increased meter robustness, and increased metrological performance with highly distorted signals.
Power Quality Instruments – PQIs
Most digital electricity meters produced today can calculate and report on some kind of power quality metrics, but these measurements have been found to differ substantially between manufacturers.
The standard IEC 61000-4-30 was created to address this discrepancy by defining a set of measurement methods and algorithms for each of the Power Quality metrics.
Unfortunately, when the standard was first released, there was no traceable and repeatable procedure to verify conformance. Significant differences in measured Power Quality metrics could still be found between device manufacturers.
This situation was one of the main drivers for the development of the IEC 62586 series of standards.
Part 1, IEC 62586-1, was constructed as a comprehensive PQ instrument (PQI) product standard. The standard outlines safety, electromagnetic compatibility (EMC), climatic, and mechanical requirements.
These requirements serve to ensure the instrument’s robustness will be suitable for its installation within the severe environments of a power station or a substation.
Part 2, IEC 62586-2, defines the functional tests for verification of compliance of a PQI with the measurement methods defined in IEC61000-4-30 standard.
IEC 62586-2 also includes tests to assess the impact of external power system influences (such as voltage and frequency changes, harmonics) and temperature on the PQI performance.
Effectively, the IEC 62586-2 provides a comprehensive, repeatable and traceable test procedures which allow unbiased comparisons of performance of different PQIs.
Truly reliable power quality meters for critical applications
The evolution of foundational standards for energy accuracy and power quality monitoring are a clear indication that the electrical grid changes are significant and that manufacturers need to constantly evolve the design of power quality meters used in critical applications.
The new IEC and ANSI accuracy requirements (ANSIC12.1 / C12.20 – 2015 and IEC62052-11 ed 2:2020/ IEC 62053-21, -22, -23, -24 ed.2:2020) make revenue meters more suitable for use on modern electricity distribution networks and result in meter designs updated to match the technical progress in metrology, and the increased customer expectations of more robust and more accurate measurements in billing applications.
Energy meters that comply with the latest editions of these standards will provide confidence that they will be more accurate in highly polluted electrical networks and will have better overall metrological stability.
On the Power Quality side, compliance only with IEC61000-4-30 is not enough anymore. Critical power users need to ensure their power quality monitoring devices are tested properly (IEC62586-2) and will keep their accuracy and performance level in a real substation environment, under the influence of several different environmental and electrical conditions (IEC62586-1).
It’s also important to remember the value of certifying the metering devices using an independent third-party laboratory. Third party certifiers provide an objective review against the standards, free from the economic demands of the marketplace, increasing the confidence in the device’s performance and reliability.
Finally, as the substations become more connected, cybersecurity also becomes a key feature for which true reliability should be assured. Secure communications, access control, and general robustness of the cybersecurity solution can be effectively demonstrated by compliance to the relevant international standards, such as IEC62443.
To learn more about the topics discussed here, please take a look at the white papers below:
