Meter Testing Simple Word but deeper impact

Meter Testing Requirement in Accridated Laboratory
December 31, 2020

Meter Testing-A simple word but deeper impact

When the word “meter testing” popup anywhere in the metering community, most of the time this issue is taken quite lightly. Despite that, this activity plays very significant role in the consumer satisfaction, revenue protection, quality control, compliance with regulatory requirements and image building.

Complexities of the modern meters which includes the several parameter measurement & recording at the same time, power quality related measurements, communication technique and additional functionalities related to billing & tariff etc. has increased the importance of meter testing while manufacturing, accepting or testing at site.

The poor quality meters which are available plenty in the market, has increased the role & responsibility of meter testing division many folds, to ensure that basic energy measurement are done properly at least.

To understand the meter testing world lets first understand who test, when, why and how….

1.0 Meter testing practices around the world

Worldwide energy meters are being tested at the several places in the chain starting from manufacturer to consumer to serve the various objectives. The survey reveals the further useful information and practices are used around the world.

Who test Meter Manufacturer Electric Utilities in Laboratory Electric utilities at site
  • To ensure the quality of meter
  • As part of purchase agreement
  • To comply with standard’s requirements & verify the accuracy of meter as per standard
  • To ensure proper functioning and features
  • To check the measurement accuracy
  • Quality control and inspection of meters
  • To solve the consumer complain
  • To ensure proper functioning of meters
  • To evaluate the installed meter population
  • To form basis for replacement or continuation or maintenance or calibration decision
When At the production stage, after assembling the meter While receive the meter from the supplier

OR, while sending the meter for installation at consumer places

  • On complain basis
  • On regular interval basis to ensure the proper functioning of meters
Rate of testing 100% of manufactured meters There is no common but following practices revealed from the survey

  • 100%
  • As per sampling plan e.g. 4% of lot
  • No testing for electronic meters
  • No testing at all
There is no common concept but following practices revealed from the survey.

  • On demand basis which may be originated from consumer or billing department
  • As per sampling plan
  • Once in a year for large consumer
  • No testing at all, just replace the meter after certain interval or complain basis
Testing Practices & Methods Using Stationary meter test benches to meet large testing volume Using stationary meter test benches to meet the large testing volume Using portable phantom load and reference standard. See details in onsite testing practices & methods

1.1 Testing in laboratory

Energy meters are being tested in laboratory by manufacturer before shipping to utilities and by utilities before installing the meters. As mentioned above both the parties have more or less same objectives and use the stationary test benches. It seems to be simple but still offers the great challenge in doing laboratory testing. Mainly are as follows:-

  1. Efficient and proper testing of large volume of meters in minimum duration. To achieve this objective, each aspect of meter testing should be taken care e.g. process optimization, quick connection of meter, multi-functional testing, data administration.
  2. New design of meter, which includes testing or verification of complex features, functionality and communication with electronic meters using IR scanning head, PLC, RS485, Mod bus or other known method.
  3. Testing of closed link meters.
  4. Maintaining the in house legal metrology system, without removing the reference standard from bench in a shorter duration using high precision comparator and automatic testing. The new design of benches offers the special hardware and software, which save time and money in comparison with sending the reference standard to external lab.

1.2 Onsite testing practices & Methods

On-site meter testing is gaining in importance among electric utilities around the world. The reasons are to ensure the revenue, comply with regulations and improve customer satisfaction. All the reasons are primarily centered on the correct recording of energy consumption. Correctness of energy recording is in turn dependent on meters instruments transformers.

The onsite testing methods differ from country to country. The methods are mainly influenced by

  1. Access to meter site, for example in Asian countries access of meter and removal of the meter connections are difficult and restricted to limited authorities to prevent energy theft
  2. Testing Regulation & practices: Some countries legally accept on site testing when the meter is tested under similar condition to laboratory testing i.e. using a phantom load

The onsite testing methods are mainly as follows:-

1.2.1 On-line testing at consumer load

In this method the tester connects the reference meter to the meter under test, i.e. voltage in parallel and current in series using clamp on CT. This is a quick & economic method but tester has to rely on running consumer load. The objective of such testing is to check the connection and any existing tamper condition and to get a fair idea of the accuracy of the installation.

1.2.2 Off-line testing using phantom load

In this method operator disconnects the meter under test and connect it with electronic phantom load. There are two kinds of phantom loads available to cater for different needs and practices

  1. Current phantom loads, in this method, test voltage is fed from incoming mains supply. The magnitude and phase angle of the test current can be varies as per the test points and synchronized with incoming mains voltage supply.
  2. Voltage and current phantom load, in which electronic phantom load generates the required test voltage, current, power factor, frequency. These test parameters are independent of mains supply voltages.

Automated and uniform testing on all meters is possible by using these modern phantom loads along with a reference standard and software. The result achieved by the uniform testing can be further systematically utilized.

This method is a bit time consuming and requires a phantom load compared to online testing method, but it is closer to laboratory testing. This method is currently used in the European countries which have developed their standard & regulation accordingly.

1.3 Testing Intervals

Testing intervals do vary from country to country. Survey reveals the following information.

Name of country Interval information Remarks (additional information)
Germany Once in 16 years for electromechanical meters

Once in 8 years for electronic meters

If pass then both type of meters will be reused for another 4 years

When such testing performed on sample basis then whole population of meters will be accepted if samples pass the acceptance criteria, if not then whole population will be replaced

Testing generally performed in Laboratory

Austria Once in 20 years for electromechanical meters

Once in 8 years for electronic meters

If pass then both type of meters will be reused for another 4 years

Testing generally performed in Laboratory

Denmark Once in 16 years for electromechanical meters

Once in 8 years for electronic meters

If pass then both type of meters will be reused for another 4 years
India Once in 2 year for bulk consumer, and once in 5 years for domestic consumer

Before installation

On site testing as per CEA guidelines

Laboratory testing

Israel 2-8 years depend on metering mode, meter type and experience Mainly Laboratory testing
Hong Kong No planned testing Meters only tested when installed and annual maintenance of meters for large customers
Kenya Once in a year for large customer On site testing
Ukraine Once in 6 year Also depend on meter type, manufacturer
Croatia No planned testing
Colombia Vary from utility to utility
Singapore Once in a year for large customer On site testing
Thailand Once in a year for large customer On site testing
Russia Once in a year for large customer (at the field condition)

Once in 8 years at laboratory condition

100% of the billing meters (but not always fulfilled due to lack of infrastructure)

100% of the meters

Romania Once in 10 years Laboratory testing

2.0 Scenario of applicable standard

2.1 For meter testing in laboratory

Following standard defines the tests, test conditions, and acceptance criteria for meter testing in laboratory according to meter type and class of accuracy.

  • IEC 62052-11, IEC 62053-11, 21,22, 23 & EN50470 series

Apart from international standard most of countries either have adopted the IEC standard as it is or modified to suit the local conditions. For example Indian standard IS 13779, 14697,

2.2 For meter testing at site

There is no international standard exist for such testing. Generally same limit as defined for laboratory testing or with some concession for environmental influence are used.

For example in Australia class 0.5 meter should be with 0.7% limit for on-site testing. In Kenya 3% error is allowed for class 2 electromechanical meters. In Hong Kong +2.5% to -3.5% error is allowed for class 2 meters

Several attempts are being made to define the tests and tests conditions. For example

  1. Italian standard (draft stage) which defines the testing of various metering installation including CTVT
  2. German standard (draft stage), specially designated to on-site testing and testing equipment.

3.0 New findings: – Additional error in measurement

The power quality has decreased drastically due to several reasons like pollution in power supply due to SMPS, rectifier loading etc. In these circumstances the conventional meter will not be able to record the energy accurately. Studies conducted in the recent years reveal that

  1. If there is small amount of DC voltage (e.g. 200mV) in the voltage circuit of meters then this mixed signal would cause significant additional error in energy measurements. This kind of situation can prevails in LT CT operated/whole current installation.
  2. Recent studies[1] indicates that energy meters which use the mixed core CT to measure the current signal will give high error in power measurement when signal is mixed. This kind of situation can be seen in dryer, vacuum cleaner or any other load uses the typical asynchronous motor, phase shifting or diode for output control purpose.

4.0 New trends in meter testing

4.1 Laboratory testing

Latest design of test benches offer the highest degree of process automation which includes the facilities beyond conventional testing (i.e. accuracy testing and other test as per standard) like automatic handling-connection of meters, pulse i/o testing, adjustment, parameterization, other functional testing. These types of benches are useful for volume testing.

4.2 On site testing

In the recent years, scope of onsite meter testing has been expanded beyond simple accuracy testing. This trend has seen often in European countries. Now Onsite testing also includes the following task/testing/analysis.

  1. Connection check by using vectorial display & Instantaneous parameter. This help to detect the tamper or correct the wrong wiring
  2. Harmonic analysis:- Detailed harmonic analysis is being done to investigate
    1. which harmonic is causing problem
    2. Is it generated by consumer or already in the network
  • Burden measurement:- To ensure that CTVT are not over/low burdened
  1. Accuracy testing of instrument transformer (ratio and phase angle errors)
  2. Complete site testing by using High voltage sensor. That means complete site including CTVT and meter can be tested without dismantling them.

5.0 Conclusion: – Value addition by meter testing

The simple word “meter testing” can do significant value addition for both manufacturer as well utilities. The maximum and long term beneficiary will be electrical utilities provided they integrate this activity properly and systematically in their distribution management system. The meter testing at utilities can do following value additions.

  1. Statistical evaluation of meter type, brand, performance of meters after given years of operation, which further helps deciding on test interval.
  2. Qualitative feedback for future procurements of meters and instrument transformers.
  • Detection of theft through regular and extensive testing at site.
  1. Screening of a particular area or zone so that surveillance interval/frequency of particular zone can be increased or decreased.
  2. In terms of customer confidence, minimizing customer complains & legal cases, and image building.

“The revenue for a utility will come only via meter and measuring component CTVT, hence its proper & accurate working for a long term will be challenging & interesting for a utility.” Y.K.Nama

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