Meter test practices around the world
Metering International consulted utilities in the USA, Europe, Africa and the Far East, to establish present practices in respect to meter testing and calibration. We are most grateful to Hein Erwin – head of measurements, Eskom Cape Western Division, South Africa, Barry Maindonald – metering and supply engineer, Jersey Electricity Co, Horia Maries – senior engineer, CONEL SC ELECTRICA SA, Romania, Takao Oki - technical co-operation manager, Japan Electric Meters Inspection Corporation (Jemic), Lauren Pananen – meter engineer, Pacificorp, and Ioan Stoica – manager, Oradea power distribution utility, Romania, for their input. This is a summary of their responses.
How often do you test and recalibrate your meters?
In Romania meters are tested and recalibrated according to strict metrological standards, laid down by the Romanian Bureau of Legal Metrology (BRML). These are:
- Single phase induction meters - every 10 years
- Single phase digital meters - every 8 years
- Three-phase induction active power meters - every 5 years
- Three phase induction reactive power meters - every 6 years
- Three phase digital meters - every seven years.
This applies to Class 1 and 2 meters. The higher precision meters have a shorter recalibration cycle of between 1 and 5 years, depending on accuracy. The high precision reference meters are tested yearly.
The JEMIC standards differ slightly. Domestic meters with a rated current of 30, 120, 200A are tested every 10 years, and a rated current of 20, 60A every 7 years. High precision and precision class meters, var-hour meters and maximum demand meters are tested every 5 years.
The Jersey Electricity Co tests and recalibrates meters in line with Schedule 4 of Statutory Instruments 1998 No 1566, Electricity, the Meters (Certification) Regulations 1998.
Pananen reports that Pacificorp has two test programs – periodic and sample. Periodic selects commercial meters on a 1, 2, 5, 8 and 16 year cycle. The size of the load determines how often the site is revisited. The residential sample meter program uses ANSI/ASQC Z1.9 standard for selecting and analysing test results for homogeneous meter groups (i.e. I70, D5, J5 etc).
According to Erwin, all large power users in South Africa (customers > 100 kVA) are on a strict calibration/maintenance programme. The calibration cycle will vary from 2 to 5 years depending on the size of the metering point.
How do you select a batch of meters for testing?
Oki points out that JEMIC provides a verification service for all the electricity meters used for tariff or certification purposes, and that a batch of meters is thus never selected for testing.
The situation is similar in Romania, according to Stoica, and is once again the subject of legislation by the BRML. He says that on this basis the utility tests every meter piece by piece. Maries adds that the date of periodical testing is a function of the date last tested. Every meter is tested after the validity period has expired.
The same is true in South Africa, where every energy meter is calibrated and issued with a traceable certificate; therefore batch testing is not performed.
At Pacificorp batches are selected by random sample or by date of last test. And Maindonald adds that meters selected for testing are typically all of the same rating and/or manufacturer.
Do you refurbish meters?
This is not a function performed by JEMIC, but Oki confirms that repair companies in Japan do refurbish used meters. At Pacificorp and Eskom meters are not refurbished, although Erwin points out that the 10-year lithium battery is replaced when the meter comes in on its calibration cycle. Refurbishment is carried out at the Jersey Electricity Co.
Stoica says that out of order meters, as well as those which have measurement errors but are still within their prescribed lifetime, are fixed if the problem is not irreversible. All the refurbished meters are recalibrated. According to Maries, meters are only refurbished in particular cases. More usually the utility retrofits meters (for example adding remote reading capabilities to electromechanical meters) as well as upgrading electronic meters to add new functions.
Do you perform incoming tests on new meters?
This is very much what JEMIC exists to do – provide a verification service for all the electricity meters used for tariff or certification purposes.
Pananen confirms that Pacificorp follows the ANSI C12.1-1995 recommendation of 100% testing by the meter manufacturer or the electric utility. Pacificorp does verify the meter manufacturer’s certified test results by testing 96 meters out of a lot of 6 000 and comparing the results with the manufacturer’s tests. He points out that this also provides some quality assurance on these products.
Eskom tests all the meters it receives, and calibration results are stored in a database which is linked to the metering point and customer data.
Romanian standards hold that the existence of the metrological reports that are attached to the new meters represent a guarantee of good working. However, says Stoica, the new induction meters are tested piece by piece; those that do not perform at the required level are sent back to the manufacturer when the number is very large, or are fixed in the utility’s lab.
Maries confirms that 100% of the new meters are tested, while Maindonald says the Jersey Electricity Co purchases new meters which are certified. The utility undertakes sample tests, the sample size being in accordance with BS6001 sampling procedures.
What equipment do you use for testing/calibration?
Oki says JEMIC uses an automatic watt-hour meter testing system which it developed for calibration. The JEMIC uses AC-DC Power Comparator, which is the national primary standard developed by the JEMIC.
A three phase Ganz (Hungary) testing board standard meter EHF-33-H2, a three phase Metra (Czech Republic) testing board standard meter EHF-33-H2 and a single phase IRCOMON (Romania) testing board standard meter EHF-3 are used by Stoica and his team for testing/calibration.
Maries says the utility uses different types of standard semi and fully automatic single phase and three phase meter test stations, class 0.2 and 0.5, including older design test stations. Recently a 24 piece three phase fully automated class 0.5 meter test station for 20 meters, manufactured by EDI, a UK company, and a 2 piece fully automated, single phase meter test station for 40 meters, manufactured by Meter Test Equipment AG, Switzerland was procured for the Romanian DISCOs (the 42 subsidiaries forming part of CONEL).
Pananen’s team makes use of a WECO 2100 electronic test board mounted in the meter van. And Eskom uses energy standards from Landis & Gyr, all of which, says Erwin, are traceable to South Africa’s National Measuring Standard for electrical power/energy.
Maindonald reports that the Jersey Electricity Co is about to relocate its meter test station, and is purchasing fully automatic test equipment to replace the present outdated equipment.
How many staff are employed to deal with testing/calibration?
Oki says the JEMIC employs 825 inspectors, involved in verification services for all the electricity meters. Stoica states that Oradea has 31 persons dealing with the matter - 4 x 2 in the utility, 22 in the central laboratory.
In CONEL’s 42 subsidiaries (DISCOs) between 15 and 75 persons are employed who deal with meter testing/calibration. The actual number depends on the number of installed meters. Maries says this varies between 85 000 and 290 000 single phase meters, except for the Bucharest DISCO where 820 000 single phase meters and 35 000 three phase meters have been installed. In the whole of Romania some 1 100 persons are employed to deal with testing and calibration of a total of 8 million single phase meters and 530 000 three phase meters.
Pananen says that Pacificorp has about 90 training meter journeymen servicing a 1.3 million meter system. The Jersey Electricity Co employs only two staff in testing/calibration, but Maindonald confirms that the meter storeman/mechanic and meter technician are involved in some related activities.
Do you conduct field tests as well as laboratory tests?
At Pacificorp Pananen says that all tests for periodic and sample testing are done in the field. Only the verification tests are done in a meter shop. Oki confirms that the JEMIC conducts field tests for follow-up surveys every four years.
In Romania field tests are not recognised by the BRML. Stoica reports that Oradea does test the accuracy of meters in the field, but since the tests are conducted at the actual meter load as opposed to a range of loads, they are not recognised metrologically. When meters tested in the field do not fulfil precision requirements, they are changed. He believes, however, that field tests cannot replace laboratory tests.
Maries says that the utility intends to try to obtain approval from the BRML in order for field tests to be recognised as valid. To this end the DISCOs have recently acquired 156 pieces of high precision portable reference meters (class 0.5 single phase, class 0.05 for three phase).
Erwin feels very strongly that tests/calibration should be carried out in the laboratory, using staff who are trained and experienced in the tasks required. He points out that field staff are often pressed for time, which could affect the reliability of the test results. Taking meters which have been tested and calibrated in the laboratory into the field means that the minimum time is spent on site, as a freshly calibrated meter is exchanged with the "old" meter in the field.
In addition he believes that an energy meter which is hermetically sealed should never be opened in the field. From an audit point of view, only the calibration laboratory’s seal of approval should be placed on the meter cover; the field staff seal will be placed on the terminal cover. Erwin maintains that this gives the utility and its customers the confidence that there are no field staff roaming the field, opening and adjusting meters – lawfully or unlawfully.
It has been interesting to note the different approaches of the various utilities to aspects such as batch testing and field tests, and once again we thank the respondents for sharing their views with us.