[Yogesh Nama][November 24, 2006]

INTRODUCTION

Energy meters are being tested worldwide to meet the needs of both manufacturers and consumers. The author has conducted a small informative survey of global practices, and people with knowledge of meter testing from countries like Germany, Norway, Singapore, Thailand, Hong Kong, Romania, Hungary, Russia, Croatia, Colombia, India, Israel, Kenya and Egypt provided information about the meter testing practices in their region. This paper is primarily based on the results of the survey and the experience gained through working in this field over the last 15 years.

TESTING SCENARIO

The table below explains who tests the meter, when, and what are the objectives served by the meter testing.

Who Meter Manufacturar  Utilities in labratories  Utilities at consumer sites 
When At the production stage, after assembling the meter  After receiving the meter from the supplier; or when sending the meter for installation at consumer premises  When a complaint has been received; or at regular intervals to ensure the proper functioning of meters 
Rate of testing 100% 

There is no common ground here. The survey revealed the following practices:

  • 100%
  • As per sampling plan, e.g. 4% of lot
  • No testing of electronic meters
  • No testing at all

There is no common ground here either. The survey revealed the following practices:

  • On demand, which may originate from consumer or billing departments
  • As per sampling plan
  • Once a year for large consumers
  • No testing at all; the meters are replaced after a certain interval or when a complaint has been received
What are the objectives
  • To ensure the quality of the meter
  • To certify the accuracy class of the meter as per standard
  • As part of purchase agreement
  • To ensure functioning and features
  • To check the measurement accuracy
  • Quality control and inspection meters
  • To solve consumer complaints
  • To ensure proper functioning of meters
  • To evaluate the installed meter population
  • To form the basis for decision regarding replacement, maintenance or calibration

TESTING PRACTICES AND METHODS

By manufacturers

Manufacturers test the meters on large meter benches, because of the high volume of testing. They also use small single position test benches for R& D, quality control and inspection purposes. These test benches are based on the phantom load concept and are able to generate the desired test voltage, current, power factor, frequency and harmonics etc., as per international metering standards.

By utilities

Utilities generally use three types of equipment, depending on their testing policies.

  1. Large meter test benches, for testing large volumes of meters. This is prevalent in countries such as Hong Kong, Singapore, Israel, Thailand, Germany, Egypt, and India.
  2. Single position meter test benches for sample approval testing or random testing of small numbers of meters for batch approval.
  3. Portable meter testing equipment for on-site testing. Some utilities test the meter at real consumer loads (when only a reference meter is required) and some use the phantom load. Testing at consumer loads is a cheaper solution but has severe limitations, because the tester has to depend on the current load. Such testing does not give the tester much confidence in the results, however, and hence in most countries phantom load together with reference standards are used to test the meter thoroughly.

ON-SITE TESTING GAINING IMPORTANCE

The survey showed that on-site testing is gradually gaining in importance for the utilities around the world. There are several reasons for this.

  • Liberalization of utilities. (Governments are no longer willing to fund utility losses).
  • Growing consumer awareness.
  • For consumer satisfaction, in order to solve complaints immediately. This applies particularly in liberal and deregulated energy markets, where at a minimum large consumers can choose their energy supplier and can change supplier from one day to the next. Retaining existing customers is regarded as very important, and 83% of respondents gave high marks to this issue.
  • To reduce the cycle time and effort caused by removing the meter and testing it in a laboratory.
  • To provide statistical input for decisions regarding the replacement or continuation of the meter population, calibration and maintenance schedules.

TESTING INTERVALS

Name of country Interval Information  Remarks (additional information)  
Germany

Once every 16 years for electromechanical meters.
Once every 8 years for electronic meters.

If meters pass the test, both types will be reused for another four years.
When such testing is performed on a sample basis, the whole population of meters will be accepted if samples pass the acceptance criteria; if the sample meters do not pass the test, the whole population will be replaced.
Testing is generally performed in a laboratory  

Austria

Once every 20 years for electromechanical meters.
Once every 8 years for electronic meters.

If the meters pass, both types will be reused for another four years.
Testing is generally performed in a laboratory.

Denmark

Once every 16 years for electromechanical meters.
Once every 8 years for electronic meters.

If the meters pass, both types will be reused for another four years
India

Once a year for bulk consumers

Before installation  

On-site testing

  

Israel 2-8 years depending n metering mode, meter type and experience  Mainly labratory testing 
Hong Kong No planned testing   Meters are only tested on installation and for annual maintenance of meters for large customers 
Kenya Once a year for large customers  On-site testing 
Ukraine Once every 6 years   Also depends on meter type and the manufacturer 
Croatia No planned testing   
Colombia Varies from utility to utility    
Singapore Once a yera for large customers  On-site testing 
Thailand Once a year for large customers  On-site testing 
Russia

Once a year for large customers (in field conditions).

Once every 8 years in a labratory

100% of the billing meters should be tested, but this is not always achieved due to lack of infrastructure.

100% of the meters

Romania Once every 10 years  Labratory testing 

TESTING ON DEMAND

On-site testing is also performed on demand, either by a customer or by the billing department to investigate billing irregularities. This was confirmed by the responses to the survey, which revealed that these two issues received the highest marks and were given as the major reasons for on-site testing.

In some utilities, separate departments exist to respond to testing based on customer demand or to resolve billing issues.

ACCEPTANCE CRITERIA AND LIMITS

For labratory testing  As defined in IEC standards for respective class and type of meters, e.g. IEC 62052 - 11 & 62053 - part 11, 21, 22, 23 
For on-site testing No international standards exist for such testing.
Generally the same limit as defined for laboratory testing is used, although there may be some concessions for environmental influence. For example in Australia class 0.5 meters should be within 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. 

It is important to mention here that for on-site testing the use of the right equipment for the corresponding class of meter is essential. We learned that several utilities are not adequately equipped to perform this task efficiently. In some countries lower classes of equipment are being used to test high accuracy electronic meters, which prevents accurate decision-making regarding meter quality.

CHALLENGES IN METER TESTING

Rapid developments in metering technology have resulted in a greater challenge for utilities to test these meters in all respects.

  1. High precision electronic meters need high accuracy test equipment.
  2. The development of shunt-type meters – or the so called “closed link” meters, both single phase and three phase – cannot be tested with old meter test benches.
  3. Value-added functionality or features like PLC control, communication with IEC 1107, RS485 MBUS, pulse output etc. need special configuration of test benches.

REVENUE METERING – THE IGNORED COMPONENT

For large consumers, metering is done using instrument transformers (CT/VT). This means that instrument transformers are a very important part of revenue metering, but most of the utilities around the world do not test them, either before installation or during their lifetime. Utilities simply rely on the test certificates produced by the manufacturer. A few countries, such as Hong Kong, Singapore and Israel, do test instrument transformers.

CONCLUSION

All those who have a major interest in the accurate functioning of meters will be keen to test properly and regularly. Energy market liberalization has placed a high value on the metering components (both meter and instrument transformer) because of their direct link to revenue for the utility. Hence utilities need to keep pace with modern meter testing technology, and also ensure that the information generated or collected during regular testing – whether in a laboratory or on site – can be used for several purposes to save valuable dollars.

“Saving a dollar is better than earning a dollar”.