How to Choose the Right Meter Test Equipment

Abstract

Poorly specified requirement for purchasing the meter test equipment does not help the decision maker to select the right equipment for right application. In most of cases final decision maker has little or no information on the importance of meter test equipment and how small issue could play a big role in overall testing. Meter testing activity is considered as the last and low priority activity until they dive into this sea.

This paper explains the systematic approach in selection of meter test equipment and will help to reduce the overall cost in a short term and long term.

Process to choose the right product

Steps mentioned in the flow diagram will assist to reach the right selection of test equipment.

Figure 1: Process to choose the right equipment.

Identify the objective

Various organizations, based on their meter testing objective can be broadly categorized as follows.

Identify the objective

Various organizations, based on their meter testing objective can be broadly categorized as follows.

Table 1: Type of Organisation and their requirements

Different objective of meter testing leads to direction of major group of meter test equipment.

Table 2:Define objectives and selection of meter test equipment

Location of testing

Category of meter testing can be divided mainly into two categories. One is suitable for testing in laboratory and another is suitable for onsite testing. Onsite test equipment should be lightweight equipment.

On site testing is done by two different methods: –

1. Using existing load: In this method, reference meter are connected in series with meter under test and perform the testing on the existing loads. In this situation tester has no influence on the fluctuations of test parameter like voltage, current power factor and frequency etc. This kind of methods only provide the approximation of accuracy of meters and basis of decision making whether the meter need to be removed and tested in laboratory or not. This kind of testing can’t use for legal or to resolve the dispute.
2. Using Phantom Load: In this method, meter under test is removed from existing load and external supply (test parameters) fed via portable phantom loads. Reference meter is connected in the series with meter under test. This kind of testing is very popular in Scandinavian countries, Europe, Hong Kong. This testing is very close simulation of laboratory testing, hence used for legal purpose also.

Quantities of meters to be tested

It is important for bulk meter tester that test equipment is: –

• Able to perform automatic testing and required less manual intervention
• Able to do several tests on single bench e.g. Calibration/adjustment, starting and creep, register test, other functional test or if need to perform on the several bench then flow of meters should be minimized or in such a way that total test time can be optimize. For example Gantry system is quite suitable for bulk meter tester, use of quick connector to reduce the loading and unloading time
• Can be integrated in to production process, so that records, data administration can be more simple and integrated into the common network. Statistical information should be readily available.

It is recommended to pay attention on the production flow process, time required by each activity and total time require in one lot of tested meter.

If equipment is going to use simply for routine testing, then features related to type testing such as Harmonic generation, frequency variation etc become less significant.

Small quantity testers are generally research laboratories of a manufacturer or test house or OEMs, that tests several different kinds of meters; hence test equipment for such user should be able to perform special tests or type tests like 3^rd, 5^th and other higher harmonics, frequency, and other influence quantity tests.

Meter technology and testing methods

Mainly Accuracy of meters is tested by sensing of rotor mark in electromechanical meter and LED blinking in Electronic meter. These kinds of testing need sensing device, which should be able to sense both (rotor mark as well LED blinking). Sensing device or so-called “Scanning head” should be able to sense the optic pulse; criteria of such pulses are defined in IEC 62052-11 clause 5.11.1 and 5.11.2. Some meters also give electrical pulse output as defined in IEC 62053-31 and to test these pulses will require an additional compatible adopter according to output type A or B.

Table 3 : Meter technology and testing methods

Test to be performed

The tests which need to be performed by different user group vary due to difference in their meter testing objectives. This information guides you on essential and non-essential feature of test equipment. For example equipment used for routine testing doesn’t need to have harmonic (3^rd, 5^th, sub, odd & even) generation and other type testing features.

Table 4: Test to be performed

Regulatory requirements

Although each country has its own regulatory requirements, which are drawn from, national or international standards but in general following factor influences the decision of meter test equipment.

• Accuracy class of meter under test
• Accuracy requirements of meter test equipment
• Routine, acceptance and type test requirements

It is recommended to use high precision measuring equipment to cover all kind of accuracy class meters economically, and this serve following other purpose

• To avoid high amount of errors in measurement and achieve best measurement uncertainty.
• To boost up the confidence in measurements and avoid conflicts and dissatisfaction arising due to high error and influencing parameters like voltage, current, frequency, temperature and harmonics etc. Influence of these parameters on accuracy of high precision equipment is very low.

Automatic meter test benches are better fitted into the other regulatory requirements as defined in the international standard IEC 62052-11

Table 5:Accuracy class of meter V/s Accuracy of meter test equipment

User needs to review the available type meter on network and also consider future trends in meter technology, then decide about the accuracy and other parameters of meter test equipment

Final steps of the process

After completion of study, user needs to make market search on the available equipment, solutions, understanding the features & functions of the new technologies, cost involvement and upgradeability for future.

Finally define your technical requirement and proceed for purchase action.

Analyze the available offers in details or go for demonstration to answer your queries.

In Europe, it is quite common to discuss very concrete and in detailed, information on the type of meter and how test will be performed. Technical information on meter type can be given to supplier, so that tester gets very concrete and clear answer on possibilities from test equipment suppliers.

Important consideration for Meter test equipment

Here mentioned few tips can be helpful to define the specification of meter test equipment. Product category mentioned here is most preferred, by different user groups.

Single position test bench

• Capable to test following meters,
  • Single phase active, reactive, open link and closed link
  • Three phase 3 wire or 4 wire active, reactive and apparent meter
  • Three phase closed link meters direct connected meters
  • Testing of substandard meters of class 0.05 or 0.1 or 0.2
• Capable to perform following tests
  • Pre-warming
  • Accuracy test
  • Starting current
  • Creep test
  • Dial test/register test
  • Influence quantity test
    • Voltage
    • Frequency
    • Harmonics (even and odd as mentioned in IEC 62053)
    • Reverse phase sequence
    • Voltage unbalance
    • Influence of self-heating
  • Repeatability test
  • Other test, if any (please furnish the clear details of such tests)
• Electrical characteristics
  • Range of Voltage generation e.g. 40..300 V phase – Neutral (Minimum 20 VA per phase power rating)
  • Range of current generation e.g. 1mA to 100 phase – neutral (Minimum 60 VA per phase power rating)
  • Distortion of waveform for voltage and current both < 0.5%
  • DC content in the voltage and current circuit should be as per IEC 62057-1
  • Setting accuracy should better than 0.05% of the range
  • Protection of circuit against overload, short circuit/open circuit
  • Scanning head capability to scan the rotor mark and LED blinking as defined in IEC standards 62053-11 clause 5.11.1 &2. Accuracy of scanning head should be higher.
• Software requirements, e.g.
  • Capable to perform manual testing
  • Automatic testing
  • Creation of meter related tables (type tables) and test sequences
  • Storage, printing and administration of results

Multi position test bench

Apart from general technical requirements and features mentioned above, following characteristics need to be specially taken care.

• Sufficient power (VA Rating) to drive the maximum current rating with given meter connection style or art, considering electromechanical and electronic meters. If quick connectors are to be used then additional power will be required.
• How the meter will be connected. For bulk meter tester, it is recommended to pay attention on time consumed in each meter connection. Specific design of quick connection can help to reduce the testing time.
• Quality of quick connector is a crucial for the generation unit. Because low quality and high amount of iron in the spring will create high resistance and can distort the waveform. Hence it is better to use silver tip on quick connector, strong spring and special spring to minimize the distortion due electromagnetic induction effect.
• How many task or tests performed on the bench. Avoid frequent loading and unloading of meters. Multitasking will improve the utilization factor of the test bench.
• If meters need to be communicated, then make sure that the hardware, software and protocol supports the communication
• How traceability with national metrological institute will be maintained, if user has numbers of test benches.
• Testing of closed link meters (single or three phase). It is recommended to take decision along with basic test bench. Now a days number of closed link meters are growing due to new ICT, which don’t have isolation between, voltage and current circuit and also some electricity decided to closed permanently to reduce the tampering possibilities. If ICTs are required then power rating of the amplifier should be sufficient to drive current along with ICT. For example in this case 10 position test bench with ICT will need 1000 VA per phase.
• Scanning head capability to scan the rotor mark and LED blinking as defined in IEC standards 62053-11 clause 5.11.1 &2. Accuracy of scanning head should be higher.

Portable meter test equipment

Portable meter test equipment comprises reference meter and electronic source to generate the test parameters and conduct the testing. Below mentioned few points are important to consider while selecting the testing.

• Possible to automatic test to conduct the accuracy tests as mentioned in the applicable national and international standards.
• Low influence with external quantities like temperature, humidity, frequency, voltage, harmonics. This will help to achieve the best measurement uncertainty during onsite testing.
• Sufficient VA rating (for portable phantom load): – For onsite testing, needs bit longer cables, hence portable sources should be.
• Scanning head capability to scan the rotor mark and LED blinking as defined in IEC standards 62053-11 clause 5.11.1 &2. Accuracy of scanning head should be higher.
• Other features like connection check, generation and measurement of harmonics

Conclusion

Metering technology is changing at faster speed. To cope with this speed needs extra care in selection of meter test equipment, particularly test bench. Adequate information on meters and their technology, test to be performed & methodology, metrology involved in the testing and available meter test equipment technology will help tester to choose the right equipment which can meet not only present requirements but futuristic also.

If electronic meters are need to be tested using IEC 62056 communication, please mentioned the details of such requirement.

Although metering standard defined 10VA per phase for normal electronic meter, but in case of additional accessories in the meter, addition VA may be allowed. Current drawn by the SMPS power supply of some electronic meter can distort the waveform quality and this could affect the overall measurement uncertainty of test system.

Total resistance of current circuit which include cable, contact type and resistance of current circuit of meter is the key factor in deciding the total VA rating of current circuit of the source.

Traceability is a unbroken chain of measurement relationship between national standard and standards used in test system

In direct connected meters, a link between voltage and current circuit, which cannot be open during testing. To test such meter needs single phase multi-secondary voltage transformer (MSVT) for single phase meters, and isolating current transformer (ICT) for testing of three phase meters. The test bench, which has ICT, is capable to test single phase closed link meters.