New demands on fully automatic test benches

Competition amongst the energy supply companies and the resulting new demands on the metering and accounting technology areas of the energy industry have lead in recent years to a constant flow of newer and more efficient electricity meters.

The manufacturers of testing technology for electricity meters are forced to adapt to these new functions and develop appropriate efficient testing systems and processes with which electricity meters can be rationally tested and accredited in accordance with national and international laws and regulations.

Fig 1:The Caltest 10 meter test bench

In addition to controlling the accuracy of electricity meters, which remains necessary, fully automatic test devices for meters will also have to fulfill a vast number of testing functions in the future, such as:

  • Testing of the meter reading (e.g. according to IEC 1107, via V24 interfaces or per modem).
  • Testing of the tariff functions (including the maximum and load utilisation profiles and the registers for the previous months).
  • Testing of meters with communication or control abilities via signals that are mixed on to the ground frequency (50Hz/60Hz).
  • Testing of meters with several pulse outputs (e.g. for active and reactive power) and with several pulse inputs (e.g. for other forms of energy such as heat, water or gas).

The German manufacturer of testing technology for electricity meters, HEG, has adapted to these new demands and has allowed the suggestions from leading energy supply companies to have an influence on the development of its new generation of fully automatic testing devices for electricity meters (Figure 1).

AUTOMATIC METER COMMUNICATION

Every test position of a 10-position test bench such as CALTEST 10 has a number of sockets which have been assigned different tasks within the framework of the testing process. (Figure 2). The sockets D0 (used to connect an infrared scanning head), CL0 (used to connect a double-wire communication connection) and if necessary RS 232 (used to connect meters with serial RS 232 interfaces) serve to communicate with the meter within the framework of the meter testing process.

Fig 2: Close-up view of the sockets

The communication abilities of the CALTEST meter test equipment offer the following advantages:

  • The information stored in the meter (e.g. owner number, serial number, year of manufacture) no longer needs to be manually entered into the software of the test equipment, but is read automatically.
  • The counter control of the maximum demand register and load profile register run fully automatically without the need for intervention on the part of the user of the facility.
  • The function of the communication interfaces is examined.

The Control-PC for test benches of the CALTEST type is fitted with so-called multi-serial interface technology. The read-out is time-saving and runs parallel (i.e. all meters are read concurrently).

RIPPLE CONTROL SIGNALS AND HARMONICS

Electricity meters whose tariff change-overs are controlled via signal technology that is modulated upon the 50Hz/60Hz energy supply network can be inspected with the CALTEST meter test equipment. This takes place within the framework of the counter testing of the electricity meter.

The test bench’s fully electronic test load generation function additionally allows one to generate circumstances under which the mains supply is disturbed. These possibilities will gain importance in the future should electricity meters equipped with functions for registering the quality of the network gain acceptance and if, under the circumstances, tariffs dependent upon the quality of the network are deployed in the competition between the energy supply companies.

Harmonics up to the 21st harmonic can be generated and measured as a standard measure. Enhancements of up to the 40th harmonic and even up to the 99th harmonic are possible with special models, as are voltage collapse and voltage drops from 10 ms duration.

DIGITAL ERROR INDICATORS

Digital error indicators are useful when carrying out the test (Figure 3) as they do not only indicate the actual error of the system being tested at the actual load point. Complex tests which require user-operation can be controlled and co-ordinated with the use of the indication technology. For example, messages such as "read counter stand" or "re-set scanning head" can be switched on to the error indicators. At the same time the error indicators can inform the user of the actual test being undertaken whilst testing, e.g. ‘automatic meter reading’. Any information whatso-ever can be integrated into the course of the examination by the user of the equipment.

Fig 3: The digital error indicator

WINDOWS NT SOFTWARE

Modern hardware for meter testing devices calls for forward-looking software operation and control. The operating systems Windows NT is excellently suitable for this purpose due to its multi-tasking abilities. The software of the CALTEST meter test equipment allows the user to easily integrate new types of electricity meters and testing programmes into the system’s database (Figure 4). In order to carry out a fully automatic meter test one can select the meter types to be tested and the test programme to be used.

Fig 4: Creation of a new meter type within the meter database

Following the test procedure, the results of the test can be printed out on the printer set up under Windows NT or transferred directly to Microsoft applications such as Word, Excel or Access.