Is there a need for a single-position test set in the lab?
Just a few years ago, it was standard practice for utility companies to have their own verification laboratories for the calibration of electricity meters. Experienced personnel in these labs had been completing complicated tasks connected with the testing and calibration of meters for decades. Because of their expertise these specialists also took responsibility for the installation and servicing of meters in the network. Now all utility companies are experiencing rising costs due to the liberalisation of the supply of energy. This means that ways of reducing expenses have to be considered.
Test laboratories are a major target for cost reduction. Small utility companies with a relatively low number of meters to service can find many reasons to close their own verification labs. On the one hand, sufficient investment has been made in the laboratories of some of the larger utilities to give them high productivity potential, enabling them to take over the tasks of others. On the other, there are independent laboratories which offer an overall service. Additionally international standards, such as the metrological guidelines of the European Union, allow the first verification of new meters by the manufacturer. There is, therefore, no need to calibrate new meters before installing them in a different European country.
The situation of some utility companies
Countries in the European Union have been experiencing a continuous reduction in the number of verification labs over several years. At the same time the number of specialists in the area of electricity metering is rapidly decreasing. Specialists with in-depth knowledge of modern electronic meters are rare in some utilities. As a result, such utilities are not able to fully utilise the advantages of electronic tariff meters. Their billing departments are not advised by technicians about the functions of installed meters and the functions with which new meters should be equipped.
As an example a four-quadrant meter with integrated load profile, internally controlled by a real-time clock, is able quite easily to give the same information which, in the past, was only available with a great deal of effort. It would have required a complete measurement set consisting of active power and reactive power meters including time switch. It is necessary to have accurate knowledge as well as experience to programme a multi-functional meter to be sure of receiving the required information, as the various energy and maximum demand tariffs have to be adjusted and released in the desired configuration. The personnel installing the meter at the consumer’s site must also connect it correctly. Manufacturers use different procedures to represent data on the display and position of the connections for input and output signals. The potential for making mistakes is quite high and can lead to significant errors in billing.
A suggested solution
Some utilities have decided to equip the department responsible for metering services with small test systems to overcome the problems described above. A modern multifunctional meter can be connected to this system and can be completely checked. Such a system is intended to acquaint staff with new models and scrutinise the precise configuration of a specific meter before it is installed.
Such a system is shown in figure 1. It consists of a three phase current and voltage source (phantom load) and a class 0.05 three-phase electronic reference standard integrated in the same cabinet. The main features are the extensive measuring ranges, high accuracy, and very low susceptibility to disturbance by external influences.
This instrument, the PTS 3.3, fulfils all requirements for control of the meter installation as well as analysis of the load parameters at the network point. It is also possible to use the PTS 3.3 in a stationary test system as well as a portable unit for on site meter testing.
Its advantages are:
- Easy verification of meters under precise load conditions, using the built-in, compact, current and voltage source
- Automatic operation using predefined load points without the need for an external PC
- Internal memory for storage of measurement results and customer data
- Displays of vector diagram and phase sequence for analysis of supply conditions
- User-friendly system for data input and operation of source and reference meter
- The system may be used either as a stand-alone reference standard meter, or together with the integrated power source.
The instrument provides the following functions:
- Independent generation of single or three phase current loading conditions for verification of meters using the incoming supply voltage
- Active, reactive and apparent energy measurement for three phase, 3 or 4-wire systems with integrated error calculator and pulse output
- Voltage measurement
- Current measurement directly or with clip-on CTs
- Power measurement per phase and combined phases
- Phase angle, power factor and frequency measurement.
The PTS 3.3 may be enhanced with several components to upgrade it for use as a PTS 3.3-2 single-position test system (Figure 2). In this case, it is installed on a meter test table. This table serves as a meter suspension rack that allows quick and easy mounting of the meter under test. A scanning head (type SH 2003) for testing of Ferraris or electronic meters is attached to a fixing device, allowing lateral adjustment. The scanning head is adjustable in depth and height as required to align with all normal configurations of meters. The measuring module, located in a channel underneath the suspension rack, serves as a meter error display and has inputs for output contact testing and a serial interface for tariff device communication.
The software package, CAMCAL for WINDOWS, is installed on the control PC of this single-position test system enabling automatic testing of complex meters. It also allows the reading out of various tariff registers of the meter under test and evaluation of their content.
The single-position system described above can also be used in accredited laboratories. The ranges of current, voltage, phase displacement and frequency allow generation of all values prescribed by international rules for the verification of meters. The accuracy of the integrated reference standard, 0.05 %, is sufficient for verification of meters up to class 0.2S.
Laboratories equipped with productive automatic meter test benches often verify large batches of meters over more than one shift. It may not be possible to interrupt the normal process for a special test on a single meter, especially where testing and verification of multifunctional meters takes a considerable amount of time. In such instances use of the single-position system described above will increase the efficiency of the verification lab and will lead to significant cost savings.