By Detlef Ebel and Peter Kurth
Economic pressures related to the installation and checking of metering devices may lead to incorrect metering installations, which in turn can result in considerable financial losses.
A metering installation in a low voltage network up to 1,000 V consists of energy meters, current transformers and possibly auxiliary equipment. A metering installation in medium voltage, high voltage and ultra-high voltage networks is made up of energy meters, current (CT) and voltage (VT) transformers and possibly auxiliary equipment.
This article describes what may occur using a typical installation in Germany as an example. However, it is safe to assume that the same may be said for installations all over the world.
In a low voltage metering installation with CTs (Figure 1), the service technician may unintentionally introduce various errors, such as changing polarity in one current phase, asymmetrically connecting the voltage phase, or incorrectly connecting the neutral wire, etc.
Incorrect connections such as these will result in measurement errors and therefore incorrect bills. Depending on the kind of incorrect connection, the customer bill may be too low (loss for the utility) or alternatively the result can be a positive error (the customer would pay too much). In this magazine several articles have been published in recent years related to this topic1, 2. However, all too often such articles do not draw any conclusions.
During numerous meetings the engineers from EMH Energie-Messtechnik GmbH have discussed the problem of incorrectly connected metering installations with customers from Germany and around the world. The outcome of these was to develop a corresponding training course focussing on this very point. Since 2004, EMH has regularly conducted two-day training courses for technicians and engineers from German utilities. To make the training as realistic as possible, EMH has metering installation cabinets (as per the standards used by German utilities) in the training room at its training centre. A part of the extensive training topic list includes:
- Connecting measuring devices for checking the metering installation
- Determining errors and checking connections on-site – theory and practical exercises
- Instrument transformer testing and burden measurement on-site – theory and practical exercises.
An example of an installation with changed polarity in current phase L2 together with the connected reference meter is shown in Figure 2.
In this example what would the measurement error be? And how much energy would the meter register? At balanced load, the meter in this case registers only one-third of the consumed energy, i.e. a two-thirds loss for the utility. This incorrect connection may occur in a high voltage or ultra-high voltage network. The mounting financial losses that may occur if this mistake is not discovered quickly may readily be imagined!
What options do we have to find this fault? After connecting a portable measuring device as shown in Figure 2, the operator on-site has the facility to recognise the nature of the incorrect connection using graphical displays or the display of measured results (Figures 3, 4).
The measured values marked red in Figure 3 indicate the changed polarity in current phase L2. Likewise, the display of the vector diagram also highlights the incorrect connection. The graphical display in Figure 4 instantly indicates the polarity failure in current phase L2 and at the same time shows that the rotating field in the voltage is correct.
Many other examples of incorrect metering connections could be shown; however, suffice to say that the EMH user seminars provide a high level of detailed information and pass on sufficient knowledge and practical training for the participants to use in every day practice, thereby reducing the utility’s so called non-technical losses. The seminars take place in a state-of-the-art training centre six to eight times per year, each with 15 to 20 participants. Qualified members of the after sales service department, who have more than 10 years experience in the field of problems and applications of measuring technology in electrical networks, bring a high level of experience and guide the participants through the seminar,
The participants regularly report after the seminars that the information gained has helped them immensely in their understanding of metrological practices, while also providing useful tips and hints to discover circuit errors and thereby reduce possible utility revenue losses.
The seminar and the comprehensive documentation themselves often help to justify the implementation of on-site tests and the use of portable measuring device for those tests. It is recognised that faulty installations can be discovered and thereafter the energy billing can be corrected. Hence, the asset costs return (payback) can be achieved within a very short time.
It is not the goal of this review to explain the full content of a two-day seminar. The above examples show how the seminar is run, and how the participants are led to a practical and theoretical understanding of the issues they face regularly on-site. Besides these aforementioned topics, some further focuses of the seminar include:
- Presentation of different kinds of measuring devices, design of installations, international and national standards, and explanation of different kinds of meter and instrument transformer connections.
- Analysis as to why it makes sense to check the overall installation after installing a new metering device and the recommended time intervals for follow up tests. Also demonstrated are the kinds of errors that may occur when installing metering devices and the possible errors during the operational life of metering devices.
- Presentation of measuring devices by means of which the errors described above can easily be discovered. The participants work with such metering devices later on in the practical sessions. Examples of destroyed measuring devices and installations show the consequences of wrong connections. Using these examples participants are encouraged to work on-site with the required accuracy and patience, otherwise it may be not only the metering devices that are destroyed, but also life may be endangered.
- Connection of the measuring devices to the installation in different kinds of connections (three wire, four wire, direct connection, connection over voltage and/or current transformers, etc.) and errors in the connection that may occur, in particular in the case of using current clamps.
- Test of instrument transformers on-site, in particular current transformers, and measurement of the operating burden3. Within this topic, participants also perform practical exercises and discover for themselves the consequences that incorrect burdening has on accurate recording of energy consumption.
- The possible errors in installations are explained in detail, as well as their influence on the energy registration of the meter. Approximately ten different cases of faulty installations and how they can easily be discovered using portable test equipment are explained.
The highlight for all participants in any seminar is the practical application tests. By using the knowledge gained the participants have to discover and correct errors in the metering installation themselves.
As the cost of energy increases, the reduction of nontechnical losses gains greater importance within utilities. For more information on the topics described, the authors are willing to provide the results of their experiences in this area.
- Metering International Issue 1 1999, page 31. Discovering circuit errors in meter in-stallations by Franz Baumeler and Detlef Ebel.
- Metering International Issue 3 2001, page 46. New developments in meter testing: Total meter quality management by Herbert Odermatt.
- Metering International Issue 3 2006, page 76. The instrument transformer – a racecar with the wrong settings? by Detlef Ebel, Gösta Hallgren and Peter Kurth.