A reliable energy supply has meanwhile become an important location factor for many companies. While power failures and voltage fluctuations were among the most important parameters of supply quality in the past, voltage transients and voltage harmonics are becoming more and more important. This is mainly due to the increasing number of non-linear loads and many decentral renewable energy sources. In order to guarantee uniform standards for electrical energy supply in Europe, the minimum requirements for voltage quality are defined in a European standard. This is EN 50160, which is entitled “Voltage Characteristics in Public Distribution Systems”. This standard is to be understood as a product standard for electrical energy and for this reason is also used as a valid product standard in electricity supply contracts. In February 2014 the Federal Court of Justice in Germany made it unequivocally clear that electricity is also subject to the Product Liability Act. The distribution network operator is thus liable for damage to electrical consumers that can be traced back to poor voltage quality on the part of the distribution network operator. For this reason, many measuring device manufacturers now offer measuring devices that prepare automated quality reports in accordance with EN 50160. Digital billing meters are also increasingly offering power quality functions in accordance with EN 50160. While the measuring devices can process the voltage directly in the low voltage range, we rely on voltage transformers or voltage sensors in the medium and high voltage range. The voltage quality is usually measured on older already existing systems. However, the built-in voltage transformers usually do not give any indication of the transmission behavior at higher frequencies on the rating plate. The devices are only specified for the 50 Hz fundamental frequency of the network. However, measurements according to EN 50160 require a frequency range of up to 2 kHz. We want to investigate the question of whether the existing devices are suitable for measurements up to 2 kHz.

A resonance point can be seen at approx. 6 kHz. While the voltage transformer transmits the primary signal acceptably up to approx. 5 kHz, an amplitude error of approx. 100% and a phase error of 87 ° results at approx. 6 kHz. For example, a reliable PQ analysis up to 9 kHz can therefore not be carried out with this voltage transformer.

Despite the normatively regulated voltage levels, every instrument transformer manufacturer has a large number of different voltage transformers with different primary coils in order to be able to meet the most diverse secondary configurations by the customer. These voltage transformers have already been delivered and installed in measuring fields. The manufacturer can only carry out a rough calculation of the first resonance point in connection with the archived production documents. However, the resonance point measured in practice can often deviate from the calculation result by a few kHz. It is therefore very difficult for instrument transformer manufacturers to make reliable statements for devices that have already been delivered.

Authors:

Roland Buerger (MBS AG)
Business Development/R & D, MBS AG, Sulzbach-Laufen (Germany)

https://www.linkedin.com/in/roland-bürger-83b817148/

rbuerger@mbs-ag.com

Dipl.-Ing., Bernhard Grasel
Sales Manager, NEO Messtechnik, Zoebern (Austria)

https://www.linkedin.com/in/bernhard-grasel/

bernhard.grasel@neo-messtechnik.com

Where can I get more information?

Your NEO Messtechnik Experts

• LinkedIn
• YouTube