Matthias Klatt

Frequency Responses of MV voltage transformers in the range of 50 Hz to 10 kHz

Voltage quality plays an important role in modern distribution networks. One voltage quality parameter is harmonic distortion. Voltage harmonics in MV-networks are measured in most cases by using installed inductive voltage transformers (IVT). The accuracy of these transformers for frequencies above nominal frequency (50Hz or 60Hz) is usually not known. The paper presents a systematic analysis of the frequency-dependent accuracy of these IVTs for harmonic measurements in the frequency range up to 10 kHz and its dependency from different factors and operating conditions. After an overview of possible factors that influence the frequency response, the used measurement equipment and methodology is described. The frequency responses of more than 85 IVTs with rated primary voltages between 10 kV and 35 kV were measured and analysed. The significance of each influencing factor to the frequency response is discussed and finally a frequency-dependent measurement uncertainty range for 20 kV IVTs is proposed.

Future work on harmonics - some expert opinions Part II - supraharmonics, standards and measurements

A workshop on power system harmonics was organized in Stockholm in January 2014. On the agenda was among others a discussion on what are the main issues on harmonics at the moment and in the near future. Some of the issues discussed at that workshop are presented in this paper and its companion paper. In this paper the following issues will be addressed: the appearance of emission at higher frequencies (supraharmonics); the need for new and improved standards; measurement issues and data analysis.

Future work on harmonics - some expert opinions Part I - wind and solar power

A workshop on power system harmonics was organized in Stockholm in January 2014. On the agenda was among others a discussion on what are the main issues on harmonics at the moment and in the near future. The results of this discussion are summarized in this paper and some of the issues are discussed in more detail in this paper and in its companion paper. This paper discusses emission from wind and solar power as well as advantages and disadvantages of active and passive filters.

Power quality challenges in future distribution networks

Power quality in distribution grids is determined by consumer topology, generation topology, network topology and other non-electrical, environmental influences (i.e. weather). New developments in all mentioned characteristics, e.g. micro generation or e-mobility lead to significant changes in the grids and the equipment connected thereto. This paper discusses possible impacts of new technologies on power quality and is intended to attract attention of all stakeholders to these issues. Another aspect is the increasing use of smart meter technology in distribution networks. Integrating Power Quality functions into smart meters can help to manage Power Quality in future grids more efficient. The second part of the paper outlines several aspects that have to be considered to ensure that the integration becomes economical and reasonable.

Comparison of measurement methods for the frequency range of 2 kHz to 150 kHz

The accurate and comparable measurement of voltages and currents in the frequency range of 2 kHz to 150 kHz is a basic requirement for the assessment of emission limits, compatibility levels and immunity limits and therefore important for a consistent standardization framework. Currently a measurement method for frequencies of 2 kHz to 9 kHz exists in the informative annex of IEC 61000-4-7, which could be extended in application to 150 kHz. The committee draft for vote of IEC 61000-4-30 Ed.3 proposes a new method for the frequency range of 9 kHz to 150 kHz, which is different from the aforementioned one. This paper identifies parameters with impact on measurement results and compares both methods based on multiple test signals, which are derived from lab measurements of different equipment and field measurements in low voltage networks. The comparison is carried out regarding the necessity of filters, chosen bandwidth, impact of band boundaries and methods for aggregation in time. The results show that the two measurement methods have individual benefits and drawbacks. Finally, the paper proposes several approaches to combine the advantages of both methods.

Filter for the measurement of supraharmonics in public low voltage networks

The increase of voltage and current distortion as well as interferences in the frequency range of 2 kHz to 150 kHz due to technologies like power line communication or self-commutating converters have led to the urgent need for electromagnetic compatibility (EMC) standards in this frequency range. Measuring compatibility levels or test compliance with limits for emission and immunity requires accurate, reliable and reproducible measurement methods. A major prerequisite for accurate measurements in this frequency range are suitable high-pass filters to reduce the fundamental component and its harmonics below 2 kHz in the measurement signal. This paper shortly reviews the filter proposals in present standards and proposes an alternative infinite impulse response (IIR) filter design, which is optimized to have a minimum number of poles, a high damping of the fundamental and a high accuracy above 2 kHz. The resulting transfer function of the new filter is provided. Based on the general design, an analog and a digital implementation are derived. The advantages and drawbacks of both implementations are discussed. Furthermore, the paper describes in detail the prototype of an analog filter implementation, which consists only of passive elements (no electronics) to improve the signal-to-noise ratio (SNR) of a measurement system. The accuracy and damping behavior of the filter is presented, which shows good overall performance. For the digital filter implementation structure and parameters are given for 106 samples per second. Finally, the application of the analog and the digital filter is illustrated by laboratory measurement. It shows only marginal differences between both implementations. However, a gain between 5 dB and 10 dB in SNR is achieved by the analog implementation compared to the digital one.

On the interharmonic emission of PV inverters under different operating conditions

This paper presents the results of experimental evaluation of interharmonics produced by PV inverters (PVInv) for a range of different operating conditions. First, intrinsic interharmonic generation due to Maximum Power Point Tracking (MPPT) control is analyzed. Afterwards, generation of current interharmonics assessment is analyzed adopting the IEC 61000-4-7 sub-group concept and their effects on the supply voltage are evaluated in terms of short-term flicker index, Pst. Finally, the paper investigates interharmonic currents produced by PVInvs when harmonics and interharmonics are superimposed to the fundamental supply voltage.