Robert Stiegler

Power quality disturbances caused by modern lighting equipment (CFL and LED)

The number of compact fluorescent lamps (CFL) and lamps based on Light Emitting Diodes (LED) increases continuously. Compared to the classical incandescent lamps the modern illumination equipment represents non-linear loads that may have impact on the Power Quality in low voltage grids. The network disturbances can be divided in two classes: continuous and transient disturbances. The paper presents the results of an analysis of three disturbance phenomena, namely low order harmonics, higher frequency emission and switch-on currents. Measurement results are presented for more than 150 lamps and possible impact on the grid is discussed with focus on the availability of respective standards. A large part of the analyzed data is organized in a Web-database (PANDA), which was recently developed by the authors as a platform for exchanging harmonic measurements of electronic equipment between laboratories all over the world.

Experimental-Based Evaluation of PV Inverter Harmonic and Interharmonic Distortion Due to Different Operating Conditions

This paper presents the results of comprehensive testing and subsequent detailed analysis of the obtained test results, evaluating harmonic and interharmonic performances of photovoltaic inverters (PVInvs) for a range of different operating conditions. The presented results indicate significant power-dependent changes in harmonic and interharmonic emissions of tested PVInvs for different supply voltage conditions (presence of voltage waveform distortions and various source impedance values). To correctly quantify and describe these changes in PVInv performance, this paper discusses and applies measurement procedures and metrics for evaluating harmonic and interharmonic emission recommended in existing standards, as well as some additional metrics and indicators. For some operating conditions, tested PVInvs significantly increase both harmonic and interharmonic emissions, and this paper also discusses the impact of PVInv control (e.g., maximum power point tracking control) as a possible origin of the interharmonic distortion.

Measurement of network harmonic impedance in presence of electronic equipment

Harmonic levels and their propagation in the power system are mainly determined by the network harmonic impedance. It is also an essential parameter for the calculation of harmonic current emission limits. Different methods for measuring the network harmonic impedance have been developed in the last decades, but all of them assume that the impedance is constant within a cycle at fundamental frequency, which is true in case of passive elements only. As nowadays most of the equipment in low voltage grids contains power electronics including rectifier circuits, network harmonic impedance will vary within a half cycle of power frequency. As more and more equipment operates with switching frequencies of several ten kHz, knowledge about the network harmonic impedance in the frequency range up to 150 kHz is also of significant importance. Based on a review of existing measurement methods, the paper presents an extended measurement method, which is able to address both, above mentioned issues. The application of the method is illustrated by two example measurements in different low voltage grids.

Portable measurement system for the frequency response of voltage transformers

Conventional inductive voltage transformers (VT) are widely used in MV, HV and EHV networks to measure harmonic voltages. Accuracy of VTs at frequencies other than nominal frequency (50Hz/60Hz) are not defined by standards, but may significant influence the overall accuracy of harmonic measurements. Thus a reliable compliance verification of compatibility levels, planning levels or emission limits (e.g. according to IEC 61000-2-12, 61000-3-6) may become difficult. Due to a lot of influencing factors (like manufacturing tolerances, burden or temperature) the frequency response varies more or less between different VTs. To achieve reliable results an onsite measurement of the frequency response is highly recommended. Nowadays the facilities for an accurate measurement of a VTs frequency response are limited to a few laboratories. The equipment is not portable in most cases. The paper describes the development of a first version of a portable measurement system for frequency responses of VTs for MV- and HV-networks. It is based on a widely used type of test generator together with especially developed software. The paper describes in detail the measurement method and discusses the accuracy limitations compared to the laboratory system.

Assessment of voltage instrument transformers accuracy for harmonic measurements in transmission systems

The measurement of harmonic and interharmonic voltages up to 2.5 kHz is an inherent part of the Power Quality assessment in electrical networks. In the past the monitoring of harmonic voltages has been of minor importance for many transmission system operators (TSO). As the number of power electronics connected to the transmission grid (e.g. self-commutating HVDC stations or converters in large wind power plants) increases continuously, the concern of TSOs regarding the harmonic levels grows as well. This is also confirmed by the recent significant increase of installed Power Quality monitors in transmission grids. In many cases the traditional voltage instrument transformers (VT), which are only designed to have a high accuracy at rated frequency, are used for voltage harmonic measurements. This questions the accuracy of the harmonic measurements and the reliability of any compliance assessment (e.g. against existing planning levels). The paper illustrates the challenges of harmonic voltage measurements from the viewpoint of the TSO. After a quick description of the initial situation the paper discusses two methodologies to measure the frequency response characteristic of VTs. The methods are applied to 10 VTs of two TSOs and the results are discussed with regard to the suitability of the VTs for voltage harmonic measurements.

Implementation of harmonic phase angle measurement for power quality instruments

This paper introduces a general implementation procedure for the measurement of harmonic phase angles using Power Quality (PQ) instruments. It is intended to fill this gap of the standards IEC 61000-4-7 and IEC 61000-4-30, particular with focus on grid measurements. While measurement for a single time instant is well defined, the paper focuses on methods to aggregate the harmonic phase angles in frequency and in time. The application of the methods is illustrated with different simulated and real data. Moreover, the accuracy of the harmonic phase angle measurement and procedures for implementation test are provided.

On Evaluation of Power Electronic Devices’ Efficiency for Nonsinusoidal Voltage Supply and Different Operating Powers

This paper analyses the impact of operating modes and nonideal power supply conditions on the efficiency of modern low-voltage power electronic devices. The sophisticated circuits and controls implemented in such devices are expected to result in increased efficiencies, higher operating power factors, and reduced harmonic emissions. However, the interactions of individual PE devices with the supplying network will impact exchanges of powers at fundamental system frequency and nonfundamental (i.e., harmonic) frequencies. This paper correlates the obtained results for harmonic performance and efficiencies over the entire range of operating powers of the considered PE devices using both standard definitions and some alternative interpretations.

Uncertainty Evaluation for the Impact of Measurement Accuracy on Power Quality Parameters

Power quality (PQ) analysis requires to calculate a lot of different parameters (e.g. unbalance, THD, harmonic powers, harmonic impedances, …) based on measured voltages and currents (fundamental and harmonics). Respective standards and data sheets of measurement equipment define the measurement accuracies only for these measured quantities. The resulting uncertainty of parameters derived from these measurement quantities are usually not available, but are crucial for a wide variety of applications, like the assessment of prevailing harmonic phasor or the fundamental negative sequence unbalance. This paper studies the influence of the accuracy of voltage and current measurements (fundamental and harmonics) on a set of PQ parameters that are derived from them. The analysis is performed in two ways: analytical (if possible) and probabilistic based on Monte Carlo simulations. Even if the different aspects of uncertainty propagation are known and has already been studied for several of the mentioned parameters, this paper is intended to provide a summary for a as complete as possible set of PQ-parameters taking also practical accuracy characteristics of todays PQ instruments into account. The paper finishes with a classification of the impact of the measurement accuracy on the resulting uncertainty of the discussed PQ parameters and indicates conditions where the calculated PQ parameters may suffer from insufficient accuracy.

Accuracy of voltage instrument transformers for harmonic measurements in elering's 330-kV-transmission network

The measurement of harmonic and interharmonic voltages up to 2.5 kHz is an inherent part of the Power Quality assessment in electrical networks. In the past the monitoring of harmonic voltages has been of minor importance for many transmission system operators (TSO). As the number of power electronics connected to the transmission grid (e.g. self-commutated HVDC stations or converters in large wind power plants) increases continuously, the concern of TSOs regarding the harmonic levels grows as well. This is also confirmed by the recent significant increase of installed Power Quality monitors in transmission grids [1]. In many cases the traditional voltage instrument transformers (VT), which are only designed to have a high accuracy at rated frequency, are used for voltage harmonic measurements. This questions the accuracy of the harmonic measurements and the reliability of any compliance assessment (e.g. against existing planning levels). The paper illustrates the challenges of harmonic voltage measurements from the viewpoint of a TSO. After a quick description of the initial situation the paper presents and discusses the measurements of the frequency response characteristic of different VTs and their impact on the accuracy of voltage harmonic measurements.