GPS-synchronized harmonic measurements performed on a 400kV transmission network Wojciech Wiechowski, Jan Lykkegaard Birgitte Bak-Jensen, Claus Leth Bak Jacek Wasilewski Planning and Transmission dept. Inst. of Energy Technology Inst. of Electrical Power Engineering Energinet.dk (TSO) Aalborg University Warsaw University of Technology Fredericia, Denmark Aalborg, Denmark Warsaw, Poland wwi@energinet.dk , jly@energinet.dk bbj@iet.aau.dk , clb@iet.aau.dk jacek.wasilewski@ien.pw.edu.pl Abstract—In this paper, GPS-synchronized harmonic measurements performed on the transmission network of the Danish TSO Energinet.dk are presented. The purpose of the measurements was to verify a computer model of the network. The selected verification method was based on determination of transfer harmonic impedance by switching a series component that contains a shunt branch [1], [2]. Harmonic currents and voltages were simultaneously measured at three 400kV substations with OMICRON CMC256 units with EnerLyzer function and GPS synchronization units. Time domain “snap- shot” measurements of three-phase voltages and currents were synchronously taken, while a power line was switched out and in, and the results were post-processed in Matlab. Harmonic voltages were measured using capacitive taps of the 400kV/150kV autotransformer bushings. Harmonic currents were measured as voltage drop on low-inductance resistors inserted in series with the metering equipment. Due to largely unbalanced harmonic currents, the computer network model was verified by a modified verification method, based on injection of measured harmonic currents and comparison of resultant voltage increments. The method requires precise synchronization of the units and sufficient level of harmonic distortion in the network. Keywords- bus impedance matrix; global positioning system; harmonic analysis; impedance matrix; impedance measurement; time domain measurements; power system harmonics. I. INTRODUCTION Computer simulation model of the Danish transmission network created in the DIgSILENT PowerFactory software was adapted to be used for harmonic analysis for frequencies up to 2,5kHz [1]. Before the usage, the model shall have had to be validated by real-world harmonic measurements. In order to eliminate the effects of background harmonic distortion, an incremental method was chosen. Preliminary simulations have shown that the highest harmonic increments can be obtained by switching one of the transmission lines. No such method of verification of a harmonic model by switching a linear series element was found in the literature. Therefore, two such verification methods based on calculation of transfer harmonic impedance were developed and are described in [2]. One of them allows that series element contains a shunt impedance, such as it is in case of a transmission line. When such a line is disconnected at one end, the transfer harmonic impedance of the network can be then calculated from harmonic currents and voltages that are measured before and after line disconnection. In this paper, the required by the method harmonic measurements are described. The measured harmonic currents occurred to be largely unbalanced, and therefore, an alternative method has been also developed. This method and the verification of the computer model are presented in this paper. II. LOCATION OF THE MEASUREMENTS Due to modifications of the 400kV network, two power lines located between 400kV substations NVV5 and FER5 were temporarily operated in parallel. One of the lines could be disconnected and reconnected at one end. At both ends of the line harmonic voltages and harmonic currents were synchronously measured using GPS-synchronized OMICRON CMC256 units with the EnerLyzer function. In addition, measuring equipment was also installed at a third substation, Tjele. Location of the three substations is shown in Fig. 1 and a schematic diagram of the network section is shown in Fig. 2.