Survey of network impedance in the frequency range 2-9 kHz in public low voltage networks in AT/CH/CZ/GE

Setting realistic emission limits for distorting customer installations is a crucial requirement for a reliable and disturbance-free operation of public distribution networks. Therefore only an adequate share of the total allowable voltage distortion (compatibility level) has to be allocated to each customer installation. This allowable contribution of a single customer installation is usually small and difficult to assess. Hence, nowadays most standards and guidelines translate the allocated voltage distortion in a respective current distortion by using the network impedance at the considered frequency. As frequency-dependent network impedance is usually not known during the planning process, assumptions are required, which have to be realistic and not too conservative. This applies in particular to frequencies above 2 kHz, where the usually used extrapolation based on short circuit impedance can be very conservative due to the increasing impact of connected customer equipment on the network impedance. Based on a comprehensive measurement campaign in four different countries this paper identifies typical ranges of the frequency-dependent network impedance in the frequency range 2-9kHz. It analyses the impact of short circuit power and proposes a simplified impedance estimation, which can be used to calculate realistic current emission limits in the planning stage.