Application of Point-on-Wave for Controlled Switching of Capacitor Banks and Cable Circuits in the Dutch 150 kV Transmission Grid
Evaluation of the Effectiveness of Point-on-Wave and the Impact of Circuit Breaker Imperfections
M.C. Hoogendoorn (TU Delft - Electrical Engineering, Mathematics and Computer Science)
M. Popov – Mentor (TU Delft - Intelligent Electrical Power Grids)
K. Velitsikakis – Mentor (TenneT TSO B.V.)
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Abstract
In recent years, the electricity grid has evolved rapidly due to the large-scale integration of renewable energy sources and the growing demand for electricity. This development has led to more customer connections and grid expansion projects, resulting in a more dynamic and flexible system. To maintain safe and stable grid operation, frequent switching of equipment, such as reactive power compensation devices (e.g., capacitor banks) and cable circuits, is often required.
However, energising capacitor banks and cable circuits can cause severe voltage transients and inrush currents. Such transients could impose challenges such as dielectrically stressing the insulation of power apparatus and violating Grid Code limits related to Power Quality. Point-on-Wave (PoW) switching is a promising technique to suppress these unwanted effects, but its practical effectiveness is not yet fully understood by TenneT, the Dutch transmission system operator.
This study investigates the effectiveness of PoW switching for energising cable circuits and capacitor banks in a Dutch 150 kV grid scenario. It also examines how switching imperfections, such as “pole scatter” and an imperfect “Rate of Decrease of Dielectric Strength”, affect the PoW switching effectiveness. The central research question is: “Is PoW switching an effective solution for meeting the TenneT NL policy requirements when switching capacitor banks and cable circuits?”
To answer this research question, a state-of-the-art analysis is first carried out to provide the technical background of PoW switching. Next, TenneT’s current policy on PoW implementation and the voltage quality requirements of the grid are reviewed to assess whether the outcomes of this study align with these standards. Based on this foundation, a detailed simulation plan is developed, and the simulation results are analysed. Finally, a discussion section offers a critical reflection on various aspects, including alternative mitigation methods, the alignment of statistical and deterministic data, and the need for mathematical compensation of external variables.
It can be concluded that Point-on-Wave (PoW) switching significantly reduces inrush currents and transient overvoltages compared to switching without PoW. Based on 200 Monte Carlo simulations per configuration, it is shown that without PoW, all simulated capacitor banks and cable circuits exhibit Rapid Voltage Changes (RVC) exceeding the 10% limit set by TenneT’s policy. However, when PoW is applied, none of the investigated capacitor banks, rated at 25 MVAr, 50 MVAr, and 75 MVAr, nor any of the simulated cables up to 49.5 km in length exceed the 5% RVC limit specified in the grid code, whereas without PoW, these configurations do show a significant amount of exceedances above this 5% limit.