Switching Overvoltages in 60 kV reactor compensated cable grid due to resonance after disconnection

Some electrical distribution companies are nowadays replacing overhead lines with underground cables. These changes from overhead to underground cable provoke an increased reactive power production in the grid. To save circuit breakers the reactors needed for compensating this excessive reactive power could be directly connected to long cables. Switching both cable and reactor together will cause resonance to occur between the cable capacitance and the inductance of the cable during last end disconnection. Similar type of resonance condition is known to have caused switching overvoltages on the 400kV grid in Denmark. Therefore it is considered necessary to analyze further whether connecting a reactor directly to 60kV cable can cause switching overvoltages. A model in PSCAD was used to analyze which parameters can cause overvoltage. The switching resonance overvoltage was found to be caused by strong mutual couplings between the phases along with different resonance frequencies in the phases caused by unbalance in the grid. This is though not found to cause damaging overvoltages in a cable grid as in ENV-net's grid with the expected reactor values.