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The insulation strength of an EHV transmission line is mainly governed by

  • The insulation strength of an EHV transmission line is mainly governed by Switching overvoltage.
  • Switching overvoltage is a type of transient overvoltage that occurs when a circuit breaker or switch is opened or closed, causing a sudden change in the current through the circuit.
  • This sudden change in current can cause a rapid change in the voltage across the circuit, which can result in overvoltage stress on the insulation.
  • The magnitude of the switching overvoltage depends on various factors, including the rate of change of current, the inductance and capacitance of the circuit, and the power system frequency.
  • For EHV transmission lines, which operate at voltages above 345 kV, the magnitude of the switching overvoltage can be very high, and it can pose a significant risk to the insulation of the line.
  • To protect against switching overvoltage, various measures can be taken, including the use of surge arresters, which are devices that limit the amplitude and duration of overvoltages by providing a low-impedance path for the surge current to flow.
  • In addition, the insulation of the transmission line itself can be designed to withstand high levels of overvoltage stress, by using materials with high dielectric strength and by providing adequate insulation spacing.