HV AC Switchgear

Voltage shapes for switchgears in grid according to IEC

The voltages and the overvoltages that stress the insulation shall be determined in amplitude,shape and duration.
For maximum value overvoltage of the various classes shall be:

  • For the continuous power-frequency voltage: a power-frequency voltage with r.m.s. value equal to the highest voltage of the system, and with duration corresponding to the lifetime of the equipment.
  • For the temporary overvoltage: a standard power-frequency short-duration voltage with an r.m.s. value equal to the assumed max of the temporary overvoltages divided by √2
  • For the slow-front overvoltage: a standard switching impulse with peak value equal to the peak value of the assumed max of the slow-front overvoltages.
  • For the fast-front overvoltage: a standard lightning impulse with peak value equal to the peak value of the assumed maximum of the fast-front overvoltages phase to earth.
  • For the very-fast-front overvoltage: the characteristics for this class of overvoltage are specified in relevant standards.
  • For the slow-front phase-to-phase overvoltage: a standard combined switching impulse with peak value equal to the peak value of the assumed maximum of the slow-front phase to phase overvoltages .
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