For lightning transient studies, the line insulators are represented by voltage-dependent switches. There are different options to model the flashover during lightning transients, such as:

• Voltage threshold: 
  • The flashover is based on a constant threshold value
  • The voltage dependent switch is closed if the voltage across the switch exceeds the threshold
  • The flashover voltage is independent of the waveform and duration of the overvoltage
• Volt-Time Curve:
  • The flashover is based on a non-linear volt-time characteristic
  • The volt-time characteristic represents the dielectric strength of the line insulator during the transient as a function of time
  • The voltage dependent switch is closed if the voltage across the switch exceeds the volt-time curve
  • The flashover voltage is a function ofovervoltage magnitude and time duration of the overvoltage. Thus, the waveform is considered
• Leader Progression Model (LPM):
  • The flashover is based on a physical model of the leader
  • The leader propagation is modeled based on the voltage difference across the insulator
  • The voltage dependent switch is closed if the leader length exceeds the length of the line insulator
  • The flashover voltage is a function ofovervoltage magnitude and time duration of the overvoltage. Thus, the waveform is considered

Detailed information about the different flashover models and transmission line insulators in general can be found in the Application Example "Lightning Transients" that is available in the PowerFactory examples.

The three different models are presented and compared in the attached *.pfd project.