ZnO lighting arrester
QuickField simulation example
This is an example of the ZnO arrester simulation, performed with QuickField software. The arrester consists of ZnO tablet placed inside ceramic tube. Electrodes are connected to the end tablets.
Axisymmetric problem of transient electric.
Nominal voltage U0 = 35 kV. Surge waveform is defined by IEC 61000-4-5*.
Relative permittivity of the ceramic insulator ε = 3.
Relative permittivity of ZnO element ε = 60, conductivity of ZnO element is a nonlinear function of electric field stress:
Calculate the varistor current.
We specify the voltage as a sum of two components: nominal voltage and the surge pulse. The surge pulse is defined by the double exponential equation*.
35000 + 165000 * (exp(-t/68.2e-6) - exp(-t/0.4e-6))
At nominal voltage the conductivity current is negligible. At overvoltage the resistance value diminishes and conductivity current increases.
|35 kV||0.74 mA|
|194 kV||407 A|
*Reference: IEC 61000-4-5