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.

Problem Type
Axisymmetric problem of transient electric.

Geometry

Given
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:

Task
Calculate the varistor current.

Solution
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))

Results
At nominal voltage the conductivity current is negligible. At overvoltage the resistance value diminishes and conductivity current increases.

*Reference: IEC 61000-4-5

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