Surge Arrester

EHS SOLVER

This block implements the model of a metal-oxide varistor (MOV) also called a surge arrester, typically used as protection against overvoltages for electrical equipment. The nonlinear nature of the MOV V-I curve is approximated by a piecewise linear function made up of up to 17 V-I points, including the zero point.

The model consists of a controlled current source in parallel with an RC snubber. The value of the generated current is determined by the voltage measured across it, which is then sent to a lookup table that has the V-I data points mentioned above.

 

Parameters (Current-voltage table mode)

Parameter constraints (Current-voltage table mode)

For the current voltage parameters file, such constraints apply :

• A minimum of 3 points and a maximum of 17 points for the current breakpoints and voltage values.

• The same number of points for the current breakpoints and voltage values.

• The voltage values need to be monotonically increasing

Parameters (k and alpha parameters mode)

The calculation of those data points is based on the MOV protection voltage (V_ref), the reference current (I_ref) and the number of columns (metal-oxide discs of the MOV). Then three exponential segments of the curve are calculated with the parameters 

and

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. The default values for the latter two parameters are chosen to fit the average V-I characteristics of MOV manufacturers. Therefore, based on the parameters listed here, 17 data points (including zero) are calculated with the following equations.

• The V-I characteristic of the curve: 

  LaTeX Math Block

• The current values at the transition points between segments 1 to 2 and 2 to 3:

  LaTeX Math Block
  LaTeX Math Block
  LaTeX Math Block

where N_c is the number of columns.

 

Parameter constraints (k and alpha parameters mode)

By design, such 2 constraints apply :

• 𝛼₁ > 𝛼₂ > 𝛼₃

• k₁ < k₂ > k₃