# Surge Arrester

Implement metal-oxide surge arrester

## Library

Fundamental Blocks/Elements

## Description

The Surge Arrester block implements a highly nonlinear resistor used to protect power equipment against overvoltages. For applications requiring high power dissipation, several columns of metal-oxide discs are connected in parallel inside the same porcelain housing. The nonlinear V-I characteristic of each column of the surge arrester is modeled by a combination of three exponential functions of the form

`$\frac{V}{{V}_{\text{ref}}}={k}_{i}{\left(\frac{I}{{I}_{\text{ref}}}\right)}^{1/{\alpha }_{i}}.$`

The protection voltage obtained with a single column is specified at a reference current (usually 500 A or 1 kA). Default parameters k and α given in the dialog box fit the average V-I characteristic provided by the main metal-oxide arrester manufacturers and they do not change with the protection voltage. The required protection voltage is obtained by adding discs of zinc oxide in series in each column.

This V-I characteristic is graphically represented as follows (on a linear scale and on a logarithmic scale).

## Dialog Box and Parameters

Protection voltage Vref

The protection voltage of the Surge Arrester block, in volts (V).

Number of columns

The number of metal-oxide disc columns. The minimum is one.

Reference current per column Iref

The reference current of one column used to specify the protection voltage, in amperes (A).

Segment 1 characteristics

The k and α parameters of segment 1.

Segment 2 characteristics

The k and α parameters of segment 2.

Segment 3 characteristics

The k and α characteristics of segment 3.

Measurements

Select `Branch voltage` to measure the voltage across the Surge Arrester block terminals.

Select `Branch current` to measure the current flowing through the Surge Arrester block.

Select `Branch voltage and current` to measure the surge arrester voltage and current.

Place a Multimeter block in your model to display the selected measurements during the simulation. In the Available Measurements list box of the Multimeter block, the measurement is identified by a label followed by the block name.

Measurement

Label

Branch voltage

`Ub:`

Branch current

`Ib:`

## Limitations

The Surge Arrester block is modeled as a current source driven by the voltage appearing across its terminals. Therefore, it cannot be connected in series with an inductor or another current source. As the Surge Arrester block is highly nonlinear, a stiff integrator algorithm must be used to simulate the circuit. `de23t` with default parameters usually gives the best simulation speed. For continuous simulation, in order to avoid an algebraic loop, the voltage applied to the nonlinear resistance is filtered by a first-order filter with a time constant of 0.01 microseconds. This very fast time constant does not significantly affect the result accuracy.

When you use the Surge Arrester block in a discrete system, you will get an algebraic loop. This algebraic loop, which is required in most cases to get an accurate solution, tends to slow down the simulation. However, to speed up the simulation, in some circumstances, you can disable the algebraic loop by selecting Show additional parameters and then Break algebraic loop in discrete model. You should be aware that disabling the algebraic loop introduces a one-simulation-step time delay in the model. This can cause numerical oscillations if the sample time is too large.

## Example

The `power_surgnetwork` example illustrates the use of metal-oxide varistors (MOV) on a 735 kV series-compensated network. Only one phase of the network is represented. The capacitor connected in series with the line is protected by a 30 column arrester. At t = 0.03 seconds, a fault is applied at the load terminals. The current increases in the series capacitor and produces an overvoltage that is limited by the Surge Arrester block. Then the fault is cleared at t = 0.1 seconds.

At fault application, the resulting overvoltage makes the MOV conduct.