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Implement metal-oxide surge arrester

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

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).

**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:`

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.

The `power_surgnetwork``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.

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