The non-linear resistor model consists mainly of a compiled curve that describes, instantaneously, the behaviour of V with respect to I. It is known that the voltage curve with respect to the current in a resistor is a line whose slope is equal to the value of the resistance.

To represent a surge arrester, this line bends as the voltage increases. Hence, a surge arrester dissipates a greater quantity of current if an over voltage or surge occurs, since its resistance decreases.

The resistor can be characterized as follows:

Non-Linear Resistors Characterization.png

The relation of V must be translated with respect to I (voltage versus current). The user has two options to translate this characteristic. Either the EMTP method, that describes sections in the form of exponential expressions, or using a matrix.

In the first case, the user must provide the information for a number of sections.

For example, the curve drawn in the figure above expresses the I-V relationship in four distinct sections. Three exponential sections (omit section 1 which is linear.) Section 2, delimited by Vmin(0) to Vmin(1) is described with the parameters P(0) and Q(0).

The exponential number i selected will force the user to provide the values of Vmin, P and Q for coefficient 0 to coefficient i-1.

A more simple method consists in describing the curve in a compiled way. For each value of V, the associated current value is entered.

Mask and Parameters

General Parameters

Non-linear Resistor Mask (General Tab)

Name	Description		Unit
Input Data Format	Select the parameter input type, either using the EMTP method (exponential section) or with a matrix.
	EMTP format
	Number of exponentials	Number of exponential sections of the curve (does not include the first linear section).
	Vref	Base voltage on which the value of Vmin is evaluated (V).	V
	Vmin	Value of the voltage for each section change. There are as many Vmin values to provide as there are exponential sections (pu).	p.u.
	P	Value characterizing the exponential section. There are as many P values to provide as there are exponential sections (A).	A
	Q	Value characterizing the exponential section. There are as many Q values to provide as there are exponential sections.	A

Table Parameters

Table Parameters Tab

Name	Description		Unit
Input Data Format	Select the parameter input type, either using the EMTP method (exponential section) or with a matrix.
	Matrix Format
	Symmetry	The user defines the curve from 0 to +Vmax, and this curve is duplicated for the negative section.
	Asymmetry	The user defines a curve from -Vmax to +Vmax. The negative part can differ from the positive part.
	Number of points on the curve	Specifies the number of points characterizing the voltage curve with respect to the current.	p.u.
	V	Vector of voltage points based on the number of points specified by the user. Each point corresponds to a location on the curve.	V
	I	Vector of current points based on the number of points specified by the user. Each point corresponds to a location on the curve.	A

Ports, Inputs, Outputs and Signals Available for Monitoring

Available Signals

At acquisition, the following signals are made available by the sensors:

Name	Description
I(a,b,c)_label	Current per phase in the non-linear resistor.
SEG(a,b,c)_label	Exponential section being used.

Description

Mask and Parameters

General Parameters

Table Parameters

Ports, Inputs, Outputs and Signals Available for Monitoring

Available Signals

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