Shunt & Series Non-linear Resistors

Introduction

The non-linear resistor model was developed to represent the different surge arresters found in the network. This model is similar to the one found in EMTP. It allows representing any form of non-linear current-voltage relation, in addition to the typical behaviour of surge arresters. The model has two implementations: parallel or series connection.

Non-Linear Resistors Icons and Diagrams

Series and Parallel Non-Linear Resistors

Properties: 7 Instant description of the voltage behavior with respect to the current	Main features: Dissipate a greater quantity of current if an overvoltage or surge occurs, since its resistance decreases
	Implementation: Series connection

Non-Linear Resistor Model
The non-linear resistor model consists mainly of a compiled curve that describes, instantaneously, the behavior 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 overvoltage or surge occurs, since its resistance decreases.

The resistor can be characterized as follows:

Non-Linear Resistor Characterization

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 Figure 6 - 7 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.

General Parameters

Connection:

For series elements, Series only
For single-phase shunt elements, only a Y ground connection is allowed
For three-phase shunt elements, Y ground, Y floating or Delta are allowed

Parameter Input

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)
Vmin	Value of the voltage for each section change. There are as many Vmin values to provide as there are exponential sections (pu)
P	Value characterizing the exponential section. There are as many P values to provide as there are exponential sections (A)
Q	Value characterizing the exponential section. There are as many Q values to provide as there are exponential sections

Matrix Format

Positive part versus negative part

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.(From 1 to 30)
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)

List of Available Signals
At acquisition, the following signals are made available by the sensors:
• I(a,b,c)_label: Current per phase in the non-linear resistor;
• SEG(a,b,c)_label: Exponential section being used.

Control Panels
The following figures show the control panels of non-linear resistors.

Control Panel of a Non-Linear Shunt Resistor (General)

Control Panel of a Non-Linear Shunt Resistor (Table)