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 | |
|---|---|
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Properties:
| Main features:
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Implementation:
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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:
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)