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Constant Param, 3-ph


The constant parameter (CP) line model assumes that the line parameters R , L, and C are independent of the frequency effects caused by the skin effect on phase conductors and on the ground. The model considers L and C to be distributed (ideal line) and R to be lumped at three places (line ends R/4 and line middle R/2). The shunt conductance G is taken as zero. The frequency dependence of the line parameters (represented in the FD model) is an important factor for the accurate simulation of waveform and peak values. However, the CP model is very robust, simple, and fast. It also provides a good alternative for a first approximation analysis.

A transposed or untransposed CP line is represented by a) its sequences, or b) its propagation modes and the transformation matrix (Ti) between mode currents and phase currents.

Implementation details can be found in:

H. W. Dommel, "Digital computer solution of electromagnetic transients in single and multiphase networks," IEEE Trans. Power App. Syst., vol. pas-88, pp. 388-99, 04/ 1969.

Table of Contents

Mask and Parameters

General Parameters




Variable = {Possible Values}




Variable = {Possible Values}


Use this field to add information about the component

Description = {'string'}

EMTP (.pun) file for line parameters calculation

The location (path) of the EMTP file (pun file) containing the line parameters

File = {''}

L-C units in EMTP (.pun) file

The units from the pun file can be taken using two options  

L-C units = { 0, 1}

mH/km, uF/km {0}

Inductance (L), capacitance (C) 

Ohm/km, uS/km {1}

Inductive (Xl) and capacitive (Xc) reactances 

Line Length

The length of the line


length = {0, 1e64}


Per unit length resistance for each phase (mode)


R = {'-1e64, 1e64'}


Per unit length inductance for each phase (mode)


L = {'-1e64, 1e64'}


Per unit length capacitor for each phase (mode)


C = {'-1e64, 1e64'}

Base power (perPhase)

Base value for PU conversion

MVA per phase

pBase = { [1, 1e64] }

Base voltage (rmsLN)

Base value for PU conversion

kV rms LN

vBase = { [1, 1e64] }

Base frequency

Base value for PU conversion


fBase = { [1, 1e64] }

Continuously transposed line

Transposition (Untransposed/Transposed)

transp = { 0, 1}

No {0} 

Untransposed line

Yes {1}

Transposed line

Transformation matrix

Transformation matrix between mode current and phase current ([Iphase] = [Ti] x [Imode]); not used in the case of transposed line.

Ti = { [-1e64, 1e64] }

Line Generator

For more information see

Ports, Inputs, Outputs and Signals Available for Monitoring


This component supports a 3-phase transmission line 






Network connection of phases (a,b,c) of the left (+) side


Network connection of phases (a,b,c) of the right side






At acquisition, the signals available by the sensors are:








Bus voltage for each phase (1,2,3)



Current for each phase (1,2,3)


The (1,2) in the previous table indicates the name of the bus at each end of the line (1 for the left (+) side and 2 for the right side)

Electrical Parameters

Calculation of electrical parameters

The Electrical parameters of CP lines can be calculated by using the .

Propagation Delay

The propagation delay is calculated as follows: 

Where i is for each of the phases, L and C stands for the inductance and capacitance of the line per unit length.

When the propagation delay is smaller than the time step in a transposed line, the Constant Param block is automatically replaced by an equivalent PI Line.

For any case, when a CP line is used the simulation time step should be larger than the propagation time of the line. When the propagation delay is smaller than the simulation time a message will appear in the console, here is an example:

If the line is transposed:

WARNING in line: <Name of Block>.
The propagation delay (X) is less than the sample time (Y). A PI line is automatically used.
WARNING in the model [<Name of Block>:]! The line type has changed and the results may be false. Please restart the simulation.

These messages indicate that the line model is automatically changed to a PI model. Since the model is changed, the user needs to restart the simulation (re-analyze and re-generate code). 

If the line is untransposed:

WARNING in line: <Name of Block>.
The propagation delay (X) is less than the sample time (Y). A PI line is automatically used.
ERROR in line: <Name of Block>.
The propagation delay is less than sample time and the line is Untransposed.
A PI line cannot be automatically used. Use a PI line with matrix parameters.

These messages indicate that the model cannot be automatically changed because the line is untransposed. This happens because there are three distinct modes and the PI model only supports two. Thus, if the user wants to simulate a very short untransposed line, the user needs to use a PI line with the matrix parameters.

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