SOFTWARE>> - 6 -

N° 41 - January 2003 - CEDRAT - CEDRAT TECHNOLOGIES - MAGSOFT Corp.

PSCAD and transmission lines.Fabrice Foucher - CEDRAT, Paul Wilson - MANITOBA HVDC.

Once the transmission line

geometry (or impedances) are

entered, and the solution model

is chosen, PSCAD calls a routine

to compute parameters before

running the simulation. This

routine determines the impedance

and admittance matrix giving the

Vout/Vin transfer function, including

the surge impedance. User can read

the computed values in a subsheet

of the line model.

Example 1We will see several characteristics

of the lines with the following basic

example (fi gure 3).

• Refl ections:

On a transmission line, the

travelling wave times are not

neglected and the wave refl ection

phenomena that can lead to

voltage sags or overvoltages on

the receiving end. The case above

shows clearly the travel time when

comparing both input and output

of the two transmission line phases

to phase voltages. Tline2 is twice

as long as Tline1 with the same

confi guration and separate ROWs.

Thus, a travelling wave takes twice

as long to reach

the end of the

transmission

line Tline2.

See the fi gure 4

below.

PSCAD: The profes-sional power system simulator.

The PSCAD/EMTDC software,

developed by the Manitoba HVDC

Research Centre, recently joined

the family of products distributed

by CEDRAT.

This software is specifically

dedicated to transient simulations

of power systems. The user-friendly

graphical user interface (GUI), the

numerous control tools, its fast

execution speed and interactivity

make PSCAD a convenient tool

for the analysis and design of your

power system.

The study of electrical power

networks is the major focus of the

PSCAD application. The software

includes accurate transmission

line models which allow to take

into account the characteristic

phenomena occurring in the

transmission lines. These

phenomena include line losses, time

travel, refl ections, inductive and

capacitive mutual coupling between

conductors, skin effect, etc.

(continued on

page 7)

The user also en-

ters the param-

eters of the con-

ductors (resistivity,

radius, and bundle

information) and

the geometrical

layout of conduc-

tors on the tower

(distances be-

tween conductors,

sag). It is possible

to defi ne precisely

any tower and

«Right-of-Way»

(ROW) geometry.

Finally, three types

of models are available according to

the application need:

- The PI section model: a lumped

parameter model derived by series

RL elements and parallel CG

elements. This model is adapted

for short lines to study the 50/60Hz

load fl ow, and transient behaviour.

This model is also used when tower

geometry is unknown.

- The bergeron model: models

transmission lines with distributed

parameters and travelling wave

delays. The line is represented with

impedance and admittance matrix

composed of line elements. It is a

convenient model when accurate

harmonics are not too important.

This model is more precise than the

PI section model, particularly when

the transmission line travelling wave

time is longer than the simulation

time-step, i.e. greater than 15km

for 50microseconds.

- Frequency dependend model:

The distributed parameters,

travelling wave model is very

precise over a larger frequency

domain (DC to roughly 50kHz).

All of the frequency dependent

parameters of the cable, conductor,

and ROW are computed.

Figure 1: Line model.

Figure 3: Capacitor switching case.

The transmission lines models

Similar to all components in the

PSCAD Master Library, the PSCAD

interface allows users to quickly

identify and use any T-line model.

The T-line model is linked with the

rest of the power system by means

of the following icons (fi gure1).

We notice that the soon to be

released version 4 of PSCAD allows

users to draw networks in a familiar

single line diagram format.

To apply a transmission line, the user

defi nes the global characteristics of

the transmission line (For example:

number of conductors, fundamental

frequency, and length), and then

the other parameters are defi ned in

a subpage as follow (fi gure2).

Figure 2: Transmission line definition.

SOFTWARE>>

N° 41 - January 2003 - CEDRAT - CEDRAT TECHNOLOGIES - MAGSOFT Corp.

- 7 -

PSCAD and transmission lines. (continued from page 6)Fabrice Foucher - CEDRAT, Paul Wilson - MANITOBA HVDC.

Example 2 : NetworkPSCAD simulates an entire electrical

network, from the source to the

load. With the following example,

we represent a transmission line

from the source to a first node

where the network is separated

into two branches, one simulated

by a three phase RC single line

load, and the other is simulated

with a second transmission line

at a different voltage level. From

there the network is again split into

two branches, both connected by a

short distribution line and a three

phases balanced load.

We can notice that the two

distribution lines in Figure 6 are

simulated by PI section models,

whereas the transmission lines

(figure 5) use more accurate

frequency dependent models.

The breakers are fully represented;

their red or green color allows us

to visualize their operating state

directly during the simulation.

Meters are placed at several

places on the network that will

give instantaneous voltage and

power levels according to the

breaker operations and the load

variations. You can modify the

values of the load with slider

controls during the simulation and

see the effects on the measured

values. The following plots (fi gures

7 and 8) represent the sharing out

of the active and reactive power.

All values have been converted to

per unit quantities, actual units and

even the instantaneous values are

also available. The P0 and Q0 values

correspond to the source and P10

and Q10 values correspond to the

RC load, identifi able by the sign of

the reactive power. Secondly, we

simulate various faults on any of

the branches of the network.

In this example, an A phase to

ground fault at time t=0.9s for

a duration of 0.2s is initiated. All

breakers are closed for the entire

simulation.

(continued on page 11)

Figure 4 : Travelling wavess relections.

Figure 5: Transmission line circuit - Part1.

Figure 6: Distribution circuit – part 2 connected at T-Line2.

Figure 7: Power (pu) plots versus time.

Figure 8: RMS response to an A phase to ground fault.

This fault is controlled by the

component “ Timed Fault Logic ”.

You can notice the parasite

oscillations upstream the fault

(fi gure 8).

It is possible to simulate a fault at

any place in the circuit. A phase-

to-phase fault was recorded and

SOFTWARE>> - 11 -

N° 41 - January 2003 - CEDRAT - CEDRAT TECHNOLOGIES - MAGSOFT Corp.

Switched reluctance motor (SRM) drive modelling

using Flux to Simulink technology. (continued from page 10)

Frederik D’hulster – Hogeschool West-Vlaanderen dept. PIH, Kortrijk, Belgium.

Figure 5 : Simulation results of Flux to Simulink technology.

The output parameters of the FE-analysis are the phase currents, the coil voltages and the instantaneous electromagnetic torque in the airgap. At every time-step (t

s = 2.10-5 s),

data is exchanged between the drive model and the FE-analysis. This method has the great advantage that a complex drive model in Matlab/Simulink® can be used in combination with accurate flux-linkage calculation, taking into account the mutual coupling between adjacent phases. The disadvantage of this method is the rather high calculation time, caused by the high amount of elements in the thin airgap. Figure 5 shows the simulation results of coil voltage, phase current and electromagnetic torque production for a reference current of 7.5 A and a rotor speed of 50 rad/s. The results clearly show that, besides the normal ON, OFF and chopping voltage of phase A, an extra induced voltage

occurs, due to the excitation of adjacent phases D and B. Conform the fl ux distribution of fi gure 3, this voltage is induced in phase A when phase B or D is activated together with

phase C (see fi gure 5).

6 - ConclusionThe Flux to Simulink technology has proven to be an effi cient tool to model complex motor drives in combination with accurate flux-linkage calculation. Effects, such as mutual couplings and induced voltages, can be analysed. Attention must be paid to the sample-time in Matlab/Simulink® and the number of elements in the FE-model in order to keep the computation time acceptable…

Figure 4 : SRM drive model with Flux to Simulink technology.

placed on the line at 30% of its

length from the load (fi gure 9).

As you can see below, breaker

currents from BRK22 were captured

in fi gure 10.

With the accurate models in

PSCAD, you can perform detailed

transient simulations of electrical

networks. The different types

of PSCAD models allow the user

a large degree of freedom in

designing simulations. Whatever

the goal of the study, users can

easily and quickly realize any kind

of simulation, and have discretion

on the degree of accuracy.

Figure 10: Instantaneous traces for a Line to Line fault on A and B phase, 30% of the line.

Figure 9: Fault on the

line.

PSCAD and transmission lines. (continued from page 7)

Fabrice Foucher - CEDRAT, Paul Wilson - MANITOBA HVDC.