modelling an industrial power network bypscad

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APPLICATION NOTES

Figure 1 Single line view of the

PSCAD™ model of an industrial

power network.

The network shown illustrates a model of an industrial power

network used to analyse certain power quality issues. Some of

the issues addressed are:

• Voltage amplification problems due to capacitor bank switching

• Performance of an industrial drive

• Modelling of motor start up

• Modelling of motor loads and normal industrial loads

• Transformer saturation issues

• Harmonics and flicker

• Methods to reduce transients.

The single line view of the PSCAD™ model of this network is shown in

Figure 1. The main distribution network is modelled as an impedance

behind a voltage source. For the study concerned, a simple represen-

tation as shown in Figure 3 was identified as sufficient. If the study

required a more accurate representation of the network frequency

response, more buses behind the 11 kV system bus must be added to

the model.

The source impedance can be determined from the short circuit level

at this bus.

The user may select a more detailed representation for the system

equivalent where a combination of L-R-C elements can be used to

represent the impedance. The zero sequence can be defined to be

different from the positive sequence impedance. The data can be

entered as R, L and C values or in the more common impedance/

phase angle format.

PSCAD™ simulations can be used to design

the optimum value of the insertion resistor.

Figure 4 shows the arrangement of the utility side capacitors. If

there is more than a single bank, more parallel units are

to be added to the model. The short line connecting the capacitors

to the system bus at the substation is represented using series R-L

elements. The user may decide to represent this as a coupled PIsection where the mutual effects between the phases are included.

The utility side capacitors used for voltage support of the bus

also include a 400 Ohm damping resistor. PSCAD™ simulations can

be used to design the optimum value of the resistor. The capacitor

breaker is controlled by Timed Breaker Logic unit but the user may

design the breaker on/off signals using many different arrangements.

Figure 5 Single and double circuit pi

section models.

POWER QUALITY STUDIES

Modelling an

Industrial Power Network

Figure 3 11 kV System Bus.

Figure 4 Utility Capacitor Bank.

Figure 2 Voltage Source Parameters.



The transformer at the customer location is modelled as a

Delta-wye unit made up of single phase banks. PSCAD™ includes

models for three-limbed cores as well as five-limbed cores.

The appropriate model should be selected depending on the actual

arrangement of the unit under study. The following standard data are

required to model the transformer:

• MVA rating and the winding voltage ratings• Impedance

• Percentage no load current

• Losses.

The transformer model takes into account the non-linear

behaviour of the core. Additional data pertaining to the

non-linear no-load characteristics needs to be entered if

saturation is to be included in the solution. Some studies

that would require the inclusion of saturation effects include:

• Harmonic distortion issues at the bus

• Inrush current and protection issues

• Ferro-resonance investigation.

High frequency transients, a serious power

quality issue, can lead to production line

shutdown and unplanned down time.

Figure 6 shows the model of the industrial load. The power factor

correcting capacitors and the motor drive units are modelled along

with the rest of the loads. The loads can be represented as R-L-C

combinations, constant P-Q load, constant current load or any other

method. The power factor correcting capacitor breaker is manually

controlled to easily simulate the switching of the utility capacitors

when this power factor correcting unit is in service and out of service.The main capacitor bank was turned on at 0.5 s in the

simulation results shown in Figure 7. When the PF correcting unit is

on, there is energy exchange between the two capacitors and the

result is an amplified voltage at the customer low

voltage bus. Inclusion of properly sized damping resistors

in parallel with the main capacitors will help reduce the

transient peaks.

The high frequency voltage transients can charge the DC link

capacitor of the machine drive converter. The power electronic

devices are quite susceptible to excessive voltage and the protection is

designed so that the drive will be disconnected in the event of exces-

sive DC link voltage. This is a serious power quality issue as production

lines associated with the drive will undergo unplanned down time.

The capacitor energizing transient can be suppressed using different

strategies.

Synchronized Switching of Breaker Poles

The individual poles of the breaker are closed at corresponding voltage

zero points. A separate control unit is required to issue the synchro-

nized breaker signals (Figure 8).

Figure 6 Industrial Loads

Figure 7 PF unit off, PF unit on and

PF unit on and with no

damping resistor on main caps.

Figure 8 Synchronized Switch-

ing Control.



The Multiple Run component of PSCAD™

can be used to run a number of simulations,

with selected parameters changed

in a controlled manner for each run.

Pre-Insertion Resistance

The breaker model in PSCAD™ allows the user to select

the pre-insertion option and the option to close individual poles

separately.

The detailed model of the Induction motor drive(arranged in a PSCAD™ page module) is shown in Figure 9.

The overvoltage at the DC link capacitor bank can be limited

by the proper design of the capacitor size and the use of

a series inductor in the DC link to limit the rate of charging

of the capacitor.

The Multiple Run component of PSCAD™ can be used to

run a number of simulations, with selected parameters changed in a

controlled manner for each run. The application note on the use of

multiple run component lays out the steps involved in detail.

In the drive example shown in Figure 9, the system side converter

is modelled as an uncontrolled diode bridge. The machine side is a

controlled bridge using IGBT units. The firing pulses are generated

using the control model shown in Figure 11. The control systemblocks required to drive the firing pulses are found in the CSMF

part of the master library. Some useful blocks in designing a more

complex firing control system are shown in Figure 12. These include

the PLL, VCO, Interpolated firing pusle module, comparators and

signal generators.

The control blocks can be used to model the load torque profile.

This is an input to the machine model (Figure 14).

The drive converters produce harmonics. It is necessary to analyse

harmonics produced by the non-linear loads and determine if filter-

ing is required. Figure 13 shows the FFT module that can be used.

Polymeters can be used to display the harmonic profile. This model

can be extended to study the following without much modification

and effort:

• Motor starting transients

• MOV duty during switching events

• Breaker Transient Recovery Voltage issues.

Prepared by Dr. Dharshana Muthumuni. Please email

[email protected] if you have an article you would like

to submit on the use of PSCAD™.

Figure 9 Machine drive arrangment.

Figure 11 Firing pulses generated using the control model.

Figure 14 Load torque as a function of speed.

Figure 10 Multiple Run component.

Figure 12 Blocks in the CSMF library.

Figure 13 FFT module.



Manitoba HVDC Research Centre Inc.244 Cree CrescentWinnipeg, Manitoba, Canada R3J 3W1 T +1 204 989 1240 F +1 204 453 [email protected]

www.pscad.com

Innovation...

in applied research

and development.

The Manitoba HVDC Research Centre performs

innovative research and development into advanced power

system technologies, power electronics and power system

simulation. We offer specializedengineering services and develop leading-edge

technology products for the power systems

community. Founded in 1981, we are part of the

Manitoba Hydro family, Canada’s fourth largest

electrical power and gas utility.

PSCAD™ – Setting the Standard Through the

introduction of the PSCAD™ simulation software,

now used in over 60 countries, the Centre has helped revolu-

tionize power system simulation.

RTDS™ – World’s First RTDS™, the world’s first

real time digital simulator of power systems wasdeveloped at the Centre.

RTP™ – Making Waves Our RTP™ (Real Time Playback)

power system wave-form generator offers portable,

low cost, high fidelity transient testing capability.

Successful Partnerships Longstanding strategic

technology alliances with organisations such as

ABB and Siemens, and a technology advisory board

with representation from research organizations,

universities and electrical equipment manufacturers have

fostered our success – we continue to seek new technology

initiatives and research partnerships.

Power of Positive Thinkers It is thanks to the

extraordinary efforts of our researchers that the

Centre has become a world leader in power systems

simulation technologies, power systems analysis and related

technologies.

With our large worldwide base of technology users

and research partners, we have our finger on the pulse of the

electric energy industry – around the globe.

modelling an industrial power network bypscad

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