Industrial Network Example

DIgSILENT PowerFactory ∗

Abstract

This paper describes the modelling of an in-dustrial network, which is part of the Pow-erFactory examples. It has different voltagelevels, and supplies AC and DC loads. Typi-cal calculations for analysing the network areprepared in the example and described inthe following:

• Load flow calculation

• Short-circuit calculation

• Harmonics calculation

• Motor starting simulation

• Over-current protection

• Arc-flash hazard calculation

1 Description of the Indus-trial Network Model

The industrial network example containstwo subsystems, each of them is suppliedby an HV/MV transformer. In case of atransformer outage both systems can belinked on the MV level. In total the sys-tems consists of three synchronous motors,14 medium voltage asynchronous motors,four DC motors, one generation unit (syn-chronous generator), one emergency gen-erator (synchronous generator) and one lowvoltage equivalent motor, which represents10 LV asynchronous motors. Even though

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the equivalent motor represents 10 motorsin total, in the basic grid model a number ofonly seven motors in parallel is considered,since it is unlikely that all ten motors are run-ning at full power at the same time. The vari-ation ”Number of parallel motors” containsthe full ten motors, as it is needed for theshort-circuit calculation.

Due to the huge amount of asynchronousmachines the network has a quite low powerfactor. Therefore equipment for power fac-tor correction is used. On Subsystem A aswitchable capacitor bank is used with re-mote control on ”Terminal HV trf 110/10kVA”. On Subsystem B an SVC (Static VarCompensator / System, SVS) is used withremote control on ”Terminal HV trf 110/10kVB”.

2 Load Flow

The first study case (”01 - Load Flow”) is pre-pared to perform load flow calculations. Thisenables the user to have an overview of theresulting voltages as well as the impact ofautomatic tap changing of the transformersand the automatic shunt adjustment to con-trol the power factor.

3 Harmonics

The rectifiers of the four DC motors are con-nected via Yy0 and Yd5 transformers to formtwo 12-pulse rectifiers. There is another rec-tifier connected to the busbar of the PriorityLoad. The rectifiers are causing harmonicdistortions in the AC grid.

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Industrial Network Example

In the Study Case ”02 - Harmonics” thereare some predefined harmonic distortion di-agrams with the allowed limits shown. Forthe priority busbar user-defined limits are ap-plied, which represent some special needsfor harmonic sensitive loads. By calculat-ing the harmonic load flow, the actual har-monic distortions can be analysed. Withoutfurther measures these distortions would ex-ceed the limits. Therefore local filters areconnected to reduce the harmonic voltagesto acceptable levels.

4 Motor Start

Each motor in the networks has a specifictorque characteristic. The motors ”Asm D-1Sys B”, ”Asm D-2 Sys B”, ”Asm D-3 Sys B”,”Asm D-4 Sys B” and ”Asm D-5 Sys B” aremodeled with different starting methods. Foranalysing the starting of these motors, ei-ther a simplified static simulation or a precisedynamic simulation can be used. The re-sults are reported in the PowerFactory Out-put Window. In case of dynamic simulationsthe results are displayed by means of time-dependent result curves in diagrams. Ac-cording result diagrams are adjusted in theStudy Case ”03 - Motor Start”. It is possibleto analyse the start of only a single motor,or of several motors (a motor group) at thesame time. It is also possible to define start-ing sequences by adjusting different startingtimes for the individual motors in the dynamicsimulation.

5 Protection / AC Short-Circuit

The industrial network provides various over-current relays. Relays of feeders are alsoequipped with an interlock. As described inSection 1 the Study Case ”04 - Protection /AC Short-Circuit” uses the variation ”Numberof parallel motors” with all ten parallel LV mo-tors considered. This enables the completeshort-circuit contribution from all machines.

After calculating the short-circuit current onany busbar of the AC network [1], the trippingtime of the different relays are displayed in

the corresponding result boxes. On the pre-pared Time-Overcurrent diagrams inside thepreviously mentioned Study Case the char-acteristics of relays are visible.

6 DC Short-Circuit

Since PowerFactory Version 15.1 calcula-tions of short-circuit currents within DC gridsup to 250 V are supported [2]. An appropri-ate DC short-circuit calculation is preparedin the Study Case ”05 - DC Short-Circuit”.

7 Arc Flash

The Arc-Flash Hazard Analysis calculation ismeant to determine the arc-flash hazard dis-tance and the incident energy to which em-ployees could be exposed during their workon or near electrical equipment [3]. The re-sults may be used to categorize the busbarsdue to their protection group. It is possibleto create corresponding Arc-Flash WarningLabels automatically.

References

[1] IEC 60909-0:2001 ”Short-circuit cur-rents in three-phase a.c. systems - Part0: Calculation of currents”

[2] IEC 61660-1:1997 ”Short-circuit cur-rents in d.c. auxiliary installations inpower plants and substations”

[3] IEEE 1584-2002 ”Guide for PerformingArc-Flash Hazard Calculations”

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