TechRef AC CurrentSource

DIgSILENT PowerFactoryTechnical Reference Documentation

AC Current SourceElmIac

DIgSILENT GmbH

Heinrich-Hertz-Str. 972810 - Gomaringen

Germany

T: +49 7072 9168 00F: +49 7072 9168 88

http://[email protected]

Revision History

Date Author Reviewed by PF Version Doc.Revision17/12/12 M.Martınez F.Fernandez 14.1.6 r512

Copyright ©2011, DIgSILENT GmbH. Copyright of this document belongs to DIgSILENT GmbH.No part of this document may be reproduced, copied, or transmitted in any form, by any meanselectronic or mechanical, without the prior written permission of DIgSILENT GmbH.

AC Current Source (ElmIac) 1

http://www.digsilent.de

mailto:[email protected]

Contents

Contents

1 General Description 3

1.1 Model Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Load Flow Analysis 3

3 Short-Circuit Analysis 4

4 Harmonic Load Flow 5

5 Frequency Sweep 5

6 Dynamic Simulation 7

6.1 RSM Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

6.2 EMT Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

A Parameter Definitions 10

B Signal Definitions 10

List of Figures 11

List of Tables 12


2 Load Flow Analysis

1 General Description

The AC Current Source model represents a constant current injection in the system. It should beconnected to 3 phase AC terminals, as it does not support 2 phase and single phase systems.ElmIac could be used for balanced and unbalanced calculations and could be useful for:

• Wind turbine modeling

• HVDC system modeling

• Photovoltaic modeling

• Injection of harmonic currents in the system

• General circuit analysis

In the Basic Data page of the AC Current Source the main parameter to be entered is the RatedCurrent Ir.

1.1 Model Diagrams

Figures 1.1, 1.2 and 1.3 depict the equivalent positive, zero and negative sequence circuit ofthe model. In contrast with the AC voltage source where it is possible to define negative andzero sequence voltages, in the AC current source the current injection is always in positivesequence. The current injection for both balanced and unbalanced calculations is always inpositive sequence, although the negative and zero sequence internal admittances are consid-ered.

a) Positive Sequence Network

b) Negative Sequence Network

c) Zero Sequence Network




Isetp

I1

G1 B1

G2 B2

I2

G0 B0

I0

Isetp

Isetp

U1

U2

U0

Figure 1.1: Positive sequence AC current source model

2 Load Flow Analysis

The parameters that should be defined for load flow calculations are listed in Table A.1. Outputcurrent is given by the following equation:

I1 =

{(Isetp × Cosφ+ U1 ×G1) + j(IsetpSinφ+ U1 ×B1) if pf Capacitive

(Isetp × Cosφ+ U1 ×G1) − j(IsetpSinφ+ U1 ×B1) if pf Inductive(1)


3 Short-Circuit Analysis







Isetp

I1

G1 B1

G2 B2

I2

G0 B0

I0

U1

U2

U0

Figure 1.2: Zero sequence AC current source model







Isetp

I1

G1 B1

G2 B2

I2

G0 B0

I0

U1

U2

U0

Figure 1.3: Negative sequence AC current source model

I0 = U0 ×G0 + jU0 ×B0 (2)

I2 = U2 ×G2 + jU2 ×B2 (3)

Equations 1 to 3 are used for unbalanced load flow calculations. The balanced option onlyconsiders equation 1.

3 Short-Circuit Analysis

For VDE/IEC and ANSI Short-Circuit calculation there is no defined short-circuit contribution forAC Current Sources.

In the Complete Short-Circuit calculation data of the internal conductance and susceptance forpositive, negative and zero sequence are needed. The ElmIac behaves as a constant cur-rent source for symmetrical faults. For unsymmetrical faults, it behaves as a constant currentsource in the positive sequence network and as a constant admittance in the negative and zerosequence networks.


5 Frequency Sweep

4 Harmonic Load Flow

The AC current source can be used to define harmonic current injections into the network.Figure 4.1 shows how to define the harmonic currents injection. To define the harmonics itis possible to select a spectrum which contains the harmonic currents, for more informationregarding how to define a spectrum refer to User’s Manual ”Definition of Harmonic Injections”.The harmonic current can be referred to either the fundamental or rated current.

Figure 4.1: Harmonic Current Definition

For the Harmonic Current Definition, the selected type can be chosen between Balanced, Un-balanced and according to IEC61000 representation as shown in Figure 4.2.

5 Frequency Sweep

In the frequency sweep calculation the internal current of the current source is set to 0 A and 0deg (open-circuit). The parameter ”Spectral Density of the Current Magnitude/Angle” (didf, dφdfin p.u./Hz, deg/Hz) and the corresponding frequency dependent characteristic allows for thedefinition of an internal current according to equations (4) and (5).


5 Frequency Sweep

Figure 4.2: Harmonic Current Definition Type

ii(ωh) = didf · ichar(ωh) (4)

φIi(ωh) = dφdf · φI,char(ωh) − ∆φIi (5)

where

∆φIi = φIi − φIref (6)

and didf and dφdf are constant input parameters used to scale the frequency characteristicsichar and φI,char in (4). The characteristics can be either polynomial (using the PowerFactoryChaPol object) or a vectorial characteristic (using the ChaVec object) with a frequency scale(using the TriFreq object). The angle ∆φIi accounts for the angle deviation between the currentand the system reference voltage angle.

A common application is the analysis of the transfer function of a part of the system or thepropagation of a current impulse in frequency domain. To do this the amplitude and phase ofthe spectrum current can be defined and using the frequency sweep function, the voltage at theremote end can be calculated.


6 Dynamic Simulation


For the RMS/EMT simulation we can independently control the phases A, B and C. Please notethat this is not the case of the LDF calculations. For RMS and EMT simulations there is theoption for balanced and unbalanced models as shown in Figure 6.1.







Isetp

I1

G1 B1

G2 B2

I2

G0 B0

I0

U1

U2

U0

isetp

isetp

isetp G1 B1

G2 B2

G0 B0

u1

u2

u0i0

i2

i1

(a) Positive sequence







Isetp

I1

G1 B1

G2 B2

I2

G0 B0

I0

U1

U2

U0

isetp

isetp

isetp G1 B1

G2 B2

G0 B0

u1

u2

u0i0

i2

i1

(b) Zero sequencea) Positive Sequence Network






Isetp

I1

G1 B1

G2 B2

I2

G0 B0

I0

U1

U2

U0

isetp

isetp

isetp G1 B1

G2 B2

G0 B0

u1

u2

u0i0

i2

i1

(c) Negative sequence

Figure 6.1: RMS and EMT AC current source model.

6.1 RSM Simulation

For RMS simulation the user has the option to control the current source in two different waysdepending of which signals from defined in Table B.1 are used. When the current (i0, I0) andfrequency (f0, F0Hz) input are connected together with the additional angle magnitude, phaseand frequency of the AC current source are controlled. The resulting output current is definedby equation 7.

i = i0 cos(2πf0t+ phii+ dphii) + j sin(2πf0t+ phii+ dphii) (7)

Also is possible independently control magnitude and phase for A, B and C components usingthe signals: I A, I B, I C, phii B, phii C and dphii. PowerFactory internally applies the ParkTransformation to works with dq0 components. The angle for phase A can be configured withthe input parameter dphii and the internal reference phii, both in rad. phii is calculated internallyby PowerFactory and can change if the network conditions change. The power factor set pointdefines the steady state initial value of dphii. The derivative of phii is being changed if there is afrequency change: f0 is connected, the derivative of phii is set to 2∗PI ∗f ∗(f0−fref); f0 is notconnected, the derivative of phii is set to 2 ∗ PI ∗ F0Hz − 2 ∗ PI ∗ f ∗ fref . fref is automaticallyset and should not be connected.

The current source gives an injection with current phase angle defined as follows:



ϕA = phii+ dphii (8)

Angles of phase B and C are relative to the angle of phase A.

ϕB = ϕA + phii B (9)

ϕC = ϕA + phii C (10)

If the two angle signals phii B and phii C are not connected, the program will use a default120◦ shift to calculate the two angles.

ϕB = ϕA − 120◦ (11)

ϕC = ϕA + 120◦ (12)

6.2 EMT Simulation

In EMT studies positive, negative and zero sequence models shown in Figures 1.1 to 1.3 areconsidered. And as for RMS simulation it is possible to control the source in two different ways.When inputs i0, I0, f0, F0Hz are connected the current injection is the same as defined byequation 7 but there is also a negative sequence current defined by the differential equation 13.

i0(t) = G0u0(t) +B0

2πf

∂

∂tu0(t) (13)

When magnitude and phase signals are connected the model is defined as in RMS simulation.

The use of input and output signals from the dynamic model shown in Figure 6.2 could be usedto control the current injection into a system. This is useful to model a current impulse sourceor to define a lightning current standard model.

With the help of a composite model, the user can use a Fourier source ElmFsrc to inject har-monic currents during an EMT simulation. For more information please refer to Fourier SourceTechnical Reference.



i0

I0

I_A

I_B

I_C

phii_B

F0Hz

f0

dphii

phii_C

fref

xspeedRMS

Simulation

i0

I0

I_A

I_B

I_C

F0Hz

f0

dphii

EMT

Simulation

Figure 6.2: Input/Output Definition of AC Current Source (RMS-Simulation)

i0

I0

I_A

I_B

I_C

phii_B

F0Hz

f0

dphii

phii_C

fref

xspeedRMS

Simulation

i0

I0

I_A

I_B

I_C

F0Hz

f0

dphii

EMT

Simulation

Figure 6.3: Input/Output Definition of AC Current Source (EMT-Simulation)


B Signal Definitions

A Parameter Definitions

Table A.1: Parameters of AC Current Source

Parameter Description Unit

loc name Nameoutserv Out of Servicechr name Characteristic Namefor name Foreign Keybus1 Terminal (StaCubic)bus1 bar TerminalcpZone ZonecpArea AreaIr Rated Current Aisetp Positive Sequence Current Setpoint p.u.cosini Positive Sequence Power Factori cap Positive Sequence Reactive PowerG1 Positive Sequence Internal Conductance SB1 Positive Sequence Internal Susceptance SG2 Negative Sequence Internal Conductance SB2 Negative Sequence Internal Susceptance SG0 Zero Sequence Internal Conductance SB0 Zero Sequence Internal Susceptance Sdcurdf Spectral Density of Current Magnitude p.u./Hzfchardcur Frequency Dependency Adphidf Spectral Density of Current Angle deg/Hzfchardphi Frequency Dependencyphmc Harmonic Current Injectionsicurref Harmonic Current Injections Referred toiAstabint A-stable integration algorithmcTypHmc Harmonic Current Injections: Type of Harmonic SourcesInom Harmonic Current Injections: Rated Current

B Signal Definitions

Table B.1: Input/Output signals

Name Description Unit Type Model

i0 Current-Input p.u. IN RMS, EMTI0 Current-Input kA IN RMS, EMTf0 Frequency-Input p.u. IN RMS, EMTF0Hz Frequency-Input Hz IN RMS, EMTI A Current, Magnitude kA IN RMS, EMTI B Current, Magnitude kA IN RMS, EMTI C Current, Magnitude kA IN RMS, EMTphii B Current, Angle, Phase b deg IN RMSphii C Current, Angle, Phase c deg IN RMSdphii Additional Angle rad IN RMS, EMTfref Reference Frequency p.u. IN RMSxspeed Frequency p.u. OUT RMS


List of Figures

List of Figures

1.1 Positive sequence AC current source model . . . . . . . . . . . . . . . . . . . . . 3

1.2 Zero sequence AC current source model . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 Negative sequence AC current source model . . . . . . . . . . . . . . . . . . . . 4

4.1 Harmonic Current Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.2 Harmonic Current Definition Type . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

6.1 RMS and EMT AC current source model. . . . . . . . . . . . . . . . . . . . . . . 7

6.2 Input/Output Definition of AC Current Source (RMS-Simulation) . . . . . . . . . . 9

6.3 Input/Output Definition of AC Current Source (EMT-Simulation) . . . . . . . . . . 9


List of Tables

List of Tables

A.1 Parameters of AC Current Source . . . . . . . . . . . . . . . . . . . . . . . . . . 10

B.1 Input/Output signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10


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