DigSilent TechRef_StaCt

DIgSILENT PowerFactory Technical Reference Documentation

Current Transformer StaCT

DIgSILENT GmbH Heinrich-Hertz-Str. 9 72810 - Gomaringen Germany T: +49 7072 9168 0 F: +49 7072 9168 88 http://www.digsilent.de [email protected] Version: 2016 Edition: 1

Copyright © 2016, 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 means electronic or mechanical, without the prior written permission of DIgSILENT GmbH. Current Transformer (StaCT)

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Contents

Contents 1 General Description

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2 Integration in the relay scheme

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3 Features & User interface

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3.1 Current Transformer Type (TypCt) . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.1.1 Basic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.1.2 Additional data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.1.3 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.2 Current Transformer (StaCt) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.2.1 Basic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.2.2 Additional Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.2.3 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4 Transfer functions 4.1

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Load Flow, Short-circuit and RMS simulation Model . . . . . . . . . . . . . . . .

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4.1.1 CT with Y connection on secondary side . . . . . . . . . . . . . . . . . . .

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4.1.2 CT with D connection on the secondary side . . . . . . . . . . . . . . . .

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4.2 EMT simulation Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4.2.1 CT with Y connection on secondary side . . . . . . . . . . . . . . . . . . .

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4.2.2 CT with D connection on secondary side . . . . . . . . . . . . . . . . . .

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5 Ct saturation models

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5.0.3 Piecewise Linear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5.0.4 Polynomial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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A Parameter Definitions

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A.1 Current Transformer Type (TypCt) . . . . . . . . . . . . . . . . . . . . . . . . . . .

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A.2 Current Transformer (StaCt ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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B Signal Definitions B.1 Single phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Current Transformer (StaCT)

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Contents

B.2 3 phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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List of Figures

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List of Tables

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Current Transformer (StaCT)

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2

1

Integration in the relay scheme

General Description

The Ct block simulates the behavior of a current transformer. Internally two models are available: a “basic” model and a “detailed” model. The “basic” model simulates only the current conversion operated by the CT ratio and by the CT windings connection. The “detailed” model simulates the core saturation effect accordingly with the parameters defined by the IEC and the ANSI standards. Two different types of CT block are available: the 3 phase CT and the single phase CT. Each type has different input and output signals.

2

Integration in the relay scheme

The CT type class name is TypCt; the CT class name is StaCt. The block represents in the relay model scheme the current signals entry point. Usually the CT block is connected to the measurement block. In figure 2.1 the typical connection scheme of a 3phase Ct block is shown, in figure 2.2 the same scheme for a single phase Ct . The Ct is connected to the Measurement block inputs.

Figure 2.1: DIgSILENT The Current Transformer “StaCt” 3 phase connection scheme with the measurement element.

Figure 2.2: DIgSILENT The Current Transformer “StaCt” single phase connection scheme with the measurement element.

Current Transformer (StaCT)

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3

Features & User interface

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Features & User interface Current Transformer Type (TypCt) Basic data

The “Basic Data” tab page allows to define the available transformer ratios in terms of number of windings at the primary and the secondary side.

3.1.2

Additional data

In the “Additional data” tab page the CT accuracy can be defined using the IEC-Apparent Power and the ANSI Burden and Voltage standard. When the selected standard is “Ansi ©-Burden”, the CT burden (“Zb” variable) is entered directly. When the selected standard is not “Ansi ©-Burden”, the CT burden (“Zb” variable) is calculated using the following formulas: Ansi ©Voltage: Zb = Vmax /(aclimit ∗ In ) IEC Apparent Power: Zb = Snom /(In ∗ In ) where Vmax = Voltage Limit (“Vm” variable) aclimit = Accuracy Limit Factor (“aclimit” variable in the Current Transformer Type dialog (“TypCt” class)) In = Secondary side CT rated current Snom = Apparent Power(“Snom” variable)

3.1.3

Description

The Description tab page can be used to insert some information to identify the StaCt type element (both with a generic string and with an unique textual string similar to the Foreign Key approach used in the relational databases) and to identify the source of the data used to create it. Other text fields allow to insert the manufacturer name and a longer description.

3.2

Current Transformer (StaCt)

The user can change the block settings using the “Current Transformer”dialog (“StaCt” class). The dialog consists of three tab pages: Basic data, Tripping times, Additional Data, and Description. The main settings are located in the Basic data tab page.

3.2.1

Basic data

The “Basic Data” tab page of the CT dialog (“StaCt” class) should be used to set the CT type(Type control), transformer ratio (Primary and Secondary Tap comboboxes), measurement

Current Transformer (StaCT)

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3

Features & User interface

point (Location control), orientation (Orientation combobox), secondary side connection (Connection combobox), number of phases (No.Phases combobox, “iphase” variable) and phase order (Phase 1 and Phase 2 comboboxes). The block can be disabled using the Out of service check box. The blue text provides additional info regarding the current ratio. Please note that the Location control can point to another Current Transformer. In this way the other CT output signals can be used as input signals of the CT block. The Location control can point also to a cubicle(“StaCubic” class), to a switch(“StaSwitch” class) or to a 3 Windings transformer (“ElmTr3” class). When the Location control is not used the Measure at is displayed just below the Branch control and it allows setting the measurement point at the switch position or at CT block itself.

3.2.2

Additional Data

The internal model is by default the basic model. To take care of the saturation effects the detailed model can be activated using the Detailed Model check box in the “Additional data” tab page of the CT block dialog (“StaCt” class).

3.2.3

Description

The Description tab page can be used to insert some information to identify the Current Transformer element (both with a generic string and with an unique textual string similar to the Foreign Key approach used in the relational databases) and to identify the source of the data used to create it.

Current Transformer (StaCT)

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4

Transfer functions

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Transfer functions

When the “Detailed model” is not enabled the following transfer formulas are applied: When the primary connection is Y and the secondary connection is Y. Ixsecondary = Ixprimary /ratio where ratio = the CT transformer ratio x = phase a,b,c When the primary connection is Y and the secondary connection is D Ixysecondary = (Ixprimary − Iyprimary )/ratio where ratio = the CT transformer ratio x = phase b,c,a y = phase a,b,c Please consider that when the CT is located in a bus bar cubicle or when the Location control is pointing to a cubicle or to a switch the rated voltage of the bus bar at which the cubicle (or the switch) belongs is used to calculate the following formula: √ Ixprimary = 1000/( 3 ∗ Un ) When the Location control is pointing to another CT or to a 3 windings transformer the following formula is used: Ixprimary = I ∗ unit where unit = 1 for the other Ct case and unit = 1000 for the 3 windings transformer case (to take care of the transformer rated power unit)

4.1

Load Flow, Short-circuit and RMS simulation Model

Figure 4.1: DIgSILENT The Current Transformer “StaCt” LDF, Short Circuit, RMS model. Current Transformer (StaCT)

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4

Transfer functions

The saturation of the magnetizing admittance is not considered for this model The magnetizing admittance is calculated using the following equations: PF Version< 14.0.522 YM = −j ∗ curmg/Zb PF Version> 14.0.522 YM = −j ∗ curmg/Zbnom where curmg is the Excitation Current /Rated Current (in the CT element, “StaCt” class). Zbnom is the nominal burden impedance. The burden impedance Zb is calculated by using the CT element parameter Zburd and cosburd with the following formula: √ Zb = Rb + jXb = Zburd cos(cosburd) + jZburd 1 − cosburd2

4.1.1

CT with Y connection on secondary side

The secondary current is calculated with the following formula: I2x = I20x

1 1 + YM (Rs + Zb )

and I20x =

I1x ratio

where I1x = primary current with x = phase A,B,C ratio =CT transformer winding ratio = ptapset/stapset (primary tap / secondary tap)

4.1.2

CT with D connection on the secondary side

The secondary current is calculated using the following equations: I2x = Ibx − Iby where x is phase A,B,C and y is phase B,C,A and

Current Transformer (StaCT)

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4

Transfer functions

Ibx = (I20x − I20 )

1 1 + YM (Rs + 3Zb )

where x is phase A,B,C I20 = (I20A + I20B + I20C )/3 (zero sequence current)

I20x =

I1x ratio

where x is phase A,B,C and y is phase B,C,A ratio =CT transformer winding ratio = ptapset/stapset (primary tap / secondary tap) The excitation voltage is calculated: Vex = Ibx (Rs + 3Zb )Rs ID0 where x is phase A,B,C with

ID0 = I20

4.2

1 1 + YM Rs

EMT simulation Model

Figure 4.2: DIgSILENT The Current Transformer “StaCt” EMT simulation model.

The Magnetizing Inductance (1/Lm) is calculated accordingly with the following formula:

Bm =

Current Transformer (StaCT)

curmg ωN Zbnom

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4

Transfer functions

where curmg is the Excitation Current /Rated Current (in the CT element, “StaCt” class). Zbnom is the nominal burden impedance. ωN = 2πFnom with Fnom = Nominal Frequency. The Saturated Magnetizing inductance (1/Lmsat) is calculated accordingly with the following formula: Bmsat =

bmsat ωN Zbnom

where bmsat is the Saturated Admittance in p.u. (based on the nominal burden impedance). ωN = 2πFnom with Fnom = Nominal Frequency. Zbnom is the nominal burden impedance calculated as follow: √ Lb = Zburd ∗

1 − cosburd2 ωN

The derivative of the magnetic flux is calculated with the following formula: dpsimx = ωN Vex dt where x is phase A,B,C. Vex is the excitation voltage for the phase x. ωN = 2πFnom with Fnom = Nominal Frequency.

4.2.1

CT with Y connection on secondary side

The excitation voltage is calculated with the following formula:

Vex = (Rs + Rb )I20x + Lb

I20x =

dI20x dt

√ I1x 2 − Iex ratio

where I1x is the primary current with x = phase A,B,C ratio =CT transformer winding ratio = “ptapset”/“stapset” (primary tap / secondary tap). Iex is the Excitation Current with x = phase A,B,C.

4.2.2

CT with D connection on secondary side

The excitation voltage is calculated with the following formula: Current Transformer (StaCT)

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5

Ct saturation models

Vex = Rs (I20x + ID0 ) + 3Rb I20x + 3Lb

dI20x dt

with Iex = Excitation Current with x = phase A,B,C √ I1A + I1B + I1C ID0 = 1/3( 2 − IeA − IeB − IeC ) ratio where I1A is the phase A primary current. I1B is the phase B primary current. I1C is the phase C primary current. ratio =CT transformer winding ratio = “ptapset”/“stapset” (primary tap / secondary tap). IeA = Phase A Excitation Current. IeB = Phase B Excitation Current. IeC = Phase C Excitation Current. The secondary current is: I20x =

√ I1x 2 − Iex − ID0 ratio

where I1x is the primary current with x = phase A,B,C. ratio =CT transformer winding ratio = “ptapset”/“stapset” (primary tap / secondary tap). Iex = Excitation Current with x = phase A,B,C.

5 5.0.3

Ct saturation models Piecewise Linear

In the non-saturated condition the excitation current is calculated by the following equation:

Iex =

Bm psimx ωN

In the saturated condition (psimX > psimknee)by the following equation:

Iex =

with psimknee =

√

Bm Bmasat psimknee + (psimx − psimknee ) ωN ωN

2Vs

where Vs = is the Saturation Voltage (“Vs” variable in the “Excitation Parameter” frame in the Current Transformer dialog (“StaCt” class)).

Current Transformer (StaCT)

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5

Ct saturation models

5.0.4

Polynomial

The excitation current is calculated with the following formula: Iex = f (Bmsat ,Bm ,psimx ,ksat,Vs ) When I < Iknee

Iex =

BM Ixprim ksat Ixprim (1 + |( ) |) ω P0

When I > Iknee BM (Ixprim − Pknee ) ω

Iex = Iknee +

with  BM sat − 1   BM  − ln   Ksat + 1  

Ksat

P0 = Pknee ∗ e and

Pknee =

√

 2

Ksat + 1 ksat



where ksat is the Exponent (“Ksat” variable in the “Excitation Parameter” frame in the Current Transformer dialog (“StaCt” class)). Vs = is the Saturation Voltage (“Vs” variable in the “Excitation Parameter” frame in the Current Transformer dialog (“StaCt” class)).

Current Transformer (StaCT)

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A

Parameter Definitions

A

Parameter Definitions

A.1

Current Transformer Type (TypCt) Table A.1: Input parameters of Ct type (TypCt)

Parameter loc name Primtaps Sectaps iopt sat

Snom Zb Vmax raclass aclimit Ithr

A.2

Description Name assigned by the user to the block type The list of the available number of windings at the primary side (i.e. 50,100,200,500 etc) List of the available number of windings at the secondary side (i.e. 1, 5) The kind of CT representation. It can be “IEC- Apparent Power” internal string:“iec”, “ANSI©-Burden” internal string:“anscb”or “ANSI©-Voltage” internal string:“anscv” Current transformer apparent power (“IEC-Apparent Power” representation) Burden impedance (“ANSI©-Burden” representation) Voltage limit (default values 100, 200,400,500,800) (“ANSI©-Voltage” representation) Accuracy class (default values: 5,10) Accuracy limit factor (default values: 5, 10, 15, 20, 30 ) Rated short circuit current (the max current which can be sustained or 1 sec)

Unit Text Array of real numbers Array of real numbers Text

VA Ohm Volt Integer Integer Primary Amperes

Current Transformer (StaCt ) Table A.2: Input parameters of Ioc element (RelIoc ))

Parameter loc name Typ id Outserv loc name typ id outserv pbranch ilocation iorient ptapset itapset stapcon iphase it2p1 it2p2 Iconsat Zburd cosburd Rs itrmt curmg bmsat Vs ksat

Description Name assigned to the user to the block element Pointer to the relevant TyIoc object Flag to put out of service the block The user assigned name of the Ct type Pointer to the CT type object (TypCt clas) Flag to enable /disable the block Location where the CT is (if it is not set the default location is the cubicle where the CT has been created) Place where the CT is measing the current (it can be “Circuit element” id = 0, “Element” id = 1 CT orientation (it can be “Branch” internal id = 0 or “Busbar” internal id = 1 Primary side number of windings (its one of the value listed in the “primtaps” list in the TypCt object) Secondary side number of windings (its one of the value listed in the “sectaps” list in the TypCt object) Secondary side connection type (it can be “Y” internal id = 0 or “D” internal id = 1) CT number of phases (it can be “1”, “2” or “3”) Phase 1 name (it can be “a”, “b”,“c”,“N”,“I0”) Phase 2 name (it can be “a”, “b”,“c”) Detailed model (considering saturation) activation flag Burden impedance Burden cosφ Secondary winding resistance Saturation model (it can be “Piecewise Linear” internal ID = 0 or “Polynomial” internal ID = 1) Excitation Current/rated Current Saturated Admittance Saturation Voltage Saturation exponent for the polynomial representation . Typical values are 9,13,15.

Current Transformer (StaCT)

Unit Text Pointer Y/N Text Pointer Integer Pointer Integer Integer Real number Real number Integer Integer Integer Integer Integer Real number Ohm Real number Real number Ohm Integer Real number pu Real number Ohm Real number Volt Integer

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B

Signal Definitions

B

Signal Definitions

B.1

Single phase Table B.1: Input/output signals of the single phase StaCt element (CalStaCt1p)

Name Ir A Ir B Ir C Ii A Ii B Ii C I2r I2i I2r A I2i A I0x3r I0x3i

B.2

Description Ct block phase A primary side current real part Ct block phase B primary side current real part Ct block phase C primary side current real part Ct block phase A primary side current imaginary part Ct block phase B primary side current imaginary part Ct block phase C primary side current imaginary part Secondary side current real part Secondary side current imaginary part Secondary side current real part (equal to I2r) Secondary side current imaginary part (equal to I2i) Zero sequence current real part (calculated internally) Zero sequence current imaginary part (calculated internally)

Unit Primary Amps Primary Amps Primary Amps Primary Amps Primary Amps Primary Amps Secondary Amps Secondary Amps Secondary Amps Secondary Amps Secondary Amps Secondary Amps

Type IN IN IN IN IN IN OUT OUT OUT OUT OUT OUT

Model Any Any Any Any Any Any Any Any Any Any Any Any

3 phase Table B.2: Input/output signals of 3 phase Current Transformer element (CalStaCt)

Name Ir A Ir B Ir C Ii A Ii B Ii C I2r A I2r B I2r C I2i A I2i B I2i C I0x3r I0x3i

Description Ct block phase A primary side current real part pu Ct block phase B primary side current real part pu Ct block phase C primary side current real part pu Ct block phase A primary side current imaginary part pu Ct block phase B primary side current imaginary part pu Ct block phase C primary side current imaginary part pu Phase A secondary side current real part Phase B secondary side current real part Phase C secondary side current real part Phase A secondary side current imaginary part Phase B secondary side current imaginary part Phase C secondary side current imaginary part Zero sequence secondary side current real part (calculated internally) Zero sequence secondary side current imaginary part (calculated internally)

Current Transformer (StaCT)

Unit Primary Amperes Primary Amperes Primary Amperes Primary Amperes Primary Amperes Primary Amperes Secondary Amperes Secondary Amperes Secondary Amperes Secondary Amperes Secondary Amperes Secondary Amperes Secondary Amperes

Type IN IN IN IN IN IN OUT OUT OUT OUT OUT OUT OUT

Model Any Any Any Any Any Any Any Any Any Any Any Any Any

Secondary Amperes

OUT

Any

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List of Figures

List of Figures 2.1 DIgSILENT The Current Transformer “StaCt” 3 phase connection scheme with the measurement element. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2.2 DIgSILENT The Current Transformer “StaCt” single phase connection scheme with the measurement element. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

4.1 DIgSILENT The Current Transformer “StaCt” LDF, Short Circuit, RMS model. . .

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4.2 DIgSILENT The Current Transformer “StaCt” EMT simulation model. . . . . . . .

9

Current Transformer (StaCT)

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List of Tables

List of Tables A.1 Input parameters of Ct type (TypCt) . . . . . . . . . . . . . . . . . . . . . . . . .

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A.2 Input parameters of Ioc element (RelIoc )) . . . . . . . . . . . . . . . . . . . . . .

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B.1 Input/output signals of the single phase StaCt element (CalStaCt1p) . . . . . . .

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B.2 Input/output signals of 3 phase Current Transformer element (CalStaCt) . . . . .

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Current Transformer (StaCT)

16