DIgSILENT
PowerFactory 2016
Technical Reference Documentation
Current Transformer
StaCT
I N T E G R AT E D P O W E R S Y S T E M A N A LY S I S S O F T W A R E F O R
TRANSMISSION
/
DISTRIBUTION
/
INDUSTRY
/
G E N E R AT I O N
/
I N T E G R AT I O N O F R E N E W A B L E S
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DIgSILENT GmbH
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72810 Gomaringen / Germany
Tel.: +49 (0) 7072-9168-0
Fax: +49 (0) 7072-9168-88
info@digsilent.de
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http://www.digsilent.de
Copyright © 2016 DIgSILENT GmbH
All rights reserved. No part of this
publication may be reproduced or
distributed in any form without written
permission of DIgSILENT GmbH.
September 2016
Version: 2016
Edition: 2
Contents
Contents
1 General Description
1
2 Integration in the relay scheme
1
3 Features & User interface
2
3.1 Current Transformer Type (TypCt) . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3.1.1 Basic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3.1.2 Additional data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3.1.3 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3.2 Current Transformer (StaCt) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3.2.1 Basic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3.2.2 Additional Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
3.2.3 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
4 Transfer functions
4.1
4
Load Flow, Short-circuit and RMS simulation Model . . . . . . . . . . . . . . . .
4
4.1.1 CT with Y connection on secondary side . . . . . . . . . . . . . . . . . . .
5
4.1.2 CT with D connection on the secondary side . . . . . . . . . . . . . . . .
5
4.2 EMT simulation Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
4.2.1 CT with Y connection on secondary side . . . . . . . . . . . . . . . . . . .
7
4.2.2 CT with D connection on secondary side . . . . . . . . . . . . . . . . . .
7
5 Ct saturation models
8
5.0.3 Piecewise Linear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
5.0.4 Polynomial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
A Parameter Definitions
10
A.1 Current Transformer Type (TypCt) . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
A.2 Current Transformer (StaCt ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
B Signal Definitions
B.1 Single phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Contents
B.2 3 phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
List of Figures
12
List of Tables
13
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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.
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Current Transformer (StaCT)
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3
Features & User interface
3
3.1
3.1.1
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
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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.
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Current Transformer (StaCT)
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4
Transfer functions
4
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.
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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
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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)
I1x
ratio
I20x =
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 =
curmg
ωN
Zbnom
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Current Transformer (StaCT)
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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:
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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)).
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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)).
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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.
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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
10
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)
DIgSILENT PowerFactory 2016, Technical Reference
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
11
List of Figures
List of Figures
2.1 DIgSILENT The Current Transformer “StaCt” 3 phase connection scheme with
the measurement element. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2.2 DIgSILENT The Current Transformer “StaCt” single phase connection scheme
with the measurement element. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
4.1 DIgSILENT The Current Transformer “StaCt” LDF, Short Circuit, RMS model. . .
4
4.2 DIgSILENT The Current Transformer “StaCt” EMT simulation model. . . . . . . .
6
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Current Transformer (StaCT)
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List of Tables
List of Tables
A.1 Input parameters of Ct type (TypCt) . . . . . . . . . . . . . . . . . . . . . . . . .
10
A.2 Input parameters of Ioc element (RelIoc )) . . . . . . . . . . . . . . . . . . . . . .
10
B.1 Input/output signals of the single phase StaCt element (CalStaCt1p) . . . . . . .
11
B.2 Input/output signals of 3 phase Current Transformer element (CalStaCt) . . . . .
11
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Current Transformer (StaCT)
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