PSS®E

PSS®E software from Siemens provides analysis functions for power system networks in steady-state and dynamic conditions. PSS®E uses different types of files to exchange data about the network. One of them is the RAW file (power flow data file). A PSS®E RAW file contains a collection of unprocessed data that specifies a Bus/Branch network model for the establishment of a power flow working case.

The RAW file has multiple groups of records (data blocks), with each group containing a particular type of data needed in power flow. The last record of each data block is a record specifying a value of zero to indicate the end of the category.

Each record in a data block contains a set of data items separated by a comma or one or more blanks where alphanumeric attributes must be enclosed in single quotes. As many of the data items specified in the RAW file have a default value only the specific information needed should be defined in the record.

In PSS®E version 35 a new RAWX file format (Extensible Power Flow Data File) based on JSON has been introduced. It will be the standard text-based data format for PSS®E power flow data exchange. The RAWX files contain two types of data objects: Parameter Sets and Data Tables. A Parameter Set has an array with field names and a single array with field values. A Data Table has an array with field names an and array of records, each record being an array of field values. The field names array indicates the order and subset of fields for which data is provided in the data arrays.

A minimum network model is included as an example in version 35 of both formats RAW and RAWX.

 0,      100.0, 35, 0, 0, 60.00       / October 27, 2020 18:37:53
 PSS(R)E Minimum RAW Case

0 / END OF SYSTEM-WIDE DATA, BEGIN BUS DATA
    1,'Slack-Bus   ', 138.0000,3
    2,'Load-Bus    ', 138.0000,1
0 / END OF BUS DATA, BEGIN LOAD DATA
    2,'1 ',1,,,   40.000,    15.000
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
    1,'1 ',   40.350,   10.870
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
    1,     2,'1 ', 0.01938, 0.05917,0.05280
0 / END OF BRANCH DATA, BEGIN SYSTEM SWITCHING DEVICE DATA
0 / END OF SYSTEM SWITCHING DEVICE DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
0 / END OF AREA DATA, BEGIN TWO-TERMINAL DC DATA
0 / END OF TWO-TERMINAL DC DATA, BEGIN VOLTAGE SOURCE CONVERTER DATA
0 / END OF VOLTAGE SOURCE CONVERTER DATA, BEGIN IMPEDANCE CORRECTION DATA
0 / END OF IMPEDANCE CORRECTION DATA, BEGIN MULTI-TERMINAL DC DATA
0 / END OF MULTI-TERMINAL DC DATA, BEGIN MULTI-SECTION LINE DATA
0 / END OF MULTI-SECTION LINE DATA, BEGIN ZONE DATA
0 / END OF ZONE DATA, BEGIN INTER-AREA TRANSFER DATA
0 / END OF INTER-AREA TRANSFER DATA, BEGIN OWNER DATA
0 / END OF OWNER DATA, BEGIN FACTS CONTROL DEVICE DATA
0 / END OF FACTS CONTROL DEVICE DATA, BEGIN SWITCHED SHUNT DATA
0 / END OF SWITCHED SHUNT DATA, BEGIN GNE DEVICE DATA
0 / END OF GNE DEVICE DATA, BEGIN INDUCTION MACHINE DATA
0 / END OF INDUCTION MACHINE DATA, BEGIN SUBSTATION DATA
0 / END OF SUBSTATION DATA
Q
{
     "network":{
         "caseid":{
             "fields":["ic", "sbase", "rev", "xfrrat", "nxfrat", "basfrq", "title1"],
             "data":[0, 100.00, 35, 0, 0, 60.00, "PSS(R)E Minimum RAWX Case"]
         },
         "bus":{
             "fields":["ibus", "name", "baskv", "ide"],
             "data":[
                 [1, "Slack-Bus", 138.0, 3],
                 [2, "Load-Bus", 138.0 1]
             ]
         },
         "load":{
             "fields":["ibus", "loadid", "stat", "pl", "ql"],
             "data":[
                 [2, "1", 1, 40.0, 15.0]
             ]
         },
         "generator":{
             "fields":["ibus", "machid", "pg", "qg"],
             "data":[
                 [1, "1", "40.35", "10.87"]
             ]
         },
         "acline":{
             "fields":["ibus", "jbus", "ckt", "rpu", "xpu", "bpu"],
             "data":[
                 [1, 2, "1", 0.01938, 0.05917, 0.05280]
             ]
         }
    }
}

Import

The import module reads and converts a PSS®E power flow data file to the PowSyBl grid model. The current implementation supports RAW format for versions 33 and 35 and RAWX format for version 35. The import process is performed in three steps:

  • Read input file.
  • Validate input data.
  • Convert input data into PowSyBl grid model.

First, input data is obtained by reading and parsing the input file and as result a PSS®E model is created in memory. This model can be viewed as a set of Java classes where each data block of the PSS®E model is associated with a specific Java class that describes all their attributes or data items. Then, some inconsistency checks are performed on this model. If the validation succeeds the PSS®E model is converted to a PowSyBl grid model.

Options

Parameters for the import can be defined in the configuration file in the import-export-parameters-default-value module.

psse.import.ignore-base-voltage
The psse.import.ignore-base-voltage property is an optional property that defines if the importer should ignore the base voltage information present in the PSS®E file. The default value is false.

Inconsistency checks

-TODO

Conversion

A PSS®E file specifies a Bus/Branch network model where typically there is a bus for each voltage level inside a substation and where substation objects are not explicitly defined. Breakers and switches were traditionally modeled as zero impedance lines with special identifiers. Since version 35 PSS®E supports explicit definition of substation data and switching devices at both system and substation level. However, this information is optional and may not be present in the case.

The PowSyBl grid model establishes the substation as a required container of voltage levels and equipments. The first step in the conversion process assigns a substation for each PSS®E bus, ensuring that all buses at transformer ends are kept in the same substation.

The current conversion does not use explicit PSS®E substation information. Instead, buses are grouped using zero impedance branches and transformers as connectors. A new voltage level is created for each group of buses connected by zero impedance branches, and a new substation is created for the voltage levels connected by transformers. Explicit substations will be supported in future versions, allowing to represent the internal connectivity.

In the PowSyBl grid model all the network components are identified through a global and unique alphanumeric identifier (Id). Optionally, they may receive a name (Name).

For each substation the following attributes are defined:

  • Id following the pattern S<n> where n represents a consecutive integer number starting from 1.

Every voltage level is assigned to its corresponding substation, with attributes:

  • Id following the pattern VL<n> where n represents the minimum PSS®E bus number included inside the voltage level.
  • NominalV Nominal voltage of the voltage level. Equal to 1 if psse.import.ignore-base-voltage property is true. Otherwise, it is assigned to the base voltage of one representative bus inside the voltage level, read from PSS®E field BASKV.
  • TopologyKind Topology level assigned to the network model, always BUS_BREAKER.

The following sections describe in detail how each supported PSS®E data block is converted to PowSyBl network model objects.

Bus Data

There is a one-to-one correspondence between the records of the PSS®E Bus Data block and the buses of the PowSyBl network model. For each record in the Bus Data block a PowSyBl bus is created and assigned to its corresponding voltage level with the following attributes:

  • Id according to the pattern B<n> where n represents the PSS®E bus number (field I in the Bus Data record).
  • Name is copied from PSS®E field NAME.
  • V is obtained from the PSS®E bus voltage magnitude, VM, multiplied by the nominal voltage of the corresponding voltage level.
  • Angle is copied from the PSS®E bus voltage phase angle, VA.

Load Data

Every Load Data record represents one load. Multiple loads are allowed at the same bus by specifying one Load Data record with the same bus and different load identifiers. Each record defines a new load in the PowSyBl grid model associated with its corresponding voltage level and with the following attributes:

  • Id according to the pattern <n>-L<m> where n represents the PSS®E bus number (field I in the Load Data record) and m is the PSS®E alphanumeric load identifier (field ID in the Load Data record).
  • ConnectableBus PowSyBl bus identifier assigned to the PSS®E bus number (field I in the Load Data record).
  • P0 Active power. It is copied from PSS®E field PL.
  • Q0 Reactive power. It is copied from PSS®E field QL.

The load is connected to the ConnectableBus if load status (field STATUS in the Load Data record) is 1 (In-service).

PSS®E supports loads with three different characteristics: Constant Power, Constant Current and Constant Admittance. The current version only takes into consideration the Constant Power component, discarding the Constant Current component (fields IP and IQ in the Load Data record) and the Constant Admittance component (fields YP and YQ in the Load Data record).

Fixed Bus Shunt Data

Each Fixed Bus Shunt Data record defines a PowSyBl shunt compensator with a linear model and a single section. It is possible to define multiple fixed shunts at the same bus. The PowSyBl shunt compensator is associated with its corresponding voltage level and has the following attributes:

  • Id according to the pattern <n>-SH<m> where n represents the PSS®E bus number (field I in the Fixed Bus Shunt Data record) and m is the PSS®E alphanumeric shunt identifier (field ID in the Fixed Bus Shunt Data record).
  • ConnectableBus PowSyBl bus identifier assigned to the PSS®E bus number (field I in the Fixed Bus Shunt Data record).
  • SectionCount Always 1.
  • gPerSection Positive sequence shunt (charging) conductance per section. It is defined as GL / (vnom *vnom), where GL is the active component of shunt admittance to ground, entered in MW at one per unit voltage (field GL in the Fixed Bus Shunt Data record) and vnom is the nominal voltage of the corresponding voltage level.
  • bPerSection Positive sequence shunt (charging) susceptance per section. It is defined as BL / (vnom *vnom), where BL is the reactive component of shunt admittance to ground, entered in MVAR at one per unit voltage (field BL in the Fixed Bus Shunt Data record).
  • MaximumSectionCount Always 1.

The shunt compensator is connected to the ConnectableBus if fixed shunt status (field STATUS in the Fixed Bus Shunt Data record) is 1 (In-service).

Switched Shunt Data

In the PSS®E version 33 only one switched shunt element can be defined at each bus. Version 35 allows multiple switched shunts at the same bus, adding an alphanumeric switched shunt identifier.

A switched shunt device may be a mix of reactors and capacitors; it is divided in blocks and steps: a block contains n steps of the same admittance. The steps and blocks can be adjusted to regulate a given magnitude: a voltage at a bus, a reactive power output or an admittance. Only voltage regulation is considered when mapping this equipment to PowSyBl.

There are two methods for defining how a switched shunt steps and blocks should be adjusted to keep the controlled magnitude between limits; the method chosen is determined by the field ADJM in the Switched Shunt Data record. If ADJM is 0 steps and blocks are switched on in input order, and switched off in reverse output order. If ADJM is 1, steps and blocks are switched on and off such that the next highest (or lowest, as appropriate) total admittance is achieved.

Each switched shunt record defines a PowSyBl shunt compensator with a non-linear model with the following attributes:

  • Id according to the pattern <n>-SwSH<m> where n represents the PSS®E bus number (field I in the Switched Shunt Data record) and m is the PSS®E alphanumeric shunt identifier (field ID in version 35 of the Switched Shunt Data record, forced to "1" when importing version 33 data).
  • ConnectableBus PowSyBl bus identifier assigned to the PSS®E bus number (field I in the Switched Shunt Data record).
  • SectionCount Defined as the section count (section index + 1) where section B is closer to the initial switched shunt admittance (field BINIT in the Switched Shunt Data record).
  • TargetV Voltage setpoint defined as 0.5 * (VSWLO + VSWHI) * vnom, where VSWLO is the controlled voltage lower limit (field VSWLO in the Switched Shunt Data record) and VSWHI is the controlled voltage upper limit (field VSWHI in the Switched Shunt Data record).
  • TargetDeadband defined as (VSWHI - VSWLO) * vnom.
  • RegulatingTerminal Regulating terminal assigned to the bus where voltage is controlled by this switched shunt (field SWREM in version 33 or field SWREG in version 35, both in the Switched Shunt Data record if they are not 0. Otherwise field I in the Switched Shunt Data record).
  • VoltageRegulatorOn defined as true if the control mode is not 0 (field MODSW in the Switched Shunt Data record) and TargetV is greater than 0.0.

The shunt compensator is connected to the ConnectableBus if switched shunt status (field STAT in the Switched Shunt Data record) is 1 (In-service).

The sections of the PowSyBl shunt compensator non-linear model are defined according to the adjustment method of the PSS®E switched shunt. In the PowSyBl model, the susceptance at each section is the accumulated susceptance obtained if the section and all previous ones are connected.

The attributes of each section in the PowSyBl shunt compensator non-linear model are defined as:

  • Section G Positive sequence shunt (charging) conductance of this section. Always 0.0.
  • Section B Positive sequence shunt (charging) susceptance of this section. It is defined as B / (vnom *vnom), where B is the reactive component of shunt admittance to ground, entered in MVAR at one per unit voltage assigned to this section and vnom is the nominal voltage of the corresponding voltage level.

When the adjustment method ADJM is 0, the behaviour of the switched shunt can be mapped directly to the shunt compensator non-linear model with sections based on the switched shunt blocks/steps and its order in the [email protected] input record. A section is assigned to each step of the reactor and capacitor shunt blocks by accumulating the admittance of the corresponding steps that are in-service. Only the in-service switched shunt blocks are considered (field SI in version 35 of the Switched Shunt Data record, always in-service in version 33). A section with 0.0 susceptance is added between sections assigned to reactor and capacitor blocks.

If the adjustment method ADJM is 1, the reactor and capacitor blocks can be specified at any order, and all the switching combinations are considered in PSS®E. Current conversion does not support building a separate section for each switching combination. To map the [email protected] shunt blocks/steps into PowSyBl sections, first the reactor and capacitor blocks are increasingly ordered by susceptance (field BI in the Switched Shunt Data record) and then sections are created like in the previous adjustment considering that blocks are switched on following the sorted order.

Generator Data

Every Generator Data single line record represents one generator. Multiple generators are allowed at a PSS®E bus by specifying the same bus and a different identifier. Each record defines a new generator in the PowSyBl grid model associated with its corresponding voltage level and with the following attributes:

  • Id according to the pattern <n>-G<m> where n represents the PSS®E bus number (field I in the Generator Data record) and m is the PSS®E alphanumeric load identifier (field ID in the Generator Data record).
  • ConnectableBus PowSyBl bus identifier assigned to the PSS®E bus number (field I in the Generator Data record).
  • TargetP Active power. It is copied from PSS®E field PG.
  • MinP Minimum generator active power. It is copied from PSS®E field PB.
  • MaxP Maximum generator active power. It is copied from PSS®E field PT.
  • TargetQ Reactive power. It is copied from PSS®E field QG.
  • MinQ Minimum generator reactive power. It is copied from PSS®E field QB.
  • MaxQ Maximum generator reactive power. It is copied from PSS®E field QT.
  • TargetV Voltage setpoint defined as VS * vnom, where VS is the regulated voltage (field VS in the Generator Data record) and vnom is the nominal voltage of the corresponding voltage level.
  • RegulatingTerminal Regulating terminal assigned to the bus where voltage is controlled by this generator (field IREG in the Generator Data record if it is not 0. Otherwise field I in the Generator Data record).
  • VoltageRegulatorOn defined as true if the type code of the associated bus is 2 or 3 (field IDE in the Bus Data record) and TargetV is greater than 0.0 and MaxQ is greater than MinQ.

The generator is connected to the ConnectableBus if generator status (field STAT in the Generator Data record) is 1 (In-service).

Non-Transformer Branch Data

In PSS®E each AC transmission line is represented as a non-transformer branch record and defines a new line in the PowSyBl grid model with the following attributes:

  • Id according to the pattern L-<n>-<m>-<p> where n represents the PSS®E bus 1 number (field I in the Non-Transformer Branch Data record), m represents the bus 2 number (field J in the Non-Transformer Branch Data record) and p is the circuit identifier (field CKT in the Non-Transformer Branch Data record).
  • ConnectableBus1 PowSyBl bus identifier assigned to the PSS®E bus 1 number (field I in the Non-Transformer Branch Data record).
  • VoltageLevel1 PowSyBl voltage level assigned to the bus 1.
  • ConnectableBus2 PowSyBl bus identifier assigned to the PSS®E bus 2 number (field J in the Non-Transformer Branch Data record).
  • VoltageLevel2 PowSyBl voltage level assigned to the bus 2.
  • R Resistance defined as R * vnom2 * vnom2 / sbase where R is the resistance of the branch (field R in the Non-Transformer Branch Data record), vnom2 is the nominal voltage of the voltage level assigned to the bus 2 and sbase is the system MVA base (field SBASE in the Case Identification Data record).
  • X Reactance defined as X * vnom2 * vnom2 / sbase where X is the reactance of the branch (field X in the Non-Transformer Branch Data record).
  • G1 Conductance of the line shunt at the bus 1 defined as (GI * sbase) / ( vnom2 * vnom2) where GI is the conductance at the bus 1 (field GI in the Non-Transformer Branch Data record).
  • B1 Susceptance defined as (( 0.5 * B + BI ) * sbase) / ( vnom2 * vnom2) where B is the total branch charging susceptance (field B in the Non-Transformer Branch Data record) and BI is the susceptance at the bus 1 (field BI in the Non-Transformer Branch Data record).
  • G2 Conductance of the line shunt at the bus 2 defined as (GJ * sbase) / ( vnom2 * vnom2) where GJ is the conductance at the bus 2 (field GJ in the Non-Transformer Branch Data record).
  • B2 Susceptance defined as (( 0.5 * B + BJ ) * sbase) / ( vnom2 * vnom2) where B is the total branch charging susceptance (field B in the Non-Transformer Branch Data record) and BJ is the susceptance at the bus 2 (field BJ in the Non-Transformer Branch Data record).

The line is connected at both ends if the branch status (field ST in the Non-Transformer Branch Data record) is 1 (In-service).

A set of current permanent limits is defined as 1000.0 * rateMva / (sqrt(3.0) * vnom1) at the end 1 and 1000.0 * rateMva / (sqrt(3.0) * vnom2) at the end 2 where rateMva is the first rating of the branch (field RATEA in version 33 of the Non-Transformer Branch Data record and field RATE1 in version 35) and vnom1 and vnom2 are the nominal voltages of the associated voltage levels.

Transformer Data

The Transformer Data block defines two windings and three windings transformers. Two windings transformers have four line records, while three windings transformers have five line records. A 0 value in the field K of the Transformer Data record first line is used to indicate that is a two windings transformer, otherwise is considered a three windings transformer.

[email protected] two windings transformer records are mapped to two windings transformers in the PowSyBl grid model. They are associated with corresponding voltage levels inside the same substation and defined with the following attributes:

  • Id according to the pattern T-<n>-<m>-<p> where n represents the PSS®E bus 1 number (field I in the Transformer Data record), m represents the bus 2 number (field J in the Transformer Data record) and p is the circuit identifier (field CKT in the Transformer Data record).
  • ConnectableBus1 PowSyBl bus identifier assigned to the PSS®E bus 1 number (field I in the Transformer Data record).
  • VoltageLevel1 PowSyBl voltage level assigned to the bus 1.
  • ConnectableBus2 PowSyBl bus identifier assigned to the PSS®E bus 2 number (field J in the Transformer Data record).
  • VoltageLevel2 PowSyBl voltage level assigned to the bus 2.
  • RatedU1 Rated voltage at the end 1. The nominal voltage of the associated voltageLevel is assigned.
  • RatedU2 Rated voltage at the end 2. The nominal voltage of the associated voltageLevel is assigned.
  • R Transmission resistance.
  • X Transmission reactance.
  • G Shunt conductance.
  • B Shunt susceptance.
  • TapChanger Could be a ratio tap changer o a phase tap changer.
  • OperationalLimits Current limits for both ends.

The transformer is connected at both ends if the branch status (field STAT in the Transformer Data record) is 1 (In-service)

In PSS®E the transformer model allows to define a ratio and angle at the end 1 and only a fixed ratio at the end 2. The transformer magnetizing admittance is modeled between the bus and the ratio of the end 1. The PowSyBl grid model supports a ratioTapChanger and a phaseTapChanger at the end 1 and the magnetizing admittance is between the ratio and the transmission impedance.

TwoWindingsTransformerModels

To express the PSS®E electric attributes of the transformer in the PowSyBl grid model the following conversions are performed:

  • The first step is to define the complex impedance between windings (Z) by using the resistance and reactance (fields R1-2 and X1-2 in the Transformer Data record), the winding base MVA (field SBASE1-2 in the Transformer Data record) and the system MVA base (field SBASE in the Case Identification Data record) according to the code that defines the units in which the winding impedances R1-2, X1-2 are specified (field CZ in the Transformer Data record). Then the complex impedance (Z) is converted to engineering units using the nominal voltage of the voltage level at end 2 and the system MVA base. Finally it should be adjusted after fixing an ideal ratio at end 2 and moving the configured ratio to the end 1. The obtained result is assigned to the transmission resistance and reactance of the PowSyBl transformer.

  • The complex shunt admittance Ysh is calculated using the transformer magnetizing admittance connected to ground at bus 1 (fields MAG1 and MAG2 in the Transformer Data record), the winding base MVA (field SBASE1-2 in the Transformer Data record), the system MVA base, the bus base voltage (field BASKV in the Bus Data record) of the transformer bus I and the nominal (rated) winding 1 voltage base (field NOMV1 in the Transformer Data record) according to the magnetizing admittance code that defines the units in which MAG1 and MAG2 are specified (filed CM in the Transformer Data record). The next step is to convert the complex Ysh to engineering units using the nominal voltage of the voltage level at end 2 and the system MVA base and finally the obtained value is assigned to the shunt conductance and susceptance of the PowSyBl transformer. The shunt conductance in the PowSyBl grid model is located after the ratio so is necessary to add a step correction by each different ratio in the tabular tapChanger.

To define the tapChanger the first step is to calculate the complex ratio at end 1 and the ratio at end 2. The ratio at end 1 is calculated using the winding ratio (field WINDV1 in the Transformer Data record), the nominal (rated) winding voltage base (field NOMV1 in the Transformer Data record) and the bus base voltage (field BASKV in the Bus Data record) according to the code that defines the units in which the turns ratios are specified (field CZ in the Transformer Data record). The angle at end 1 is copied from the winding phase shift angle (field ANG1 in the Transformer Data record). The ratio at end 2 is calculated in the same way as at end 1 but using the following fields (fields WINDV2, NOMV1 in the Transformer Data record) and the corresponding bus base voltage at bus J (field BASKV in the Bus Data record).
Then a tapChanger at end 1 is defined by fixing one of the components of the complex ratio at end 1 and moving the other in each step using the number of tap positions available (field NTP1 in the Transformer Data record) and the upper and lower limits (fields RMA1, RMI1 in the Transformer Data record).
Finally, the tapChanger is adjusted twice, after fixing an ideal ratio at end 2 by moving the current ratio to end 1 and after moving the shunt admittance adding in this last case a step correction for each step of the tapChanger. The tap for which the (ratio, angle) is closer to the complex ratio at end 1 is assigned as tapPosition.
This current version does not consider the impedance correction table if this transformer impedance is to be a function of either off-nominal turns ratio or phase shift angle.

If the tapChanger is a ratioTapChanger and the the transformer control mode (field COD in the Transformer Data record) is 1 a voltage control with the following attributes is defined:

  • TargetV Voltage setpoint defined as 0.5 * (VMI + VMA) * vnom, where VMA and VMI are the voltage upper and lower limits (fields VMA1, VMA1 in the Transformer Data record) and vnom is the nominal voltage of the voltageLevel at end 1.
  • TargetDeadband defined as (VMA - VMI) * vnom.
  • RegulatingTerminal Regulating terminal assigned to the bus where voltage is controlled (field CONT1 in the Transformer Data record).
  • RegulatingOn defined as true if TargetV and TargetDeadBand are greater than 0.0.

If the PSS®E transformer is controlling the reactive power (field COD = 2 in the Transformer Data record) the control is discarded as the current version of PowSyBl does not support reactive control for transformers.

When the tapChanger is a phaseTapChanger and the transformer control mode (field COD in the Transformer Data record) is 3 an active power control with the following attributes is defined:

  • TargetValue Active power flow setpoint defined as 0.5 * (APFI + APFA), where APFA and APFI are the active power flow upper and lower limits (fields VMA1, VMA1 in the Transformer Data record, same fields as voltage control).
  • TargetDeadband defined as (APLA - APFI).
  • RegulatingTerminal Regulating terminal assigned to the bus where active power flow is controlled (field CONT1 in the Transformer Data record).
  • RegulatingOn defined as true if TargetV is greater than 0.0.

A set of current operational limits is defined for the two windings transformer as 1000.0 * rateMva / (sqrt(3.0) * vnom1) at the end 1 and 1000.0 * rateMva / (sqrt(3.0) * vnom2) at the end 2 where rateMva is the first rating of the transformer (field RATA1 in version 33 of the Transformer Data record and field RATE11 in version 35) and vnom1 and vnom2 are the nominal voltage of the associated voltage levels.

When a three windings transformer is modeled the two windings transformer steps should be followed for each leg of the transformer taking into account the following considerations:

  • The Id is defined according to the pattern T-<n>-<m>-<o>-<p> where n represents the PSS®E bus 1 number (field I in the Transformer Data record), m represents the bus 2 number (field J in the Transformer Data record), o represents the bus 3 number (field K in the Transformer Data record) and p is the circuit identifier (field CKT in the Transformer Data record).
  • The three windings transformer is modeled in PowSyBl as three two windings transformers connected to an fictitious bus defined with a nominal base voltage and rated voltage of 1.0 kV (star configuration).
  • In PSS®E the between windings transmission impedances Z1-2, Z2-3 and Z3-1 are specified in the input file. These impedances are generally supplied on a transformer data sheet or test report. The transmission impedances Z1, Z2 and Z3 of the star network equivalent model are related to them according to the following expressions (see Modeling of Three-Winding Voltage Regulating Transformers for Positive Sequence Load Flow Analysis in PSS®E):

    Z1-2 = Z1 + Z2

    Z2-3 = Z2 + Z3

    Z3-1 = Z3 + Z1

    So:

    Z1 = 0.5 * (Z1-2 + Z3-1 - Z2-3)

    Z2 = 0.5 * (Z1-2 + Z2-3 - Z3-1)

    Z3 = 0.5 * (Z2-3 + Z3-1 - Z1-2)

  • All the shunt admittances of the three windings transformer in the PSS®E model are assigned to the winding 1. There is not shunt admittance at windings 2 and 3.
  • Each winding can have a complex ratio and a ratioTapChanger or phaseTapChanger with its corresponding control, always at end 1. The current PowSyBl version only supports one enabled control by three windings transformer so if there is more than one enabled only the first (winding 1, winding 2, winding 3) is kept enabled, the rest are automatically disabled.
  • In three windings transformers the status attribute (field STAT in the Transformer Data record) could be 0 that means all the windings disconnected, 1 for all windings connected, 2 for only the second winding disconnected, 3 for the third winding disconnected and 4 for the first winding disconnected.

ThreeWindingsTransformerModels

Slack bus

The buses defined as slack terminal are the buses with type code 3 (field IDE in the Bus Data record).

Export

The export of PowSyBl networks to PSS®E format is not yet supported.