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Introduction

Power-flow solves for voltage magnitude and voltage angle of the load buses as well as reactive power of the generators to satisfy energy balance throughout the power system. The feature is active only if the corresponding key is in the license.

The power-flow feature in ePHASORSIM is for both balanced systems (positive sequence) that include models of machines and also three-phase unbalance systems which include voltage sources. The input data format can be either Excel (v1.3 or later), PSS/E (v.32) or CYME. It assumes that taps of transformers and switchable shunt devices are locked.

Power-flow executes only on the host machine (offline) but the results can be used as input for real-time simulation (and it has no impact on the runtime performance).

Power-flow uses the Newton-Raphson algorithm. It takes the base power value (MVA) from the network data and the other required parameters such as the maximum number of iterations and tolerance from the Simulink mask.

Running Power-Flow

The power-flow feature can be executed from the Simulation settings tab inside ePHASORSIM's Simulink mask using the Execute or Execute and export report buttons (discussed in detail in section Simulation settings).

If the Start from Power-flow is selected, the power-flow algorithm runs just after pressing the Run simulation button in the Simulink window. The following files will be created after the power-flow algorithm has run:

  • [XLS file name]_solver_powerflow.opal: This file is created if the power-flow algorithm converges. It is the same as [XLS file name]_solver.opal except that bus voltage as well as machine reactive power values are updated with the power-flow results.
  • [XLS file name]_powerflow.state: This file is used by ePHASORsim to store information about the power-flow computation across simulations. It is not to be modified by hand.



Note: If the power-flow solution results in the voltage magnitude on some buses to be out of [0.8-1.2] p.u. range, a warning message indicating voltage violation is shown.



Island Detection Function

Island detection function is available in ePHASORsim for users’ convenience to find out the islands in the network. It will generate a '*.txt' report to show how many islands are there in the network. If there are multiple islands in the network, the user should add one slack bus to each island in order to run the power-flow.

Initialization Methods

From input data

Power-flow algorithm can be configured to start with the values specified in the network input data file.

Flat Start

The user can run power-flow algorithm with flat start, i.e. the initial voltage magnitude of all PQ buses are assumed to be equal to 1 p.u. and also initial voltage angle of all the buses to be equal to 0 degrees.

Smart Start

Power-flow algorithm can start with smart start, i.e. a linear approximation of the power-flow equations is solved in prior to provide a good initial guess to the Newton-Raphson method.

Supported Components

Positive Sequence

The table below lists the positive sequence components supported by the Power-Flow.

Component

Excel v1.4 or later

PSS/e version 32

Machine*

built-in library

All types of machines in Native Library

GENCLS, GENROU, GENROE, GENSAL, GENSAE

Modelica based library

GENCLS, GENROU, GENSAL, GENROE, GENSAE, CSVGN5

Load

All types of loads in Native Library

Constant Power Load, Constant Impedance Load & Constant Cur­rent Load

Voltage source*

Voltage source

-

Branch

All types of line in in Native Library

Supported

Switch

Switch

-

Fixed shunt

-

Supported

Transformer

All types of transformer in Native Library

Both 2-Winding and 3-Winding transformers are supported but con­trol mode is considered to be zero (COD1=COD2=CODE3=0)

Switched shunt

-

Supported but the control mode is considered to be zero (MODSW=0)

FACTS*

Modelica based library

-

Only FACTS device with shunt ele­ment is supported (J=0).

Two terminal DC line

Modelica based library

Supported but the firing angle limits are not con­sidered.

Supported but the firing angle limits are not considered.


Note: 

  • Voltage set-point of Machine, FACTS and Voltage source is read from initial voltage magnitude field of the connected bus, in the bus data record section.
  • The voltage source supported in the *.xls format will be treated as a slack bus in the power-flow calculation.
  • To be able to run power-flow for a data which uses FMUs:
    • GenUnits must have parameters ‘P_gen’, ‘Q_gen’, ‘Vt_abs’, ‘Vt_ang’ defined. These parameters should be also declared in FMUGloassary with the same name if importing data from PSS/e, PowerFactory or CYME.
    • If data is imported from Excel file, parameters 'Qmin' and 'Qmax' must be defined in the corresponding Excel sheet for the GenUnit.
    • Two terminal DC line FMU must have the following fields: ‘NBR’, ‘RCR’, ‘XCR’, ‘EBASR’, ‘TRR’, ‘TAPR’, ‘NBI’, ‘RCI’, ‘XCI’, ‘EBASI’, ‘TRR’, ‘TAPI’, ‘SETVL’, ‘RCOMP’, ‘VSCHED’, ‘RDC’, ‘Vmag_rec’, ‘Vmag_inv’, ‘Vang_rec’, ‘Vang_inv’.


Multi-Phase

The table below lists the three-phase components supported by the Power-Flow.

Component

Excel v1.5 or later

CYME

Comments

Three Phase Volt­age source

Supported**

Source Node

The connected bus should be defined as SLACK bus

Multi-Phase ZIP Load

Supported

Spot Load, Distributed Load, ECG

wye configuration only

Multi-Phase PI Line

Supported

Busway, Cable, Over­head line

-

Three Phase transformer

Supported

Transformer, Regulator

-

Switch

Supported

Switch, Breaker, Recloser

-

Multi-Phase ShuntSupported--


Note: **For three phase voltage sources, the voltage magnitude and angle set-points are read from bus page of the Excel file.


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