Page Content

1 Introduction
2 Running Power-Flow
3 Island Detection Function
4 Initialization Methods
- 4.1 From input data
- 4.2 Flat Start
- 4.3 Smart Start
5 Supported Components
- 5.1 Positive Sequence
- 5.2 Multi-Phase

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. It assumes that taps of transformers and switchable shunt devices are locked.

The power-flow feature in ePHASORSIM is for both balanced systems (positive sequence) that include models of machines and also three-phase unbalanced systems which include voltage sources. Unbalanced power-flow is only available for networks defined in Excel (v1.8 or later) or CYME.

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 v32

Component		Excel v1.4 or later	PSS/E v32
Machine*	Built-in native library	All types of machines in Native Library	GENCLS, GENROU, GENROE, GENSAL, GENSAE
Machine*	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.

Notes

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

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 Shunt	Supported	-	-

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