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ETAP PowerStation 4.0

User Guide

Copyright 2001 Operation Technology, Inc.

All Rights Reserved This manual has copyrights by Operation Technology, Inc. All rights reserved. Under the copyright laws, this manual may not be copied, in whole or in part, without the written consent of Operation Technology, Inc. The Licensee may copy portions of this documentation only for the exclusive use of Licensee. Any reproduction shall include the copyright notice. This exception does not allow copies to be made for other persons or entities, whether or not sold. Under this law, copying includes translating into another language. Certain names and/or logos used in this document may constitute trademarks, service marks, or trade names of Operation Technology, Inc. or other entities. • Access, Excel, ODBC, SQL Server, Windows NT, Windows 2000, Windows Me, Windows

98, Windows XP, and Microsoft Word are registered trademarks of Microsoft Corporation. • AutoCad is a registered trademark of Autodesk. • Oracle is a registered trademark of Oracle Corporation. • PowerPlot is a registered trademark of Jackson & Associates. • Crystal Reports is a registered trademark of Seagate Software. • MATLAB and Simulink are registered trademarks of MathWorks • Screen shot(s) reprinted by permission from Microsoft Corporation. Operation Technology, Inc. believes that the information contained herein is accurate as of its publication date, and such information is subject to change without notice. This information is provided “as is” without warranty of any kind, either expressed or implied, including but not limited to the implied warranties of merchantability, fitness for a particular purpose, or non-infringement. Operation Technology, Inc. assumes no responsibility for errors or omissions in this publication or any other documents referenced in this publication.

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Chapter 22

Optimal Power Flow Analysis

The PowerStation Optimal Power Flow (OPF) program is an extremely powerful simulation software for power system design, planning, and operation. It solves power system load flow, but at the same time can optimize system operating conditions and automatically adjust control variable settings, while ensuring both equality and inequality constraints are not violated. The optimized system will reduce the installation and/or operating cost, improves its overall performance, and increases its reliability and security. Besides minimizing the operating and installation cost, the program also provides a variety of other choices of optimization objectives, which covers virtually all the optimization criteria for a real power system. Any practical control means in a power system such as transformer LTC, generator AVR control, shunt and series compensations, and load shed can all be considered in the calculation. Constraints for bus voltage, branch flow in different types (MVA, MW, Mvar, and Amp), as well as control variables are also available for users to select and enforce. By using state-of-the-art optimization algorithms and advanced programming techniques, this program is proven very capable, robust, and effective. Systems with over 20,000 buses can be solved at incredible speed.

Operation Technology, Inc. 22-1 ETAP PowerStation 4.0

Optimal Power Flow Analysis Introduction

Some of the key features of the Optimal Power Flow program are summarized below: • Common & Integrated Databases • Fully Inherited 3-D Data Structure Including Infinite Presentations, Unlimited Configurations, &

Multiple Data Reversions • Handles Looped, Radial, or Combined Systems • Systems with Multiple Swing Buses • Systems with Isolated Sub-Systems • Systems with Zero Impedance Branches (Tie Circuit Breakers) • Systems with De-Energized Buses & Branches • Automatic Adjustment of Cable/Line Resistance According to Operating Temperatures • Automatic Adjustment of Transformer Impedance According to Tolerance • Automatic Adjustment of Current Limiting Reactor Impedance According to Tolerance • Choice of Loading Categories • Load Diversity Factors • Accurate AC Modeling • State-of-the-Art Interior Point Algorithm • Logarithmic Barrier Function (Handles Both Equality & Inequality Constraints) • Primal-Dual Direction Search Method • Controlled Solution Parameters • Minimize System Real Power Losses • Minimize System Reactive Power Losses • Minimize Swing Bus Power • Minimize Shunt Mvar Devices • Minimize Fuel Cost • Minimize Series Compensation • Minimize Generation Cost • Minimize Control Movement • Minimize Control Adjustment • Maximize Voltage Security Indexes • Maximize Line Flow Security Indexes • Flatten Voltage Profiles • User-Defined Objective Functions • Voltage Constraint • Line Flow Constraint • Control Limit Constraint • Generator Var Limit Constraint • Transmission Interface Limit Constraint • Smooth Function of Any Variables • Generator MW & Mvar Control • Transformer LTC Control • Transformer Phase-Shifter Control • Shunt Compensation Control • Series Compensation Control • Switching Capacitor Control


Optimal Power Flow Study Toolbar

22.1 Study Toolbar The Optimal Power Flow Study Toolbar will appear on the screen when you are in Optimal Power Flow Study mode. This toolbar has six function keys, as shown below:

Run Optimal Power Flow Display Options Report Manager

Halt Current Calculation Get On-Line Data Get Archived Data

Run Optimal Power Flow Select a study case from the Study Case Toolbar when you are in Optimal Power Flow study mode, then click on the Run Optimal Power Flow button to perform an optimal power flow study. A dialog box will appear at this time to ask you to specify the output report name if the output file name is set to Prompt in the Output Report list box. The optimal power flow study results will appear on the one-line diagram and can be viewed in the output report text format.

Display Options Click on this button to customize the one-line diagram annotation display options under the Optimal Power Flow Study mode. See Display Options for more information.

Report Manager Click on the Report Manager button to select a format and view transient stability output report. Optimal power flow analysis reports are currently provided in ASCII formats only, which can be accessed from the Report Manager.


Optimal Power Flow Study Toolbar

You can also select output files from the Output Report list box.

This list contains all the output files in the current project folder with the same file extension specified. To change output file extensions, you can click on the List Output Reports button next to the Output Report list box, which will allow you to select a different output file extension.

The output reports for optimal power flow studies have a .opr extension.

Halt Current Calculation Click on the Stop Sign button to halt the current calculation.

Get On-Line Data If the ETAP key installed on your computer has the on-line feature you can copy the on-line data from the on-line presentation to the current presentation.

Get Archived Data If the ETAP key installed on your computer has the on-line feature you can copy the archived data to the current presentation.


Optimal Power Flow Study Case Editor

22.2 Study Case Editor The Optimal Power Flow Study Case Editor contains solution control variables, objective selections, constraint settings, control variable activation, system loading conditions, and report options. PowerStation allows you to create and save an unlimited number of study cases for each type of study. Like any other study types, you can easily switch between different optimal power flow study cases. This feature is designed to organize your study efforts and save you time. A study case can be used for any combination of configuration status, one-line diagram presentation, and Base/Revision Data. To create a new optimal power flow study case, go to the Project Editor, right-click on the Optimal Power Flow sub-folder inside the Study Cases folder, and select Create New. The program will then create a new study case, which is a copy of the default study case, and adds it to the Optimal Power Flow sub-folder.

When you are in Optimal Power Flow mode, you can access the Optimal Power Flow Study Case Editor by clicking on the Study Case button on the Study Case Toolbar. You can also access this editor from the Project Editor by clicking on the Optimal Power Flow sub-folder under the Study Cases folder. The Optimal Power Flow Study Case Editor consists of the following nine pages: Info page, Objective page, LTC page, Generator AVR page, Generator MW page, Shunt Comp page, Bus Voltage Constraint page, and Branch Flow Constraint page.



22.2.1 Info Page

Study Case ID The study case ID is shown in this entry field. You can rename a study case by simply deleting the old ID and entering a new ID. The study case ID can be up to 12 alphanumeric characters. Use the Navigator button at the bottom of the editor to go from one study case to another.

Solution Parameters

Barrier Factor This is the fixed value of barrier factor used in the barrier function. It is defaulted to 0.0000001. The program starts the barrier factor at 1 and will automatically reduce it during the calculation iteration.

Power Mismatch This is the power flow mismatch. The default value is 0.001 per unit on 1 MVA base.



Max. Iteration Enter the maximum number of iterations. If the solution has not converged at the specified number of iterations, the program will stop and inform the user. The recommended and default value is 50.

Advanced Click on this button to open up the Advanced Solution Parameter Editor and set additional solution parameters for the optimal power flow study. Advanced Solution Parameter Editor Currently there is only one parameter available in this editor.

Objective Precision This parameter defines the precision for the objective function convergence. The default value is 0.001. It is recommended that you do not change this parameter in most cases.

Loading In this section of the Optimal Power Flow Study Case Editor you can specify the operating loads by selecting a loading category.

Loading Category Select one of the 10 loading categories for this study case. With the selection of any category, PowerStation uses the percent loading of individual motors and other loads as specified for the selected category. Note that you can assign loading to each one of the 10 categories in the Nameplate page, Loading page, or Rating page for most load components. Harmonic Filter loading is calculated from its parameters.

Operating Load Check this option to use operating P and Q as specified in the relevant component editors.

Charger Loading Category Select this option to use P and Q as specified in the loading category section of the Charger Editor.

Charger Operating Load Select this option to use P and Q as specified in the operating load section of the Charger Editor. Note that if this option is selected, you are required to run a DC load flow calculation first in order to estimate the charger load.



Load Diversity Factor Apply appropriate load diversity factor(s) for the system loading. The choices are:

None Select None to use the percent loading of each load as entered for the selected loading category, i.e., no diversity factor is considered.

Bus Maximum When the Bus Maximum option is selected, the loading of all motors and other loads will be multiplied by the maximum diversity factor of the bus, which they are directly connected to. Using this option, you can define the initial loading for optimal power flow studies with each bus having a different maximum diversity factor. This study option is helpful when the future loading of the electrical system has to be considered and each bus may have a different maximum diversity factor.

Bus Minimum When the Minimum option is selected, the loading of all motors and other loads will be multiplied by the bus minimum diversity factor of the bus that they are directly connected to. Using this option, you can define the initial loading for optimal power flow studies with each bus having a different minimum diversity factor. This study option may be useful in some cases where the effect of light loading conditions need to be investigated.

Global When this option is selected, PowerStation will ask you to enter global diversity factors for constant kVA and constant Z loads, respectively. When you select this option, PowerStation will globally multiply all constant kVA and constant Z loads of the selected loading category with the entered values. When using this option you can define the initial loading for transient stability analysis studies with fixed diversity factors for all loads. Note that a constant kVA load diversity factor of 125% implies that the constant kVA loads of all buses are increased by 25% above their values as specified by the selected loading category. This value can be smaller or greater than 100%.

Initial Condition This section specifies the initial voltage used for the optimal power flow study.

Use Bus Voltage Select this option to use bus voltages as specified in the Bus Editor.



Use Fixed Voltage When this option is selected, the Optimal Power Flow Study Case Editor will ask you to enter the bus voltage magnitude (in percent) and phase angle (in degree). In this case, initial values for all the buses in the system will be set to the same to have a “flat” start point.

Report The check boxes in this section are for reporting constraint violation purpose. This section is temporarily disabled.

Voltage Constraint If this box is checked, any voltage constraint violations will be reported.

Line/Transformer Constraint If this box is checked, any line flow constraint violations for cable, transmission line, transformer, reactor, and impedance will be reported.

Generator Constraint If this box is checked, any violations in generator reactive power limits will be reported.

Transformer Tap Constraint If this box is checked, any violations in transformer tap limits will be reported.

Control/Update This section is for updating the control settings from optimal power flow study results. Note that only those controls, which are activated for the present study case, will be updated if their settings are ever changed. This section is temporarily disabled.

Generator Voltage If this box is checked, the generator voltage (AVR) setting will be updated.

LTC If this box is checked, the transformer LTC settings will be updated.

Generator var If this box is checked, the generator var generation will be updated.

Generator MW If this box is checked, the generator MW generation will be updated.



Shunt Compensation If this box is checked, settings for the shunt compensation components (capacitor, etc.) will be updated.

Load Shed If this box is checked, load shed control status will be updated.

Phase Shift If this box is checked, the transformer phase shift controls will be updated. Infeasibility Handling Editor Click on the Infeasibility Handling button to open this editor.

Strategy This section provides different strategies for handling infeasibility due to various conflicts in objective functions, constraints, and power balancing equations that might be encountered during the optimal power flow calculation. The selected strategy will be automatically enforced if an infeasible condition occurs during the calculation.

Relax Generator Voltage Constraints Select this option to remove constraints on the generator voltages.

Relax Load Bus Voltage Constraints Select this option to remove constraints on the load bus voltages.

Relax All Voltage Constraints Select this option to remove voltage constraints on all buses, including the generator buses and the load buses.



Ignore and Continue Select this option to continue the optimization without any of the constraint relaxation. The calculation will continue until either a feasible solution is reached within the given number of iterations or the maximum number of iterations is reached.

Quit Calculation Select this option to quit the calculation once an infeasibility is encountered. 22.2.2 Objective Page This page is provided for you to choose the objectives for this study case.

Objective Selection Select objectives for this study case. You can select multiple objectives and use the weight factors to combine them.

Minimize Real Power Losses Select this option to minimize the real power losses in the system.

Minimize Reactive Power Losses Select this option to minimize the reactive power losses in the system.



Minimize Swing Bus Power Select this option to minimize the real power generation at the swing bus(es).

Minimize Shunt var Devices Select this option to minimize the utilization of the var generation from available shunt var control devices. Note that when this objective is selected, you must specify some shunt devices (capacitors) on the Shunt Comp page.

Minimize Fuel Cost Select this option to minimize the total generation cost from the available generators. Note that when this objective is selected, you must specify some generator MW controls on the Generator MW page.

Minimize Series Compensation Select this option to minimize the utilization of the var generation from the available series var control devices. This objective is temporarily disabled.

Minimize Load Shedding Select this option to minimize the load to be shed from the available bus load shed schedule. This objective is temporarily disabled.

Minimize Control There are two ways to minimize controls. One is to minimize control movement. In this case, the total number of controls to be adjusted is minimized. Another way is to minimize the control adjustment. In this case, the overall adjustment from all controls is minimized.

Maximize Voltage Security Index Select this option to maximize bus voltage security index. The bus voltage security index function is determined by:

n

i i

avgii

dVVV

J2Buses All

,∑

−=

where

Vi,avg = (Vi,max + Vi,min) / 2 dVi = (Vi,max – Vi,min) / 2

Maximize Line Flow Security Index Select this option to maximize line flow security index. The line flow security index function is determined by:

n

j j

j

SS

J2

Branches All

∑

=

where Sj is the line flow and jS is the line rating.

Flat Voltage Profile Select this option to optimize the system control variable settings for a flat bus voltage profile, i.e. the voltage magnitude difference for all the buses is minimum.



Weight Assign weighting factors for the each objective. A larger weighting factor represents a higher weight and will be given to its associated objective.

Exponent Variable n in the associated bus voltage and line flow index functions. 22.2.3 LTC Page This page is provided to choose the LTC controls and set their associated parameters.



Active Controls This box lists the information on all of the selected transformer LTCs, including their associated transformer ID, location (primary, secondary, or tertiary), maximum and minimum taps, and weighting factor. Only the selected LTCs are treated as active controls in the optimization process.

Select / Deselect Buttons First highlight an LTC from the box underneath the Select button. This box initially lists all the LTCs in the system for the specified Select Option. Then click on the Select button to move the highlighted LTC into the Active Controls box. Highlighting an LTC in the Active Controls box and clicking on the Deselect button will move that LTC into the box underneath the button to become an inactive control.

Selection Option Specify a category to show all the available LTCs in that category.

All / By Category Select the All option to show all the available LTCs in the system. Select the By Category option to show the available LTCs by category. Either one or any number of combinations of the categories can be chosen. For LTCs, there are two categories available: By Area and By Zone. An area number needs to be given for By Area and a zone number for By Zone. The By Category option is temporarily disabled.

Default Settings

Weight This sets the weighting factors for the selected LTC controls. You need to set the weighting factor first before you click on the Select button to activate an LTC. This number determines the weight between different LTC controls, with 100% being the maximum and highest weight.



22.2.4 Generator AVR Page This page is provided to choose the generator voltage (AVR) controls and set their associated parameters.

Active Control This box lists information on all of the selected generator AVR controls, including the generator ID, MVA rating, voltage control range, and weighting factor. Only the selected generators are treated as active controls in the optimization process.

Select / Deselect Buttons First highlight a generator from the box underneath the buttons. This box initially lists all the generators in the system for the specified Select Option. Then click on the Select button to move the highlighted generator into the Active Controls box. Highlighting a generator in the Active Controls box and clicking on the Deselect button will move that generator into the box underneath the button to become an inactive control.



Selection Option Specify a category to show all the available generators in that category.

All / By Category Select the All option to show all of the available generators in the system. Select the By Category option to show the available generators by category. Either one or any number of combinations of the categories can be chosen. For generator AVR control, there are two categories available: By Area and By Zone. An area number needs to be given for By Area and a zone number for By Zone. The By Category option is temporarily disabled.

Default Settings

Vmax / Vmin This option sets the maximum and minimum voltage limits (in %) for the selected generator AVR controls. You need to set Vmax and Vmin first before you click on the Select button to activate a generator AVR control. Weight This option sets the weighting factors for the selected generator AVR controls. You need to set the weighting factor first before you click on the Select button to activate a generator AVR control. This number determines the weight between different generator AVR controls, with 100% the maximum and the highest weight.



22.2.5 Generator MW Page This page is provided to choose the shunt compensation controls and set their associated parameters.

Active Control This box lists information on all of the selected generator/power grid MW controls, including the generator ID, MVA rating, MW control range, and weighting factor. Only the selected generators/power girds are treated as active controls in the optimization process.

Select / Deselect Buttons First highlight a generator from the box underneath the buttons. This box initially lists all the generators in the system for the specified Select Option. Then click on the Select button to move the highlighted generator into the Active Controls box. Highlighting a generator in the Active Controls box and clicking on the Deselect button will move that generator into the box underneath the button and become an inactive control.



Selection Option Specify a category to show all the available generators in that category.

All / By Category Select the All option to show all of the available generators in the system. Select the By Category option to show the available generators by category. Either one or any number of combinations of the categories can be chosen. For generator MW control, there are two categories available: By Area and By Zone. An area number needs to be given for By Area and a zone number for By Zone. The By Category option is temporarily disabled.

Default Settings

Weight This option sets the weighting factors for the selected generator MW controls. You need to set the weighting factor first before you click on the Select button to activate a generator MW control. This number determines the weight between different generator MW controls, with 100% being the maximum and the highest weight.



22.2.6 Shunt Comp Page This page is provided to choose the shunt compensation controls and set their associated parameters.

Active Controls This box lists information on all the selected shunt compensation controls, including the device ID, Mvar range, initial Mvar, and weighting factor. Only the selected shunt compensation devices are treated as active controls in the optimization process.

Select Button First highlight a shunt compensation device from the box underneath the button, and then click on this button to move the highlighted shunt compensation device into the Active Controls box. This box initially lists all the shunt compensation devices in the system for the specified Select Option.

Deselect Button Highlighting a shunt compensation device in the Active Controls box and clicking on this button will move that shunt compensation device into the box underneath the button to become an inactive control.



Selection Option Specify a category to show all the available shunt compensation devices in that category.

All Select this option to show all the available shunt compensation devices in the system. By Category Select this option to show the available shunt compensation devices by category. Either one or any number of combinations of the categories can be chosen. For shunt compensation control, there are two categories available: By Area and By Zone. An area number needs to be given for By Area and a zone number for By Zone. This option is temporarily disabled.

Default Settings

Min Mvar This option sets the minimum Mvar limit for the selected shunt compensation controls. You need to set Min Mvar before you click on the Select button to activate a shunt compensation control.

Max Mvar The same as Min Mvar, but the Max Mvar option sets the maximum Mvar limit for the selected shunt compensation controls.

Initial Mvar The same as Min Mvar and Max Mvar, but the Initial Mvar option sets the initial Mvar for the selected shunt compensation controls.

Weight This sets the weighting factors for the selected shunt compensation controls. You need to set the weighting factor first before you click on the Select button to activate a shunt compensation control. This number determines the weight between different shunt compensation controls, with 100% being the maximum and the highest weight.



22.2.7 Bus Voltage Constraint Page This page is provided for you to set the bus voltage constraints and their associated parameters.

Enforced Constraints This box lists information on all the enforced bus voltage constraints for load buses, including the bus ID, bus kV rating, range of variation and weighting factor. Only the selected buses are constrained in the optimization process.

Select Button First highlight a bus from the box underneath the button, and then click on this button to move the highlighted bus load into the Enforced Constraints box. This box initially lists all the load buses in the system for the specified Select Option.



Deselect Button Highlighting a bus in the Enforced Constraints box and clicking on this button will move that bus into the box underneath the button to become an unconstrained bus.

Selection Option Specify a category to show all the load buses in that category.

All Select this option to show all the load buses in the system.

By Category Select this option to show all load buses by category. Either one or any number of combinations of the categories can be chosen. For bus voltage constraints, there are three categories available: By Area, By Zone and By kV. An area number needs to be given for By Area, a zone number for By Zone, and a kV rating for By kV. This option is temporarily disabled.

Default Settings

Max. V This option sets the maximum voltage limit in percent of bus nominal voltage for the selected bus voltages. You need to set Max. V first before you click on the Select button to enforce that bus voltage constraint.

Min. V The same as Max. V, but this option sets the minimum voltage limit in percent of bus nominal voltage for the selected bus voltages.

Weight This option sets the weighting factors for the selected bus voltage constraints. You need to set the weighting factor first before you click on the Select button to enforce a bus voltage constraint. This number determines the weight between different bus voltage constraints, with 100% being the maximum and the highest weight.



22.2.8 Branch Flow Constraint Page This page is provided for you to set the branch (line) flow constraints and their associated parameters.

Enforced Constraints This box lists information on all the enforced branch flow constraints for load buses, including the branch ID, branch type, constraint type, base rating, maximum and minimum allowable branch flow, and weighting factor. Only the selected branches are constrained in the optimization process.

Select Button First highlight a branch from the box underneath the button, and then click on this button to move the highlighted branch into the Enforced Constraints box. This box initially lists all the branches in the system for the specified Select Option.

Deselect Button Highlighting a branch in the Enforced Constraints box and clicking on this button will move that branch into the box underneath the button to become an unconstrained branch.



Selection Option Specify a category to show all branches in that category.

All Select this option to show all the branches in the system. By Type Select this option to show branches by category. Either one or any number of combinations of the categories can be chosen. For bus branch flow constraints, there are three categories available: Xfmr, Cable, and Reactor.

Default Settings Button Click on this button to bring up the Branch Flow Constraint Editor.

From this box you can set and edit constraint parameters for different types of branches. All the parameters need to be set before clicking on the Select button to enforce constraints for any branches.

Constraint Choose a type of branch flow to constrain. There are four types of branch constraints available: MW, Mvar, MVA, and Amp.

Max. Maximum branch flow limit in percent of the base of branch rating for the given branch type and constraint type.

Min. Minimum branch flow limit in percent of the base of branch rating for the given branch type and constraint type.


Optimal Power Flow Display Options

22.3 Display Options The Optimal Power Flow Display Options consist of a Results page and three pages for AC, AC-DC, and DC info annotations. Note that the colors and displayed annotations selected for each study are specific to that study.

22.3.1 Results Page This page controls the result annotations of the OPF which are displayed on the one-line diagram.

Color Select the color for the optimal power flow result annotations to be displayed in on the one-line diagram.



Voltage

Voltage From the dropdown list, select either % (percent of bus nominal kV) or kV.

Bus Click on this check box to display bus voltages.

Power Flows

kVA or MVA Select kVA or MVA from the dropdown list.

KW + jkvar, kVA, and Amp Select the kW + jkvar, kVA, or Amp option to display the corresponding power flows.

%PF Check this box to display branch flow units.

Meters Select from the check boxes in this section to display readings for the corresponding meters. Meter readings available for display are: • Ammeter • Voltmeter • Multi-Meter

Show Units Check this box to show units for all flow displays.

Required Setting Select options in this section to display the required control changes/updates. Controls whose required settings can be displayed are: • Generator V • Generator Mvar • LTC • Shunt Compensation

Show Final Results Click on this option to display the final value of the control variables.

Show Requested Changes Click on this option to display the delta changes of the control variables. This option is temporarily disabled.



Elements Click on any or all of the check boxes in this section to display annotation information. 22.3.2 AC Page This page includes options for displaying info annotations for AC elements.

Color Select the color for information annotations to be displayed on the one-line diagram.

ID Select the check boxes under this heading to display the ID of the selected AC elements on the one-line diagram.

Rating Select the check boxes under this heading to display the ratings of the selected AC elements on the one-line diagram.

Device Type Rating Gen. (Generator) kW / MW Power Grid (Utility) MVAsc Motor HP / kW Load kVA / MVA Panel Connection Type (# of Phases - # of Wires) Transformer kVA / MVA Branch, Impedance Base MVA Branch, Reactor Continuous Amps Cable / Line # of Cables - # of Conductor / Cable - Size Bus kA Bracing Node Bus Bracing (kA) CB Rated Interrupting (kA) Fuse Interrupting (ka) Relay 50/51 for Overcurrent Relays PT & CT Transformer Rated Turn Ratio

kV Select the check boxes under this heading to display the rated or nominal voltages of the selected elements on the one-line diagram. For cables/lines, the kV check box is replaced by the button. Click on this button to display the cable/line conductor type on the one-line diagram.



A Select the check boxes under this heading to display the ampere ratings (continuous or full-load ampere) of the selected elements on the one-line diagram. For cables/lines, the Amp check box is replaced by the button. Click on this button to display the cable/line length on the one-line diagram.

Z Select the check boxes under this heading to display the impedance values of the selected elements on the one-line diagram.

Device Type Impedance Generator Subtransient reactance Xd” Power Grid (Utility) Positive Sequence Impedance in % of 100 MVA (R + j X) Motor % LRC Transformer Positive Sequence Impedance (R + j X per unit length) Branch, Impedance Impedance in ohms or % Branch, Reactor Impedance in ohms Cable / Line Positive Sequence Impedance (R + j X in ohms or per unit length)

D-Y Select the check boxes under this heading to display the connection types of the selected elements on the one-line diagram. For transformers, the operating tap setting for primary, secondary, and tertiary windings are also displayed. The operating tap setting consists of the fixed taps plus the tap position of the LTC.

Composite Motor Click on this check box to display the AC composite motor IDs on the one-line diagram, then select the color in which the IDs will be displayed.

Use Default Options Click on this check box to use PowerStation’s default display options.

22.3.3 AC-DC Page This page includes options for displaying info annotations for AC-DC elements and composite networks.


ID Select the check boxes under this heading to display the IDs of the selected AC-DC elements on the one-line diagram.

Rating Select the check boxes under this heading to display the ratings of the selected AC-DC elements on the one-line diagram.



Device Type Rating Charger AC kVA & DC kW (or MVA / MW) Inverter DC kW & AC kVA (or MW / MVA) UPS KVA VFD HP / kW

kV Click on the check boxes under this heading to display the rated or nominal voltages of the selected elements on the one-line diagram. A Click on the check boxes under this heading to display the ampere ratings of the selected elements on the one-line diagram.

Device Type Amp Charger AC FLA & DC FLA Inverter DC FLA & AC FLA UPS Input, output, & DC FLA

Composite Network Click on this check box to display the composite network IDs on the one-line diagram, then select the color in which the IDs will be displayed.


22.3.4 DC Page This page includes options for displaying info annotations for DC elements.


ID Select the check boxes under this heading to display the IDs of the selected DC elements on the one-line diagram.

Rating Select the check boxes under this heading to display the ratings of the selected DC elements on the one-line diagram.

Device Type Rating Battery Ampere Hour Motor HP / kW Load kW / MW Elementary Diagram kW / MW Converter kW / MW Cable # of Cables - # of Conductor / Cable – Size



kV Select the check boxes under this heading to display the rated or nominal voltages of the selected elements on the one-line diagram. For cables, the kV check box is replaced by the button. Click on this button to display the conductor type on the one-line diagram. A Select the check boxes under this heading to display the ampere ratings of the selected elements on the one-line diagram. For cables, the Amp check box is replaced by the button. Click on this button to display the cable length (one way) on the one-line diagram.

Z Select the check boxes under this heading to display the impedance values of the cables and impedance branches on the one-line diagram.

Composite Motor Click on this check box to display the DC composite motor IDs on the one-line diagram, then select the color in which the IDs will be displayed.



Optimal Power Flow Calculation Methods

22.4 Calculation Methods In traditional load flow studies, the final settings of many system control parameters are based on the engineer’s experience and judgment. Sometimes an iterative process is required to reach the final overall satisfactory settings, which can be very exhaustive for large systems. These system control parameters are typically transformer LTC settings, generator AVR settings or reactive power generations, series and shunt static var compensation device settings, the amount of load shed, and some others. In practice, any of those control settings or any combination of them can be used in a particular system. The Optimal Power Flow Study can be understood as an intelligent load flow. It employs an optimization technique to automatically adjust the power system control settings while it solves the load flow equation at the same time. Moreover, it allows you to specify a wide range of optimization criteria for your system and enforce limits on system quantities (bus voltage, line flow, etc.) during the optimization process. These optimization criteria are called objectives, usually the system performance indexes, and the limits are called constraints. Mathematically, the optimal power flow study can be expressed as: Min = f(x,u) (1) subject to the equality constraints: ΣP(x,u) = 0 (2) ΣQ(x,u) = 0 (3) and the inequality constraints: umin ≤ u≤ umax (4) y(x,u)min≤ y(x,u) ≤ y(x,u)max (5) where

x = Bus voltage vector, called state variable set u = System control vector, called control variable set f = Objective functions, expressed in terms of x and u y = System output vector, a variable set typically including line flows, etc., as a function of x and u P = Real power, expressed in terms of x and u Q = Reactive power, expressed in terms of x and u Equation (1) indicates the specified objective function to be minimized or optimized. Equations (2) and (3) show the system power balance equation (load flow equation) to be solved. Equation (4) specifies the control upper and lower limits, and equation (5) sets the upper and lower limits for output variables. The PowerStation Optimal Power Flow Analysis uses the state-of-the-art interior point optimization technique with the logarithm barrier function and the prime-dual direction searching method. The algorithm is very efficient and robust, suitable for large size systems with both equality and inequality constraints. On the power system modeling side, a true AC model is used, which makes it possible for this program to achieve the ultimate accuracy and capability in solving power system optimal power flow problems of any size under any feasible conditions.


Optimal Power Flow Required Data

22.5 Required Data The Optimal Power Flow Study essentially requires all the data needed for a regular load flow study, plus a few additional data specific for the optimal power flow calculation, and all the settings in the Optimal Power Flow Study Case Editor. A summary of the required data for different types of components for OPF calculations is given in this section.

Bus Data • Bus ID • Nominal kV • Load Diversity Factor (Loading Option is Set to Max or Min Diversity Factor) • Area Number & Zone Number

Branch Data

2-Winding & 3-Winding Transformers • Transformer ID • Rated kV & MVA • Positive Sequence Impedance, Impedance Variation, & Tolerance • X/R Ratio • Tap Settings • LTC Settings, if the Transformer LTC is Used as a Control • Max MVA, if the Transformer Flow is Constrained

Cable/Transmission Line • Cable or Transmission Line ID • Type, Size, Rated kV, # of Conductors per Phase, & Length • Use Library Data or Enter Cable Resistance, Reactance, and Susceptance Values for Positive Sequence • Allowable Ampacity, if the Cable/Transmission Line Flow is Constrained

Impedance • Impedance ID • Resistance, Reactance, & Susceptance Values for Positive Sequence

Current-Limiting Reactor • Current-Limiting Reactor ID • Rated Current & kV • X/R Ratio & Impedance for Positive Sequences & Tolerance • Amp Rating, if the Reactor Flow is Constrained

Power Grid (Utility) Data • Power Grid (Utility) ID • Operating Mode (Swing, Voltage Control, or Mvar Control) • Nominal kV • MW Loading, & Mvar Limits (Qmax & Qmin) for Voltage Control Mode • MW & Mvar Loading for Mvar Control Mode • Energy Cost Data (Min MW, Max MW, MW and $Cost Points)



Synchronous Generator Data • Synchronous Generator ID • Operating Mode (Swing, Voltage Control, or Mvar Control) • Rated kV • %V, MW Loading, & Mvar Limits (Qmax & Qmin) for Voltage Control Mode • MW & Mvar Loading for Mvar Control Mode • Fuel Cost Data (Min MW, Max MW, Model Type, MW and $Cost Points)

Synchronous Motor Data • Synchronous Motor ID • Quantity • Rated kW/hp & kV • Power Factors & Efficiencies at 100%, 75%, & 50% Loadings • Loading Category ID & % Loading • Equipment Cable Data

Induction Machine Data • Induction Machine (Motor or Generator) ID • Quantity • Rated kW/hp & kV • Power Factors & Efficiencies at 100%, 75%, & 50% Loadings • Loading Category ID & % Loading • Equipment Cable Data

Load & Shunt Device Data • Other load and shunt devices include static load, lumped load, capacitor, MOV, charger/converter, &

UPS • Device ID • Rated kVA/MVA & kV • Power Factor • Loading Category ID & % Loading

Harmonic Filter Data • Device ID • Filter Type • Rated kV & 3-Phase kvar for Capacitors • Xl & Q for Reactors • R, if Applicable • Phase Connection



Study Case Parameters • Study Case ID • Barrier Factor • Power Mismatch • Max. Iteration • Objective Precision • Loading Category • Loading Condition (if Operating P & Q is selected) • Load Diversity Factor Option & Associated Parameters • Charger Loading Option • Initial Voltage Option • Infeasibility Handling Option • Objectives & Weight Factors; Exponents, if Applicable • LTC Controls & Associated Parameters • Generator AVR Controls & Associated Parameters • Generator MW Controls & Associated Parameters • Shunt Compensation Controls & Associated Parameters • Bus Voltage Constraints & Associated Parameters • Branch Flow Constraints & Associated Parameters


Optimal Power Flow Output Reports

22.6 Output Reports The OPF calculation results are reported both on the one-line diagram and in the text format. You can use the Optimal Power Flow Report Manager (from the Study Toolbar) or View Output Report button (from the Study Case Toolbar) to view the output reports.

22.6.1 Optimal Power Flow Report Manager Click on the Report Manager button on the Study Toolbar to open the Optimal Power Flow Report Manager. The Optimal Power Flow Report Manager provides different formats for both text and Crystal Reports. Currently, only the TextRept format is available. The editor includes four pages (Complete, Input, Result, and Summary) representing different sections of the output report. There are several fields and buttons common to every page, as described below.

Output Report Name This field displays the name of the output report you want to view.

Project File Name This field displays the name of the project file based on which report was generated, along with the directory where the project file is located.

Help Click on this button to access Help.

OK / Cancel Click on the OK button to dismiss the editor and view the selected output report. If no selection is made, it will simply dismiss the editor. Click on the Cancel button to dismiss the editor without viewing the report.

Complete Page From this page, you can select the report format that gives you the complete output report. The complete report includes input data, results, and summary reports. Currently only the TextRept in ASCII format is available.



Input Page This page allows you to select different formats for viewing input data, grouped according to type. Crystal Report Formats for various input reports will be available in the future version of PowerStation.

Result Page This page provides the formats for different calculation results. Crystal Report Formats for various output reports will be available in the future version of PowerStation.

Summary Page This page provides the formats for different summary reports. Crystal Report Formats for various summary reports will be available in the future version of PowerStation.

22.6.2 View Output Reports From Study Case Toolbar This is a shortcut for the Report Manger. When you click on the View Output Report button, PowerStation automatically opens the output report, which is listed in the Study Case Toolbar with the selected format. In the picture shown below, the output report name is Untitled and the selected format is TextRept.

22.6.3 Optimal Power Flow Text Report PowerStation text output reports can be viewed by any word processor such as Notepad, WordPad, and Microsoft Word. Currently, by default, the output reports are viewed by Notepad. You can change the default viewer in the ETAPS.INI file to the viewer of your choice. The output reports are 132 characters wide with 66 lines per page. For the correct formatting and pagination of output reports, you MUST modify the default settings of your word processor application. For Notepad, WordPad, and Microsoft Word applications, we have recommend settings that are explained in the Printing & Plotting Chapter. By clicking on the View Output Report button on the Study Case Toolbar or selecting the TextRept format from the Optimal Power Flow Report Manager, you will be able to open and view the text output report for the optimal power flow study. The optimal power flow study text report contains the following major data sections:



Bus Input Data This section reports the input data related to system buses, including bus number, bus ID, bus nominal kV, area number, zone number, and the total number of buses in the system.

Bus # Bus ID kV Gen P Gen Q Mtr P Mtr Q Stc P Stc Q Area Zone

----- ------------- ------ ------- ------- ------- ------- ------- ------- ---- ----

1 Bus1 13.80 0.000 0.000 0.000 0.000 0.000 0.000 1 1

2 Bus2 2.40 20.000 0.000 0.000 0.000 0.000 0.000 1 1

3 Bus3 2.40 0.000 0.000 0.000 0.000 0.000 0.000 1 1

4 Bus4 2.40 0.000 0.000 20.400 12.643 5.100 3.161 1 1

4 buses read in.

Generator Input Data This section reports the input data related to the generators in the system, including generator number, MW and Mvar, upper and lower limits for real power and reactive power generation, and the total number of the generators in the system. Note that the power grid (utility) is also counted as a generator.

Gen # Conn. Bus MW Mvar Pmax Pmin Qmax Qmin

----- ------------- ------- ------- ------- ------- ------- -------

1 Bus2 20.00 0.00 20.00 20.00 15.00 -15.00

2 Bus1 0.00 0.00 99999.00 -99999.00 0.00 0.00

2 generators read in.

Line Input Data This section reports the input data related to all branches (lines) in the system, including line number, From and To bus IDs, R, X and Y values of the line in pu, and the total number of lines.

Line# From Bus ID To Bus ID R X Y

----- ----------- ------------- ------- ------- -------

1 Bus2 Bus4 0.0645 0.1053 0.0000

2 Bus3 Bus4 0.1291 0.2106 0.0000

3 Bus1 Bus2 0.0901 1.3971 0.0000

4 Bus1 Bus3 0.0901 1.3971 0.0000

4 branches read in.

Transformer Tap & LTC Input Data This section reports the input data related to system LTCs, including tap number, From and To bus IDs of the associated transformer, initial tap setting, maximum and minimum limits of the LTC, step change of the LTC, and the total number of LTCs. Note that only LTCs which are selected as the controls are included.

Tap # From Bus ID To Bus ID Tap Max Min Step

----- ------------ ------------ ------- ------- ------- -------

1 Bus1 Bus2 0.0000 10.0000 -10.0000 0.0063

2 Bus1 Bus3 0.0000 10.0000 -10.0000 0.0063

2 transformers read in.



Other Control Variable Input Data If there are other control variables selected in the Optimal Power Flow Study Case Editor, such as generator fuel cost, load shed, shunt compensation and series compensation, then they will also be reported in the corresponding sections.

Branch Flow Constraint Input Data This section reports the input data related to the branch flow constraints, including the From and To bus number and ID of the branch, area number, maximum and minimum flows allowed, and the flow type.

From Bus ID Area To Bus ID Area Flow(min) Flow(max) Type

----- ----------- ---- ----- ----------- ---- --------- --------- -----

2 Bus2 1 4 Bus4 1 0.000 6000.000 Amps

1 Bus1 1 3 Bus3 1 0.000 6.000 MVA

Input Variable Summary This section summarizes the total variables defined for the given system in the current study. Classification of the variables is purely from the optimization point of view. They include the total number of voltage angles, voltage magnitudes, transformer LTCs, generator MW and Mvar, and constrained branch flows.

Optimization Summary

Free Variables:

--------------------

Angles : 3

Voltages : 3

Transformers : 2

MW variables: 1

Mvar gener. : 2

Branch Flows: 2

Total optim.: 13

Objective Output This section reports the final computed objectives after the optimization solution is reached.

Minimum R loss objective: 0.004732

Minimum X loss objective: 0.012301

Bus Voltage Output This section reports the bus voltage output with both magnitude in percent of its nominal value and phase angle in degree.

Bus# Bus ID Vmag Vang

---- ------------ -------- --------

1 Bus1 100.0000 0.0000

2 Bus2 101.7727 -1.7707

3 Bus3 100.4670 -2.5219

4 Bus4 99.1109 -2.6503



Generator MW & Mvar Output This section reports the generator MW and Mvar generation as a result of the optimization.

Gen # Conn. Bus Vmag MW Mvar

----- ------------- -------- -------- --------

1 Bus2 100.0000 20.0000 13.2644

2 Bus1 101.7727 5.8830 3.7132

Branch Flow Output This section reports the final branch flows in Mw and Mvar. Flows from both ends of a branch are reported.

Line# From Bus ID To Bus ID MW Mvar

----- ------------ ------------- ------- -------

1 Bus2 Bus4 22.1980 12.2343

1 Bus4 Bus2 -21.7978 -11.5810

2 Bus3 Bus4 3.6519 4.2317

2 Bus4 Bus3 -3.6119 -4.1665

3 Bus1 Bus2 2.2031 -0.9500

3 Bus2 Bus1 -2.1980 1.0295

4 Bus1 Bus3 3.6798 4.6642

4 Bus3 Bus1 -3.6519 -4.2317

Transformer Tap & LTC Setting Output This section reports the optimized transformer tap and LTC settings. Settings are in percent, including both off-nominal tap and LTC tap.

Tap# From Bus ID To Bus ID Tap

---- ------------ ------------ ------

1 Bus1 Bus2 -0.6024

2 Bus1 Bus3 -6.3495

System Summary This section summarizes the total system loading, generation, and losses.

Total System Power Balance:

---------------------------

Active Reactive

------ --------

Fixed Load: 2.040E+01 1.264E+01

Shunt Devices: 5.010E+00 -3.105E+00

Line Charging: 0.000E+00

Generation: 2.588E+01 1.698E+01

Power Losses: 4.732E-01 1.230E+00

Largest mismatch:-9.261E-05 8.757E-04 1 Bus1


Optimal Power Flow One-Line Diagram Displayed Results

22.7 One-Line Diagram Displayed Results The one-line diagram display shows study results after the current calculation is completed. Different results can be chosen and displayed by setting appropriate options in the Optimal Power Flow Display Option Editor. A sample one-line diagram display for an optimal power flow study is shown here.


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