PowerWorld Simulator version 11. Manual

Injection Groups

Injection Group Display

The Injection Group Records Display presents data describing each injection group in the case. It is a class of Case

Information Display and therefore can be used in a manner consistent with all other case inf ormation displays. It has

a local menu from which you can print, copy, and modify its records as well as view the Injection Group Dialog. You

can also sort the injection group records by clicking on the heading of the field by which you want to sort.

To show the Injection Group Records Display, select Case Information > Injection Groups

By default, the Injection Group Records display contains the following fields:

Name

The name of the injection group. To change the name of an injection group, simply type a new name in the

corresponding cell.

Number of Gens

Identifies the number of generators contained in the injection group.

% Gen PF

Indicates the degree to which generators will contribute to the output of the injection group relative to loads. An

injection group that has a % Gen PF value of 100.0% receives all of its output from generator points; an injection

group that has a % Gen PF of 50% and a % Load PF of 50% receives equal contributions from its constituent loads

and generators.

Number of Loads

Identifies the number of loads contained in the injection group.

% Load PF

Indicates the degree to which loads will contribute to the output of the injection group relative to generators. An

injection group that has a % Load PF value of 100.0% receives all of its output from load points; an injection group

that has a % Load PF of 50% and a % Gen PF of 50% receives equal contributions from its constituent loads and

generators.

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Injection Group Dialog

The Injection Group Dialog provides information about injection groups and allows you to modify them. Specifically,

the Injection Group Dialog lists the number of generators and loads contained in the group and the percentage

contribution of generators and loads to the injection group’s output. The Injection Group Dialog also houses the

Participation Points Records display, from which you can add and delete points from the injection group’s list of

participants and change various attributes of the points.

To view the Injection Group Dialog for a particular injection group, open the Injection Group Records display by

selecting Case Information > Injection Groups from the main menu. Find the injection group in which you are

interested, and right-click it. Then select Show Dialog from the resulting local menu.

The Injection Group Dialog contains the following fields and controls:

Name

Identifies the injection group whose information is currently displayed. You can select a different name from this

dropdown box to display information for another injection group.

New, Delete

To insert a new injection group from this dialog, press New , and supply the name you want to give the new injection

group. To delete the injection group that is currently being shown, click Delete .

# Gens

Displays the number of generators contained in the injection group.

# Loads

Displays the number of loads contained in the injection group.

% Gen Part., % Load Part.

Displays the relative contributions of generators and loads to the output of the injection group.

Participation Points

The tab on the right hand side of the Injection Group Dialog lists the points that make up the injection group. This

display is called the Participation Point Record Display. By right-clicking on this display, you can add and delete points

from the injection group, and you can change the properties of specific points.

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Injection Groups

Injection Group Contributions By Area

This dialog is only available from the PV Curve tool in Simulator. Once you have defined the injection groups

necessary for your source and sink, you can click on the Areas button to display a list of the percent contribution by

area, according to the participation factors of the generators selected within each area.

Injection groups may include generator and load points from an arbitrary number of control areas. By default, the

contribution of each generator or load point is controlled just by the point’s participation factor. Sometimes you may

need more precise control over how much each generator or load contributes to an injection group’s export in order to

achieve a certain percentage contribution from each area represented in the group. For example, suppose the

injection group consists of points (generators and loads) contained in areas A, B, and C. Using the Injection Group

Contributions By Area Dialog, you can scale the factors for each of these points such that, for example, 40% of the

total contribution comes from points in area A, 30% from points in area B, and 30% from points in area C. Within each

area, the points contribute in proportion to the original participation factors you defined. However, the total contribution

from each area is determined by the percentages you enter on the Injection Group Contributions By Area Dialog.

The dialog houses a table containing the following fields:

Area Number The number of the area

Area Name The name of the area

% Contribution

The current percent contribution of the area. This is calculated as the sum of the

participation factors of the injection group’s points that belong to the area divided by the sum of all the injection

group’s points’ participation factors.

New % Contribution

The new percent contribution you want to achieve from the area. The participation

factors of the points that belong to the area will be scaled so that the area’s total participation becomes this

percentage of the injection group’s total participation.

To set the contribution for a specific area, simply type in a new value for the New % Contribution field for that area.

This is the only field you can change in the table. Only areas that are represented in the injection group by load or

generator points will be listed in the table.

After you have set the new percent contributions to your liking, click the Change Contributions By Area button. If

you changed your mind and do not want to rescale the participation factors, click Cancel.

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Import PTI Subsystems Dialog

Injection groups can be created from PTI subsystem definition files from the Injection Groups Case Information

Display. Click the right mouse button on this display and select Load > Subsystem from *.sub file from the resulting

local menu. From the Import Injection Groups Dialog, select the file name for the file to import.

If there is no ambiguity in the import file, new injection groups will be created with the defined subsystem names

without further prompts to the user. No ambiguity means that either participation points are defined for buses that

have either load or generation but not both or that no participation points are defined and that injection group

participation points will be defined based on the maximum generation for each on-line generator in the defined

subsystem. If participation points are defined without ambiguity, each participation point will be assigned to either the

load or generation at the bus split equally across all loads or generators at the bus.

If there is ambiguity in defined participation points, the Insert PTI Subsystems into Injection Groups Dialog will be

displayed. This dialog prompts the user how participation points should be handled for buses with both load and

generation or buses with no load or generation.

Buses w ith Load and Generation

This option allows the user to select how a defined participation point will be assigned if the participation point bus

has both load and generation.

Assign Participation Point to Generation

The participation point will be assigned to generation at the bus. The participation point will be split equally

across all generators, either on-line or off-line, at the bus.

Assign Participation Point to Load

The participation point will be assigned to load at the bus. The participation point will be split equally across all

loads, either connected or not, at the bus.

Buses with No Load or Generation

This option allows the user to select how a defined participation point will be assigned if the participation point bus

has no load or generation.

Ignore Participation Point

The participation point will be ignored.

Add Equivalent Load (closed load with ID=’99’ and 0 MW and 0 Mvar) and Assign Participation Point to this

Load

This option adds a connected load at the participation point bus with ID=’99’ and 0 MW and 0 Mvar. The

participation point is then assigned to this new load.

For each subsystem that is read that is found to hav e ambiguity in the defined participation points, the Insert PTI

Subsystems into Injection Groups Dialog will be displayed unless the user selects Same Options for All Subsystems

(Do not prompt again).

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Injection Groups

Participation Groups

Participation Points Overview

A participation point is a member of an injection group. It is a generator or load that participates in, or contributes to,

the output of an injection group. Each participation point record identifies the generator or load that fills this role, its

participation factor, and how that participation factor is calculated. A participation point’s participation factor identifies

the degree to which the point will contribute to its injection group’s output relative to the other points making up the

group. Participation factors may be defined as having a fixed value, or they may be re-calculated with every use to

stay true to how they were originally defined. For generators, participation factors may be defined as having a fixed

value or being equal to the generator’s MW reserve in the direction of increasing output (MAX GEN INC), MW reserve

in the direction of decreasing output (MAX GEN DEC), or their maximum output (MAX GEN MW).

Participation points are added to or deleted from an injection group using the Injection Group Dialog. The Injection

Group Dialog houses the Participation Point Records display, which allows you to add or delete points or to find out

more information about them using the Participation Point Dialog.

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Participation Point Records Display

The Participation Point Records display shows information about the points that comprise a particular injection group.

You can access this display for a particular injection group only from the Injection Group Dialog.

The Participation Point Records display is a class of Case Information Display and therefore can be used in a manner

consistent with all other case information displays. It has a local menu from which you can print, copy, and modify its

records as well as view the Generator Dialog or Load Dialog for a particular point. It also allows you to add

participation points to the group through the Add Participation Points Dialog, and to delete participation points. You

can also sort the participation point records by clicking on the heading of the field by which you want to sort.

The Participation Point Records display shows the following fields by default:

Point Type

Every participation point is either a generator (GEN) or load (LOAD).

Number

Identifies the number of the bus to which the generator or load is connected.

Name

Identifies the name of the base to which the generator or load is connected.

Identifies the ID of the generator or load.

AutoCalc?

If the value of AutoCalc is YES, the participation factor of the point is re-calculated with every use to be consistent

with the way the point’s participation factor was initially defined. If the value of AutoCalc is NO, the participation

factor is assumed fixed at its present value.

Initial Value

Indicates how the participation factor of the point was originally computed. For generators, the possible values of

this field are

SPECIFIED

The participation factor was specified as a constant.

MAX GEN INC

The participation factor was defined as the difference between the generator’s

maximum MW output and its present MW output.

MAX GEN DEC

The participation factor was defined as the difference between the generator’s

present MW output and its minimum MW output.

MAX GEN MW

The participation factor was defined as the maximum MW output of the

generator.

For loads, the Initial Value property can assume only two possible values:

SPECIFIED

The participation factor was specified as a constant.

LOAD MW

The participation factor was defined as the size of the load in MW.

The Initial Value field is important if you intend to save the injection groups to an auxiliary file and use them with

another case that might have a different generation dispatch or load profile. If you specify the Initial Value for a

point as GEN MAX INC, for example, and load the point from an auxiliary file into another case, Simulator will re-

calculate the point’s participation factor to match the generator’s positive MW reserve in that case.

The Initial Value field is also important if the AutoCalc field is set to YES, because AutoCalc uses the rule defined

by the Initial Value field to recalculate the participation factor with every use. For example, if Initial Value is MAX

GEN INC and AutoCalc is YES, the point’s participation factor will be updated to match the generator’s MW reserve

every time the point is accessed.

When you toggle the value of the Initial Value field, the point’s participation factor, shown in field ParFac, will update

to match the new definition. The Initial Value field must equal SPECIFIED for you want to change the value of the

point’s ParFac field by typing the new value directly into the field.

If AutoCalc is NO and you do not intend to use the injection group with any other case, then you should either

ignore this field or set its value to SPECIFIED.

ParFac

Indicates the participation factor of the participation point. The participation factor defines the relative contribution of

the point to the total output of the injection group. The load or generation change for each point is calculated based

on the value of the participation factor, with values for points having the largest participation factors experiencing

the greatest change.

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Add Participation Points Dialog

The Add Participation Points Dialog enables you to add participation points to an injection group. You can access this

dialog from the Participation Point Records display on the Injection Groups dialog by right-clicking in the participation

points list and selecting Insert from the resulting local menu. You can also open the Add Participation Points Dialog

by opening the Injection Groups display from the Case Information Menu, selecting an injection group in the Injection

Groups tab, and then right-clicking in the table labeled Participation Points in the Selected Injection Group and

choosing Insert from the local menu.

The Add Participation Points Dialog features three tabs, one for adding generator points, another for adding load

points, and a third for adding points from groups that have already been defined.

The three tabs are almost identical and contain the following controls:

Filtering

If the Use Area/Zone Filters box is checked, the list box beneath it, which lists generators, loads or previously

defined groups depending on the tab, will list only those elements contained in areas or zones whose

area/zone/owner filter setting is YES. If this box is not checked, all generators or loads in the case will be listed.

Alternatively, a custom filter can also be defined by clicking on the Define Filter button. This will open the

Advanced Filter dialog, which allows you to customize a filter for determining the devices to list in the display.

Once the list of devices has been set, with or without filtering, you can search through the list using the advanced

search techniques in Simulator. These techniques allow you to sort the list by name or by number, and use

wildcard characters. Simply choose Name or Number, and type the name or number you are looking for in the box.

Simulator will look for and highlight the first matching device in the list. If the first device is not the one you are

looking for, use Search Next to find the next device that matches the search criteria. For a comprehensive list of all

objects matching the search criteria, press Search All.

Element List

The box that occupies the left side of each tab lists the generators, loads, or groups (depending on which tab is

active) that can be added to the injection group. You can select multiple elements from each of these lists. To

select several elements in a row, drag the mouse to highlight the elements you want to add. Alternatively, click the

first element you want to add, press and hold the shift key, and click the last element you want to add. To select

elements that are not adjacent in the list, click the first element you want to add and hold down the CTRL key while

clicking the other elements you want to add.

Once an element is selected in the Element List, it is ready to be added to the injection group.

Participation Factors

You have several options for how to define the participation factor of the points you have selected.

For generators, you can specify a value, use the generator’s present participation factor (which comes from the

case and is displayed in the Generator Records Display), calculate the participation factor as the difference

between its present output and either the unit maximum or minimum, or its maximum output capability. For loads,

you can specify a value, or you can base the participation factor on the load’s size. For groups, you can specify a

value to use for every point in the injection group, or you can use the values already defined for the injection group.

Recalculate Factors Dynamically

If this box is checked, the participation factors of the points you are adding will be automatically updated every time

the points are used. Such points will then have an AutoCalc value of YES. If this box is not checked, the

participation factors of the points you are adding will be fixed at the values defined at the time they were created.

To add the points that you have selected, click the Arrow button. The new points will be added to the list box on the

right.

The list box that occupies the right side of each tab lists the points that already comprise the injection group. To delete

specific points from the injection group, select them from this list box and click the Trash button.

To close this dialog, click OK.

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Power Flow Solution: Solution Options

MVA Convergence Tolerance

The MVA convergence tolerance serves as a yardstick for determining when the Power Flow Solution process has

reached an acceptable solution. The MVA mismatch is computed as the maximum real or reactive mismatch at any

bus in the system. Usually, this value should be around 0.1 MVA. If you are having difficulty solving a particular

case, it may be helpful to temporarily increase the MVA Convergence Tolerance to drive the solution closer to the

actual solution, and then re-solve from this solution using the smaller MVA tolerance.

Maximum Number of Iterations

This option defines the maximum number of iterations Simulator will perform during the Power Flow Solution

process in an effort to converge to a solution. If Simulator must exceed this number of iterations, it assumes that the

power flow case is not converging and will terminate the solution process. If Simulator is configured to represent

non-converging power f low cases as blackouts, the screen will turn gray and the blackout warning message will

appear.

Do Only One Iteration

If checked, then Simulator will only perform one iteration of the load flow solution process when Single Solution is

clicked, regardless of the Maximum Number of Iterations setting.

Initialize From Flat Start Values

When checked, each Power Flow Solution is started assuming that all voltage magnitudes and generator set point

voltages are unity and all angles are zero. By default, this option is not selected. Some power flow problems can

be very difficult to solve from flat start assumptions. Therefore, use this option sparingly.

Disable Power Flow Optimal Multiplier

If checked, the Newton solution process will ignore the optimal multiplier. The optimal multiplier is a mathematically

calculated value that indicates the ability of the iterative solution process to continue towards a valid solution. If the

optimal multiplier becomes too small, it signifies that the solution process has hit a point where it is changing by

extremely small amounts during each iteration. If this happens at a point where the solution is not within the

allowed tolerance for the Newton process, the Newton process will result in a failed convergence to a valid solution.

Enforce Generator MW Limits

If checked, then generator minimum and maximum MW limits are enforced for all generators whose Enforce MW

Limits field is set to true. See Generator Information Dialog for more information. Otherwise, generator MW limits

are not enforced.

Disable Automatic Generation Control (AGC)

If checked, the enforcement of the Generation Re-dispatch to account for MW interchange constraints for all areas

is disabled. By default, this option is not checked.

Include Loss Penalty Factors in ED

If checked, the economic dispatch calculation will consider losses in determining the most economic generation

dispatch. Otherwise, the generation dispatch calculation will disregard system losses.

Enforce Convex Cost Curves in ED

The economic dispatch algorithm attempts to set the output of all generators that are set to be automatically

controlled so that the system’s load, losses, and interchange are met as economically as possible. The algorithm is

guaranteed to reach a unique solution only when all generator cost curves, which model the variation of the cost of

operating a unit with its output, are convex. If this option is checked, Simulator will identify units whose operating

point is outside the convex portion of the cost curve and set them off automatic control.

Post Power Flow Solution Actions

Clicking this option will open the Post Power Flow Solution Actions dialog, where the user can specify a list of

actions to be executed at the end of every Full AC power flow solution.

Disable Checking Gen VAR Limits

If checked, the Mvar limits are ignored for all the generators in the case during a Power Flow Solution. By default,

this option is not selected.

Check Immediate ly

If checked, violations of the Mvar limits for each generator are checked before the Power Flow Solution is started.

Normally, the Power Flow Solution is started without checking the Mvar limits until after a solution has been

reached. If any of the Mv ar limits are violated after the solution is reached, the violations are corrected, and the

power flow is solved again. With this option checked, the violations are checked before the first time the power flow

is run. By default, this option is not selec ted.

Disable Switched Shunt Control

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Solving and Simulating a Case

If checked, automatic control of switched shunts is disabled in all areas. By default, this option is not selected.

Disable LTC Transformer Control

If checked, automatic control of LTC transformers is disabled in all areas. By default, this option is not checked.

Minimum Sensitivity for LTC Control

This option specifies the minimum-voltage-to-tap sensitivity for LTC transformers. All transformers having an

absolute value of voltage-to-tap sensitivity below this value are automatically disabled from automatic control. This

prevents Simulator from changing transformer taps that have little effect on their controlling voltage. The

Transformer AVR Dialog shows the voltage-to-tap sensitivity for each voltage-controlling transformer.

Disable Balancing of Parallel LTC Taps

Simulator has the capability to attempt to balance tap positions of parallel transformers, in an attempt to avoid

parallel transformers from going to opposite tap settings, inducing loop flow through the parallel transformers.

Checking this option disables the automatic balancing of parallel transformers. The only transformers that will be

balanced are those in parallel between the same terminal buses, or those in parallel between terminal buses that

are connected with zero impedance branches.

Disable Phase Shifter Transformer Control

If checked, then automatic control of phase shifting transformers is disabled in all areas. By default, this option is

not checked.

Model Phase Shifters as Discrete Controls

If checked, then phase shifters will switch tap positions discretely based on the tap step size of the phase shifting

transformer. By default, this option is not checked, which means the phase shifters will switch continuously,

independent of the tap step size.

Prevent Controller Oscillations

Sometimes, a power flow will fail to converge because certain automatic controls such as Mvar limit enforcement at

generators, transformer tap switching, and shunt switching oscillate between their control bounds. These

oscillations very often are due to modeling inaccuracies. If this option is checked, Simulator will automatically

detect such oscillating controls and fix them at their current value so that they no longer oscillate. You may find this

option helpful if you feel that the modeling of automatic controls in your system is inaccurate.

Maximum Number Controller Loop Iterations

As part of the solution process, the outer loop of the solution algorithm is a check of any necessary controller

changes due to changes in controlled values from the last iteration of the Newton-Raphson load flow solution. The

maximum number of loops through the control change algorithm can be set here. This is not the same as the

Maximum Number of Iterations, which applies to the actual Newton-Raphson inner loop algorithm, which solves that

actual power flow.

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Post Power Flow Solution Actions Dialog

The Post Power Flow Solution Actions dialog describes a list of actions that are executed at the end of every Full AC

power flow solution, which means they are not performed for DC solutions. Normally, these actions would all have

Model criteria specified.

To open this dialog, select Options > Solution Environment. Next, click the button labeled Post Power Flow

Solution Actions on the Power Flow Solution tab, Solution Options tab of the PowerWorld Simulator Options

dialog.

Check the Do Not Used Post Power Flow Solution Action List check-box to avoid using these actions.

The action list display identifies the actions that comprise the post power flow solution action list. Actions can be

inserted or deleted by using the local menu on the dialog. Right-click on the display and select Insert or Delete .

Actions are inserted via the Contingency Element Dialog.

The action display is a type of Case Information Display and thus shares many characteristics and controls common to

all other case information displays.

The Action List Display always contains the following fields:

Actions

This shows a string which describes the action. You may customize the format of the string that describes the

actions by right-clicking on the Action List Display and choosing Display Descriptions By, and then choosing

either Name, Num, Name/Num, PW File Format by Numbers, PW File Format by Name/kV or PTI File Format.

Model Criteria

Simulator allows you to define Model Criteria, which consist of both Model Conditions and Model Filters. These

specify a criteria under which a contingency action would occur. For example, you could specify that a generation

outage only occur if the pre-contingency flow on a line is higher than a specified amount. Normally, no Model

Criteria will be specified, and this field will be blank. Also, note that Model Criteria can be overridden by the Model

Condition and Filter option on the Contingency Options Tab. You can open a dialog to define Model Filters or

Conditions by right-clicking on the Action List Display and choosing Define Model Criteria.

Status

Three options are available for this field

CHECK : The action will be executed only if the Model Criteria is true. It will also be executed if no model

criteria is specified. This is the default setting

ALWAYS: The action will always be executed, regardless of the Model Criteria.

NEVER: The action will never by executed, regardless of the Model Criteria.

POSTCHECK: This action is checked AFTER the other Check and Always actions have been performed

and the load flow solution solved. If the criteria specified for the Postcheck action are met in the resulting

load flow solution, then this action is taken and the load flow is again resolved. This will recursively occur

for all Postcheck actions until either all postcheck actions have been taken, or the criteria for all remaining

postcheck actions have not been met.

Note that the Never action allows you to disable a particular action without deleting it.

Comment

A user-specified comment string that can be associated with this action. While this comment is not used by

Simulator in any way, these comments can be saved to be loaded at a later time. This is provided for the user to

add comments regarding the action. For example, for an action with a Model Criteria you may could add a

sentence explaining why the action is only performed under the specified criteria.

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Solving and Simulating a Case

Power Flow Solution: Island-Based AGC

The Island Based AGC options allow the user to choose to dispatch generation by island instead of by area or super

area. The options available for dispatch here are:

Disable (Use the Area and Super Area Dispatch Settings)

When this option is selected, Island Based AGC is being used, and generators are dispatched according to the

usual area or super area generation dispatch.

Use Participation Factors of individual generators

When selected, the island-based AGC is used, based on the individual participation factors of each generator within

the island. Area and super area ACE requirements will be ignored, and all generators in the island will be

dispatched to serve load, losses, and any DC transfers to other islands.

Calculate Participation Factors from Area Make Up Power Values

The AGC will dispatch generation by area participation factor, instead of by individual participation factor. What this

means is that each area will be assigned a participation factor, similar to assigning a participation factor to a

generator. Based on the participation factor each area in the island, the amount of the generation dispatch needed

will be divided amongst each area based on its factor. Higher factors will account for more of the generation

dispatch than areas with smaller factors. The within each area, the generation dispatch is handled on an individual

generator participation factor basis, where each generator will account for a portion of the dispatch that was

assigned to its area.

For example, three areas have participation factors of 2, 1 and 1, respectively. If the total generation redispatch in

the island is 100 MW, then area 1 will account for 2 / (2+1+1), or 50%, of the total. Therefore area 1 is expected to

redispatch by 50 MW. If area 1 then has two generators with participation factors of 4 and 1, they will account for

the 50 MW by picking up 4 / (4+1) and 1 / (4+1), or 80% and 20%, respectively, of the 50 MW needed from the

area.

Dispatch using an Injection Group (Loads and Generators will respond)

Checking this option will allow for the island dispatch to be covered by change in generation and/or load defined in

an injection group.

Additional options are available when dispatching based on an injection group:

Allow only AGC Units to Vary

If this option is checked, only units whose AGC status is turned on will be allowed to participate in the injection

group dispatch.

Enforce unit MW limits

If checked, then each generator’s defined MW limits will be strictly adhered to during the redispatch.

Do not allow negative loads

When checked, loads included in the injection group are not allowed to drop below zero MW or MVAR load

demand.

How should reactive power load change as real power load is ramped?

You can choose to keep the ratio of real and reactive power constant for each load that is included in the

injection group, or you can specify a constant power factor that the MVAR value will be determined from when

the MW value is changed.

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Power Flow Solution: DC Options

Use DC Approximation

When this box is checked, Simulator will solve the load flow using the DC Approximation method. When not

checked, Simulator performs the modified Full Newton AC load flow algorithm. Note that once a case, especially a

large one, has been solved using a DC approximation, it tends to be quite difficult to revert back to the Full Newton

AC load flow from a solved DC approximation.

Compensate for Losses by Adjusting the Load

Traditionally a DC load flow is treated as lossless. However, you can approximate the loss in the load flow by

artificially adjusting the load in the case to include estimated losses. To do so, click on the DC Loss Setup button

to open the DC Power Flow Loss Setup dialog for setting the DC Loss Multipliers.

Compensate for Reactive Power Flows by Adjus ting the Branch Limits …

One issue with DC load flow is how to treat the inclusion of reactive power flows. In a standard DC load flow, the

reactive flows are typically ignored, and the MW flow of a branch is compared to its original MVA branch limit.

However, Simulator also gives you the option to instead solve the DC load flow and compute approximate MVAR

flows by assuming the voltages in the system remain constant when the DC load flow is solved.

Compensate for Dispatch Sensitivities with User-Specifie d Values

This option allows for the bus MW loss sensitivities to be used in the OPF and ED dispatch algorithms, if the type of

loss sensitivity on the General tab is set to User-Specified.

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Solving and Simulating a Case

DC Power Flow Loss Setup

To open the DC Power Flow Loss Setup dialog, select Options > Solution/Environment. . Next, click the button

labeled DC Loss Setup on the Power Flow Solution tab > DC Options tab of the PowerWorld Simulator Options

dialog.

The DC Power Flow Loss Setup dialog gives you a location to apply approximate losses during a DC load flow

solution. The losses can be approximated by scaling the loads in the case to include an approximation of losses.

Loss multiplication factors can be applied individually by bus, or as a group by area or by zone. Note that loss

multipliers by area or by zone are just quick ways for setting the bus multiplication factors for all buses in the group.

You will see the value reflected for all buses in the Buses page. If you wish to apply the same multiplication factor to

the entire case, you can simply set the Case DC Loss Multiplier at the bottom of the dialog. This will automatically set

all buses in the case to have the same DC Loss Multiplier specified.

Once the DC Loss Multipliers have been set, click OK to save the multipliers.

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Power Flow Solution: General

Dynamically add/remove slack buses as topology is changed (Allow Multiple Islands)

If checked, multiple islands are allowed during the solution by Simulator dynamically choosing a new slack bus for

the island. If there are no in-service generators in the new island, the island cannot be solved and will be isolated

and ignored during the load flow solution.

Restore Initial State on Restart

If checked, a paused simulation will revert to initial conditions whenever the user selects Simulation, Play from the

main menu to start a simulation, or selects Simulation, Reset followed by the Play option to restart a simulation.

Otherwise, selecting Play with a paused simulation will simply resume the paused simulation.

Assumed MVA Per-Unit Base

This option allows the user to specify the MVA base to be used for the entire case. By default, this value is set to

100 MVA.

Play/Animation Solution Method

This option is available only for OPF releases of Simulator. Use it to indicate whether Simulator’s repetitive power

flow should perform a normal power flow solution or an optimal power flow (OPF) solution.

Bus Loss Sensitivity Function

Bus loss sensitivities indicate how island or area losses change with power injection at the bus. Here you may

choose to forego the calculation of bus loss sensitivities or to base them on island losses or area losses. If the case

consists of only one island, which, by definition, corresponds to the entire system, then the bus loss sensitivities are

measured with respect to total system losses. If the bus sensitivities are set to User-Specified, the sensitivities will

remain at their last calculated values, according to the loss function type previously specified when the loss

sensitivities were calculated.

Monitor/Enforce Contingent Interface Elements

This global location allows you to determine how contingency elements in an interface should be treated in

Simulator. You can choose to never include the impact of contingent elements on interface flow, to only include

contingent element impacts in the standard power flow or optimal power flow routines, or in all solution routines

including contingency analysis and security constrained OPF.

It is not uncommon to ignore the impact of contingent elements when using the contingency analysis or security

constrained OPF tools, as they are already processing lists of contingencies and evaluating flows on interfaces.

Ignoring contingent elements within interface definitions allows for a determination of the impact of other

contingencies on the flows of the non-contingent elements forming the interface, without impact from additional

contingent element considerations.

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Solving and Simulating a Case

Power Flow Solution: Storage

Simulator offers the ability to restore either the last power flow solution state or the state of the system immediately

before the last solution attempt. If your system has insufficient memory and you are working with large systems, you

may wish to disable one or both of these options.

Disable "Restore last solution"

Restoring the last solution will undo any changes made to the data that were made after the last successful solution

and return the case to the last valid solution. For large cases, the amount of memory required to store the last

solution can be significant. If this option is checked, Simulator will not store this information in memory, and the last

solution cannot be restored if a solution fails.

Disable "Restore state before failed solution attempt"

Restoring the state before failed solution attempt will undo only the attempted solution, but will retain any changes

to data that were made before the solution process. This allows the user to return to the point just before the

solution in order to add or remove changes in an effort to obtain a valid solution. For large cases, the amount of

memory required to store the state before a solution attempt can be significant. If checked, Simulator will not store

the state information in memory, and the state before the failed solution cannot be restored.

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Solving and Simulating a Case

Environment Options

The Environment Options Tab provides you control over a number of display and simulation options. The first section

of the page contains a list of check boxes that you can use to designate the content of the oneline displays.

These options include:

Show Log

If checked, the message log is displayed. The message log shows detailed results of each Power Flow Solution.

Usually this log is NOT shown. However, if you are running into problems with a simulation case, it can prove

useful for debugging the case.

Auto Load Script File

If checked, the script file is automatically loaded with the case. This is not checked by default. Note: scripts can be

loaded manually from an option in the simulation menu.

Disable Showing Blackouts

You can dramatize a power flow case’s failure to converge by representing it as a blackout. The background of the

oneline diagram will become a dark shade of gray, and a message box will appear to announce that the system has

experienced a blackout. To disable this behavior, select the Disable Showing Blackouts box. Representing the

failure to converge as a blackout can be very helpful for presentation purposes. Very often, the power flow’s failure

to converge can be traced to the system’s inability to serve the load demand, a situation that requires that load be

"blacked out," or shed, to restore the system to a viable operating state. Thus, displaying the failure to converge as

a blackout has physical significance.

Auto Open Bus Records if No Oneline

If a case is opened in Simulator which does not have an associated oneline diagram, then Simulator will

automatically open the Bus Records case information display if this option is checked.

Disable AGC When Manually Changing Generator MW

When this option is checked, changing the MW output of a generator manually will automatically remove a

generator from Automatic Generation Control. If you wish for generators to maintain their automatic generation

control settings following a manual change of MW output, you must uncheck this option.

Automatic Archiving of PWB Files

This option allows you to effectively make backup copies of your working case every time you save the pwb file.

For example, assume you have a case named Test Case.pwb. With the Automatic Archiving turned on, saving the

case will first create a copy of the original file and rename it Test Case_1.pwb. The character used as a delimiter

can be chosen optionally. The case with any changes you have just made will then be saved as the new Test

Case.pwb file. Each time you save the case, the latest version is named Test Case.pwb, the last Test Case.pwb is

renamed with the delimiter and 1 appended, and all other archived versions will be renamed with their number

incremented by 1. The number of archive versions to maintain can also be chosen by setting the maximum number

of archive files property.

Automatically Load Contingencies when Case is Opened

If checked, Simulator will open the file specified in the Contingency File field when the case is opened and load the

contingencies from the file into memory.

Automatic Loading of Auxiliary File

A default auxiliary file can be loaded when each case is opened by checking the Automatically Load Auxiliary

File when Case is Opened check box. The auxiliary file given under Auxiliary File will then be loaded with each

case. The full path needs to be included with the file name.

Power Units for Display

Allows switching between displaying power values in Mega- units or Kilo- units.

Clock Style

The clock serves as a timer for timed simulations by showing the current time, the start time, and the end time of the

simulation. You can choose to hide the simulation clock by specifying a clock style of None. Otherwise, to display

the clock in its own window, choose Dialog, and to display the clock on the program’s status bar, select Status Bar.

Measurement System

This option allows the user to choose English (Imperial) or Metric (SI) units for system measurements. By default,

this option is set to English units.

Recently Used File List Entries

The maximum number of file names and locations stored in the History List of the File menu.

457

Oneline Options

These options are available on the Oneline tab of the PowerWorld Simulator Options dialog.

Show Oneline Hints

If checked, pop-up hints will appear when you drag the mouse over an object in the oneline. These give information

about the object; for example, for a generator the pop-up hint displays the bus number, generator ID, the MW output

and the MVAR output.

Show X,Y Coordinates

If checked, the (x,y) location of the cursor is monitored in the status bar at the bottom of the screen. The (x,y)

location of the cursor is only shown in Edit Mode. By default, this option is selected.

Save Contour Image with Oneline File

If checked, and if a contour is being displayed on the oneline diagram, Simulator will store the contour with the

oneline diagram when you save the case or save the oneline.

Display Only

If checked, Simulator only displays the case; it does not solve the power flow equations. System flows are

determined by the initial values in the case file. This option should be checked if you simply want to use Simulator

to visualize a case that has already been solved. The advantage of the display-only mode is that animation is

significantly faster, particularly for large cases. The drawback to the display-only mode is that the power flow

equations are not automatically solved at each time step; you must explicitly call for a Power Flow Solution using

either the Single Solution button of the Program Toolbar or one of the two Power Flow Solution options available

from the Simulation menu on the main menu.

Minimum Screen Font Size

The minimum font size at which text is visible on the screen. This is useful w hen zooming out on a oneline diagram

where a lot of text might become cluttered or hard to read on the screen.

Minimum Print/Copy Font Size

The minimum font size at which text can be printed or copied. This is useful if the application or printer you are

sending to can or cannot display smaller fonts.

Visualizing out-of-service elements

These three options allow you to choose how objects on the diagram should appear when they are representing a

power system device that is currently "open" or "out-of-service." The three options are Blink, Use dashed lines, and

Draw and X through off-line generators. The first two options apply to any oneline object, while the third option is

specific to generator objects only.

Transformer Symbol

Since transformer representation varies in different countries, this option allows the user to represent transformers

as coils or circles. By default, transformers are represented as coils.

Main Oneline File

This option is used to identify the primary oneline diagram to use with the case. The main oneline is the file that is

displayed when you first open the case. The dropdown box lists all the oneline files that reside in the same

directory as the case. Select one of these files, or enter the full path of the oneline you want to use if it does not

appear in the dropdown box.

Use Default Oneline File

You can command Simulator to open a particular oneline diagram file if it cannot find a oneline diagram file for the

case you are trying to open. For example, there is no oneline diagram associated with a PSS/E raw data file when

you first read it into Simulator. However, if your application is such that you will always use the same oneline file

whenever you open a PSS/E raw file, check the Use Default Oneline File to have Simulator open the oneline

identified in the Default Oneline File box whenever it encounters a case that has no associated oneline. The

default oneline must exist in the same directory as the case you are trying to open.

Save Onelines when Saving Case

By default, Simulator always saves any oneline diagrams that are open when the user chooses to save the case

(pwb) file. This option allows you to choose to be prompted to save oneline diagrams when a case file is saved, or

to never save onelines when the case file is saved.

Oneline Browsing Path

This option applies when you have Oneline Links included on a oneline diagram. Rather than specify the full path

and name of a oneline diagram as a oneline link, you can specify the file name only. When the link is clicked in Run

458

Case Information Display Options

PowerWorld uses numerous case information displays to show power system data in tabular format. The options

presented on this page of the PowerWorld Simulator Options Dialog control some of the general features of the case

information displays.

Enterable Field Color

Fields whose values can be directly entered on the case information displays are colored navy blue by default.

Click on the color field to change the color of enterable fields, or click the Change button.

Toggleable Field Color

Fields whose values can be toggled (changed) by left-clicking on them are colored green by default. Click on the

color field to change the color of toggleable fields, or click the Change button.

At or Exceeding Limit Color

Fields whose values are at or exceeding a limit, are colored red by default. Click on the color field to change the

color of such fields, or click the Change button.

Normal Field

Fields that cannot be modified directly from the case information display are colored black by default. Click on the

color field to change the color of such fields, or click the Change button.

Field not presently used

Fields whose values are overridden by other instances of the program are colored gray by default. Click on the

color field to change the color of such fields, or click the Change button.

Background

Background of cells is colored white by def ault. Click on the color field to change the color of the background, or

click the Change button.

Heading Background

Background of column and row headings is colored light gray by default. Click on the color field to change the color

of the heading background, or click the Change button.

Data Fill Background Color

Background of selected cells when propagating values is colored yellow by default. Click on the color field to

change the color of the heading background, or click the Change button.

Set Case Info Factory Default Colors

Clicking the Dark Colors button will reset the field and background colors to the defaults mentioned above, which

comprise dark colors for fields, and light colors for backgrounds. Clicking the Light Colors button will set field and

background colors to a specified set of light colors for fields and dark colors for backgrounds.

Save as Auxiliary File Data Format

This option allows the user to decide if the auxiliary files that can be saved from case information displays should be

space delimited files or comma delimited files.

View/Modify Default Font

Clicking this button brings up a font dialog from which you can choose the font in which case information displays

should show their data. Selecting a new font, font size, style, or color and pressing OK will change the default font,

so that all case information displays will then employ a font having the selected properties.

Default Row Height

This option sets the height of the rows in the case information displays. This field may need to be changed

depending on the screen size and font size of the computer. By default, the height is set to 20.

Column Headings

This option allows you to choose whether the column headings of the case information displays are the normal

column headings, or are the variable names of the type of data stored in each column.

Highlight Key and Required Field Column Headings

If this option is checked, the key fields needed for identifying objects will be highlighted in the case information

display. These fields are important if you are planning on pasting data back into Simulator from Excel, or reading

data in from an auxiliary file. If the necessary key fields are not present in the Excel paste of auxiliary file, the data

in those formats cannot be processed by Simulator.

Similarly, the Required Field Column Headings can also be highlighted in the case information display. In order for

Simulator to create new objects by reading them from an auxiliary file or and Excel paste, the required fields must

be present in the pasted data or the object cannot be created.

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Solving and Simulating a Case

Copy/Send Options

Typically when you copy information to the clipboard or send data to excel from a case information display, the first

two rows of the copied information contain the type of object the data represents (object name) and the column

headings for each column of data. These rows are necessary if you intend to paste the information back into

Simulator, but are unnecessary if you are only exporting data to another program with no intention of pasting the

information back into Simulator. Thus these two options allow you to choose which of the two rows, if either, you

wish to have copied along with the actual data from a case information display when pasting in another application.

Disable Auto Refresh

This option prevents Simulator from automatically updating the contents of open case information displays with

each solution. If this option is not checked, the data in all open case information displays will be updated

automatically to reflect the system state calculated from each Power Flow Solution.

Set Factory Defaults

Clicking on this button will reset the options to their defaults.

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Solving and Simulating a Case

Solution and Control

Simulation Control

The main function of the PowerWorld Simulator is to simulate the operation of an interconnected power system. The

simulation may focus on a single instant of time or may chart the evolution of the system over time using a series of

system snapshots. The Simulation Menu and the corresponding Program Toolbar are used to control both types of

simulation. For timed simulations, the menu is used to start/continue the simulation, pause the simulation and reset

the simulation to its starting parameters. The system clock is usually visible during a timed simulation and shows the

current simulation time along with the simulation’s start and end time. The system clock will appear either in its own

window or as a series of panels in the right corner of the window’s status bar. See Environment Options for more

information on displaying the system clock. The other type of simulation, that of a single instant of time, is

accomplished by selecting Single Solution from either the main menu or the Program Toolbar. This activity performs

a single Power Flow Solution. See Solving the Power Flow for more information.

The following tasks are available from the Simulation Control menu and the Program Toolbar:

Starting a Timed Simulation

To commence a timed simulation, select Simulation > Play from the main menu, or click the play button on the Run

Mode Toolbar. The simulation clock, visible in either its own window or the status bar, will keep track of the

simulation time. Regardless of the speed of your computer, the simulation time will change at a fixed rate that is

governed by the Simulation Speedup selected in the Simulation Options Dialog.

You can reset the simulation at any time by choosing the Simulation > Restart command, or by clicking the restart

button on the Run Mode Toolbar.

Pausing a Timed Simulation

Once the simulation has started, you can pause it at any time by selecting Simulation > Pause from the main menu

or by clicking the pause button on the Run Mode Toolbar. It is helpful to pause the simulation when you want to

take a closer look at a particular instant of the simulation.

Continuing a Timed Simulation

Once the simulation has been paused, you can continue with the simulation by selecting Simulation > Play from

the main menu, or by clicking the play button on the Run Mode Toolbar.

Restoring a Previous Solution or a Previous State

Sometimes a power flow attempt won't converge to a solution. When this occurs, the voltages and angles

calculated by the solution engine will not satisfy the real and reactive power balance constraints at each bus. Then,

the state currently stored in memory will not be an actual system operating point. It is often very difficult to coax the

system to solve once it has failed to converge.

To help you recover from a solution attempt that has failed to converge (both timed simulations and single

solutions), Simulator offers you two options.

After Simulator solves a system successfully, it will store the voltages and angles it found in memory. If the

changes that you then make to the system result in a system that can't be solved, you can select Simulation >

Restore > Last Successful Solution to reload the results of the last converged solution. After reloading this

information, Simulator will re-solve the system and refresh all displays.

In addition to restoring the last converged solution, Simulator also gives you the ability to restore the state of the

system as it was just prior to the uns uccessful solution attempt. This can be thought of as "un-doing" the effect of

the solution attempt. Before attempting a solution, Simulator stores the state of the system in memory. If it solves

the power flow successful, Simulator will discard this pre-solution state. However, it the power flow fails to

converge, Simulator will keep the state in memory. To recover it, select Simulation > Restore > State Before Last

Solution Attempt from the main menu. Simulator will replace the non-converged post-solution state with the pre-

solution state and refresh the displays. You can then play with the system to try to make it easier to solve.

If you are working with large systems, you should be aware that saving these system states can consume a lot of

memory. Therefore, Simulator offers you the option to disable one of both of these features. To do this, select

Options > Solution/Environment... to open the Solution/Environment Dialog, and then go to the Storage sub-tab

of the Solution tab. You will see two checkboxes there that can be modified to control whether or not these extra

system states are saved.

Performing a Single Solution

Whenever a timed simulation isn’t currently active, you can instruct Simulator to perform a single power flow

calculation by s electing one of the solution types from the Simulation menu. In addition, the single solution

button solves the power flow using the either the Full Newton AC load flow or the DC Approximation load flow, as

specified in the Solution / Environment Options. The simulation time and total system costs do not change as a

result of the single solution.

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Reset to Flat Start

Select Simulation > Reset to Flat Start from the main menu to initialize the Power Flow Solution to a "flat start." A

flat start sets all the voltage magnitudes and generator setpoint voltages to 1.0 per unit and all the voltage angles to

zero. Usually, a flat start should be used only if the power flow is having problems converging. You can also use

the flat start option on the Simulation and Environment Options Dialog to initialize every solution from a flat start.

Robust Solution Process

The Robust Solution Process provides a method to attempt to reach a solution when the standard load flow

(Newton-Raphson) solution fails. The robust process performs a solution in a series of steps.

First, the robust solution will turn off all controls in the case. Then the load flow will be solved using a fast

decoupled power flow. If the fast decoupled power flow reaches a solution, Simulator then immediately solves the

load flow using the Newton-Raphson load flow, still keeping the controls turned off. If the Newton-Raphson solution

is also successful, Simulator will begin adding controls back into the solution process, one type of control at a time.

Thus the generator MVAR controls are added back in, and the load flow is resolved. Then the switched shunt

controls are restored, and the load flow is again resolved. Simulator will continue in this manner by reintroducing

next the LTC control, followed by the area interchange control, and lastly the phase shifter control. Furthermore,

when reintroducing the phase shifter control, the controls are added one at a time for each phase shifter, with a load

flow solution occurring after each.

Primal LP

Choosing this menu option is the same as choosing the option LP OPF > Primal LP. Simulator will attempt to solve

an Optimal Power Flow, provided that all setup requirements for performing an OPF have been completed.

Open Script File, Clear Script File

If you wish to apply commands from a script file to Simulator, you can do so by loading a script file using the Open

Script File option. To remove a loaded Script file from memory, use the Clear Script File option.

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Solving and Simulating a Case

Solving the Power Flow

At its heart, Simulator is a Power Flow Solution engine. Power flow is a traditional power engineering calculation that

is performed to determine the flows on all lines and the voltages at all buses in the system given the power injections

at all buses and the voltage magnitudes at some of them. When Simulator performs a timed simulation, it actually

performs a sequence of power flow calculations, each based on data that present a snapshot of system conditions at a

particular instant. Since it is based on power flow, Simulator models the system as being of constant frequency. This

assumption is only an approximation, but frequency deviations are generally very small in everyday operation.

The power flow problem entails solving a system of nonlinear equations. Solving a nonlinear system requires the use

of an iterative algorithm to hone in on the correct solution. Many nonlinear system solvers have been developed, and

PowerWorld provides access to the full Newton-Raphson method.

Usually, the power flow computation converges quickly. However, it is certainly possible to model conditions for which

no Power Flow Solution exists, or for which the algorithm cannot converge to the solution within the maximum number

of iterations specified. For such situations, the message log will provide a message indicating that the computation

failed to converge. Furthermore, unless blackouts are disabled, the screen is grayed, and a message indicating a

blackout has occurred is shown.

465

Area Control

One of the most important aspects of interconnected power system operation is the requirement that each operating

area changes its total generation to match changes in the sum of its load plus losses plus power transactions with

other areas. This requirement is normally met by Automatic Generation Control (AGC). The purpose of AGC is to

ensure that the actual MW output of an area is equal to the scheduled MW output of the area. The AGC system

accomplishes this by first calculating the Area Control Error (ACE), which is defined as

ACE

Pactual - Pscheduled + (a term dependent upon system frequency)

where Pactual

is the actual amount of MW flowing out of an area. If power is flowing into the area, Pactual is negative.

Pscheduled is the amount of power scheduled to flow out of the area and thus equals the areas total sales minus its total

purchases, both expressed in MW. The last term in the ACE depends upon the deviation of the actual system

frequency from the scheduled system frequency. When the system frequency is modeled using constant frequency,

this term is always equal to zero. Otherwis e, the equation assumes uniform, but not constant, frequency throughout

the system. In this case, this term, known as the frequency bias, equals

-10 B Df, where B is an area specific bias

factor with units of MW/0.1 Hz (always negative), and Df is the deviation of the frequency from the nominal frequency

(usually either 50 Hz or 60 Hz). Simulator currently always assumes a constant frequency.

In Simulator, Pscheduled has two components, Scheduled Transactions and Base Transactions. The two types are

provided in order to simplify transaction modeling in some studies. Scheduled Transactions have a specified starting

time, ending time, MW amount, and price. However, in many power flow studies in which one is concerned only with

the static flow of power in the transmission network and not specifically with cost information, it is much easier just to

model the net flow of power from one area to another (or even to an unspecified area). For these situations, there is

no need to specify price or start and end times. Simulator refers to these as Base Transactions. Both Base and

Scheduled Transactions can be defined on the Area Information Dialog.

Whenever the ACE is greater than zero, it means that the area is over generating and thus needs either to decrease

generation or to sell more. Likewise, whenever the ACE is less than zero, the area is under generating and thus

needs either to increase generation or to buy more. AGC works to keep the ACE close to zero.

In Simulator, there are five options for implementing AGC:

No area control

The output of the generators does not change automatically. You must manually change the generation to match

system load/losses/transaction variation.

Participation Factor Control

The output of all AGC generators in the area change automatically to drive the area control error (ACE) to zero.

Each generator’s output is changed in proportion to its participation factor. Checking this option enables the Set

Factors button, which, when pressed, opens the Generator Participation Factors Dialog. Participation Factor

Control only adjusts generation when a disturbance to the system has been put in place, such as changing the

amount of load in the case, or defining new area to area transactions.

In Participation Factor Control, the ACE is allocated to each AGC generator in the area in proportion to that

generator’s participation factor divided by the total of the participation factors for all AGC generators in the area. A

generator’s participation factor cannot be negative. By default, a generator’s participation factor equals its current

MW setpoint value, but individual participation factors can be changed.

Economic Dispatch Control

The output of all AGC generators in the area changes automatically to drive the area control error (ACE) to zero.

Each generator’s output is changed so that the system is dispatched economically, based on cost information

entered for the generators in the case. Note that cost data is not generally included in standard load flow data.

Without realistic cost data entered into Simulator, the use of the economic dispatch algorithm may not be very

useful. Cost data must be obtained from another source and entered into a case in Simulator, either manually or

through the use of Simulator Auxiliary Files.

With Economic Dispatch (ED) Control, Simulator tries to change the output of the area’s AGC generators

economically so that the area’s operating cost is minimized. ED control recognizes that some generators are less

expensive than others and tries to use the least expensive generators to the largest extent possible.

To do economic dispatch, we need to know how much it would cost to generate one more MW at a particular

generator. This is known as the incremental or marginal cost. The incremental cost for each generator is modeled

using the formula:

= ICi (Pgi) = ( bi

+ 2ci Pgi

+ 3di (Pgi) 2 ) * fuelcost

$/MWH

The plot of ICi(Pgi) as a function of Pgi is know as the incremental-cost curve. The economic dispatch for a system

occurs when the incremental costs for all the generators (li) are equal. This value is known as the system l

(lambda) or system incremental cost. Its value tells you how much it would cost to generate one more MW for one

hour. The system lambda becomes important when trying to determine whether or not an area should buy or sell

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Solving and Simulating a Case

power. For example, if an area can buy power for cheaper than it can generate it, it might be a good idea for the

area to buy power.

Optimal Power Flow (OPF)

The OPF option will only be available if you have the OPF add-on for PowerWorld Simulator. The OPF control is

very similar to the Economic Dispatch control in that it attempts to dispatch generation to minimize costs. The

additional function of the OPF is to minimize the costs while also obeying line, transformer, and interface limit

constraints. This option is also not useful without realistic generator cost information, which usually must be

obtained from another source and entered into Simulator to augment a load flow case.

The OPF control also relies on the cost curve in order to perform an economically optimal power flow. However, the

OPF routine makes use of piecewise linear curves in its solution algorithm. This does not prevent you from entering

the cost information as cubic cost models, described by the equation above. Rather Simulator’s OPF routine allows

you to specify how to break up the cubic curve and model it as a piecewise linear curve for the OPF algorithm.

Area Slack Bus Control

Only the output of the area’s slack bus changes automatically to drive the area control error (ACE) to zero. This

type of generation control is usually only good for small disturbances to the injections and/or transactions in a case,

and can often fail to find a solution when larger disturbances are examined.

In addition, you can also enter piecewise linear curves directly instead of the cubic cost curve models. In fact, a

mixture of piecewise linear and cubic models is acceptable. For the economic dispatch routine, whichever type of

model is entered will be used directly for each generator. For the OPF routine, all piecewise linear curves entered

directly will be used as is, and any cubic models entered will be converted to piecewise linear curves internally during

the processing of the OPF algorithm.

467

Set Generator Participation Factors

Participation factor control is another of Simulator’s mechanisms for distributing an area’s responsibility to serve its

load, losses, and interchange. It is particularly well-suited to implementing automatic generation control (AGC) when

you do not have good economic information for an area’s generators. With participation factor control, the amount of

power that each generator contributes to meeting its areas load, loss, and interchange responsibilities is controlled by

the size of its participation factor. The unit that has the largest participation factor contributes the most, and the unit

that has the smallest participation factor contributes the least.

The Set Generator Participation Factors Dialog gives you a convenient way to define the participation factors for

multiple generators. You can set the participation factor according to a number of different formulae and then apply

this prescription to all generators in a specific area, all generators in a specific zone, all generators in the system, or all

generators whose display filters are currently set to true.

To display the Set Generator Participation Factors Dialog, you first need to open the Area Information Dialog and

switch to the Options page. The Area Information Dialog has a button labeled Set Participation Factors that is

enabled only if the Participation Factors is selected under the Area Control Options heading. Set the area on

participation factor control by selecting the Participation Factors option, and then press the Set Participation Factors

option.

The Set Generator Participation Factors Dialog is divided into two parts. The first part, which occupies the top half of

the form, allows you to indicate how the participation factors should be calculated or set for each generator. Your

options include:

Max MW Rating of Generator

The participation factor for each generator is set to the generator’s

maximum MW capability.

Difference Between Max and Current Output The participation factor for each generator is set to the generator’s

reserve power, so that each generator participates in proportion to

how much it has left to contribute.

Constant Value of

The participation factor for each generator is set to the same hard-

coded value.

File

The participation factor for each generator is read from a file. The

first line of the file should contain the keyword NUMBERS or NAMES

indicating whether generators are identified by bus number or by bus

name in the file. All subsequent lines should be comma-delimited

and contain three fields: the number or name of the generator’s bus,

the generator’s id, and the generator’s participation factor.

If you choose any of the first three options, you then must tell Simulator to what generators you want to assign the

participation factors. To assign the participation factors to all generators in a specific area, select the All Generators

in Area option, and then choose the area from the adjacent dropdown box. If you want to assign the participation

factors to all generators in a specific zone, select the All Generators in Zone option, and then choose the zone from

the adjacent dropdown box. If you want to assign the participation factor to all generators in the system regardless of

their area or zone affiliation, select the All Generators in System option. Finally, if you want to assign the

participation factor to just those generators whose display filter criteria evaluates to true, choose the All Generators

With Valid Display Filters option.

If you instead chose to read participation factors from a file, only those generators whose factors you read from the file

will have their factors set by this action. However, unless each generator’s associated area is set to control generator

output using participation factor control, this information will be ignored. To make sure that each generator’s area is

set to participation factor control, check the Set Corresponding Areas to Participation Factor Control box. Then,

each corresponding area will be set to participation factor control.

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Solving and Simulating a Case

Transactions

Area Transaction Modeling

One of the primary benefits of interconnected power system operation is the ability to do power transactions between

areas. In its simplest form, a power transaction entails one area selling a specific amount of power for a time period

(often specific, sometimes not) at a specific price to another area.

Simulator offers two complimentary mechanisms for specifying area interchange: Base Area Interchange and

Scheduled Area Interchange. These mechanisms may be used simultaneously, provided you understand that the use

of base transactions in economic studies can skew results considerably. This discussion should clarify the issues

involved in using the two types of transactions.

Base Area Interchange

The base interchange for an area is the amount of power (in MW) scheduled to be exported from the area to either

another area or to an unspecified buyer(s). However, since base interchange is intended only for use in standalone

power flow studies, no start/end times and no price are associated with the transaction. Since no price is specified,

from an economic modeling point of view the area is essentially giving the power away for free. This can, of course,

have a major impact on area economics. Additionally, base interchange has no starting or stopping time; it is

always assumed to be active.

However, the use of base interchange is convenient when you are simply doing power flow studies/simulations, as

long as the economic ramifications of the interchange is of no concern. Base interchange values can be set on the

Area Dialog. Please note that when you use base interchange with unspecified buyers, it is your responsibility to

ensure that the net of all base transactions add to zero. That is, in order for some areas to export, other areas must

be importing a corresponding amount. Base interchange values can also be viewed and modified on the onelines

using area fields.

Scheduled Area Interchange

The scheduled interchange for an area is the amount of power (in MW) scheduled to be sold from the area to

specific buying areas for a specific duration and price. You should use these types of transactions exclusively when

you are doing economic/pricing studies/simulations. The only downside to the use of scheduled interchange is that

you must specifically set up each such transaction. Please see MW Transactions Display for a description of how

to do this.

If the total interchange (base and scheduled) in the case do not sum to 0, Simulator will prompt you with a warning in

the message log. This means that Simulator will automatically find the area that contains the system slack bus and

turn it off of AGC controlArea_Control. The system slack bus w ill then account for the difference between the total

imports and the total exports defined in the case.

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Solving and Simulating a Case

Transaction Dialog

The Transaction Dialog can be used to modify or create Base Interchange Transactions between two areas. This

dialog can be opened by right-clicking in the Base Interchange table of the Area Information Dialog and choosing

Show Dialog to see an existing transaction definition, or Insert to add a new transaction.

The transaction dialog is divided into two pages of controls:

Information

Exporting Area

This is the "from" area for the transaction. For an export from this area, the transaction value will be positive. For

an import into the Exporting Area, the transaction value specified would be negative. Flow out (export) of the

exporting area is always considered positive.

Importing Area

This is the "to" area for the transaction.

Transaction ID

New in Simulator version 10 is the ability to have multiple transactions defined between the same two areas.

Because of this, it is now required that transactions also have a Transaction ID.

Rename Transaction ID

If you wish to change the transaction ID for a particular transaction, enter the new value in the Transaction ID field,

and press this button.

Switch Directions

Press this button if you wish to reverse the defined Exporter and Importer for the transaction.

Transaction MW Amount

The MW amount of the transaction being defined. This value should be positive for an export from the Exporting

area to the Importing area. The value can also be entered as negative to define a transaction into the Exporting

area from the Importing area.

Transaction Minimum MW

The minimum transaction amount between the two areas. This field is only enabled if the check box labeled

Transaction Dispatchable in OPF is checked.

Transaction Maximum MW

The maximum transaction amount between the two areas. This field is only enabled if the check box labeled

Transaction Dispatchable in OPF is checked.

Transmission Charge

The cost to transfer power, in $/MWh. This adds an economic penalty for making the transfer, making the transfer

less likely to take place. Half the charge is assigned to the buyer and half to the seller.

Transaction Enabled

Transaction can now be defined and either enabled or disabled. A ny disabled transactions will be ignored in both a

standard power flow solution and an OPF solution.

Transaction Dispatchable in OPF

Checking this box enables the transfer to be dispatched by the OPF algorithm. Dispatching the transaction makes

the two areas of the transaction appear to be one area for the purpose of economically dispatching the generation

in the two areas. The transaction can have a maximum and minimum transfer amount when dispatchable, and a

transmission charge associated with the trans action.

Determine Price in OPF

Checking this box allows the OPF algorithm to determine the cost associated with the transfer. The cost is

determined by the marginal cost of enforcing the power balance constraint for the combined areas. This is the

typical way to implement a transfer if both areas are on OPF control. If only one of the two areas are on OPF

control, then the area which is off of OPF control needs to specify a price for the transfer. This is done by explicitly

defining a piecewise linear c ost curve.

Piecewise Linear Transaction Cost Curve

These two curves are only enabled if the option Transaction is Dispatchable in OPF is checked and the option

Determine Price in OPF is unchecked. These two curves can be defined for the purpose of assigning a price to

the transfer of power between one area on OPF control and another area which is not on OPF control. Separate

curves can be defined for export transactions (from the Exporter to the Importer) and import transactions. To add

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PowerWorld Simulator version 11. Manual - page 12