PowerWorld Simulator version 11. Manual

SCOPF All LP Variables

The SCOPF All LP Variables dialog displays the basic and non-basic variables associated with the final LP SCOPF

solution. Users interested in the specifics of the LP SCOPF can access this page to obtain internal information about

the SCOPF solution. To see the display, open the Security Constrained Optimal Power Flow form, click on the LP

Solution Details tab, and access the All LP Variables page.

Right click any where in the display to copy a portion or all of the display to the Window's clipboard, or to print the

results.

The display lists each of the LP variables with the following fields:

Variable identifier.

Org. Value

The initial value of the LP variable before SCOPF optimization.

Value

The final value of the LP variable after SCOPF optimization.

Delta Value

The difference between the original value field and the value field.

Basic Var

Shows the index of the basic variables in the LP basis. If the value is zero, the variable is non-basic. These values

are set up after the SCOPF calculates the contingency violation sensitivities.

NonBasicVar

Shows the index of the non-basic variable. If the value is zero, the variable is basic.

Cost(Down)

The cost associated with decreasing the LP variable. The field will show if the variable is at its max or min limit.

Cost(Up)

The cost associated with increasing the LP variable. The field will show if the variable is at its max or min limit.

Down Range

The available range to decrease the basic variable before a new constraint is hit under a contingency condition.

Up Range

The available range to increase the basic variable before a new constraint is hit under a contingency condition.

Reduced Cost Up

The cost reduction that would be experimented if a LP variable increases. If a constraint is at the limit, the field

shows the change in cost of constraint enforcement.

Reduced Cost Down

The cost reduction that would be experimented if a LP variable decreases. If a constraint is at the limit, the field

shows the change in cost of constraint enforcement.

At Breakpoint

Yes, if the LP variable is at a break point.

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SCOPF LP Basic Variables

The LP Basic Variables (from the SCOPF LP Solution Details page) displays the basic variables of the final LP

solution. The basic variables may correspond to controls that can be altered to minimize the objective function, or

slack variables associated with unenforceable constraints. Users interested in the specifics of the LP SCOPF can

access this page to obtain internal information about the SCOPF solution. Right click any where in the display to copy

a portion or all of the display to the Window's clipboard, or to print the results.

The display lists each LP variable with the following fields:

Basic variable identifier.

Org. Value

The initial value of the basic LP variable before the SCOPF optimization.

Value

The final value of the basic LP variable after the SCOPF optimization.

Delta Value

The difference between the original value field and the value of the basic variable.

Basic Var

Shows the indices of the basic variables in the LP basis.

Cost(Up)

The cost associated with increasing the basic variable.

Down Range

The available range to decrease the basic variable before a new constraint is hit under a contingency condition.

Up Range

The available range to increase the basic variable before a new constraint is hit under a contingency condition.

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SCOPF Example: Introduction

In this section we introduce an example of using the SCOPF. Consider the seven bus, three area system contained in

the file B7SCOPF (included with the PowerWorld Simulator). This case is the same case used in the OPF example,

except that the line from bus 2 to 3 has now a 100MVA rating, lines 1 to 2, 1 to 3 and 2 to 5 have a 120MVA rating,

and all three areas are initially on OPF control. To initially solve the case using the optimal power flow, select Primal

LP under LP OPF. The solution obtained is shown in Figure 1. The total case hourly cost is $ 13,372 / hr.

We are interested in determining an optimal solution that meets security constraints under contingency conditions. In

order to show that the current OPF solution does not enforce contingency violations, take line 1 to 2 out of service by

clicking in a circuit breaker. Then solve the power flow by pressing the Single Solution button. The result in Figure 2

indicates that line 1 to 2 is overloaded 32%. The SCOPF algorithm will attempt to move the operating solution such

that no contingency violation occurs in the system. Close line 1 to 2 back in service.

The next step is to specify the contingency conditions that the system should withstand. In order to do that, we access

the Contingency Analysis dialog under Tools . Note that we can also access this dialog from the SCOPF control

dialog by selecting LP OPF > Security Constrained OPF and pressing the View Contingency Analysis Form button

on the Options page. The B7SCOPF case does not have contingencies assoc iated with it. Insert single line

contingencies in the contingency list by pressing the Auto Insert button located at the bottom left of the Contingency

Analysis dialog. in the Auto Insert Dialog select the option for Single Transmission Line and select Numbers under

the Identify buses by field. Select Do Insert Contingencies. This will prompt to insert 11 single line contingencies

corresponding to all the lines in the system. Select Yes. You can now close the Contingency Analysis dialog.

Return to the Security Constrained Optimal Power Flow Form. You can set the SCOPF to use the OPF solution as

the base by selecting Solve base case using optimal power flow .

You can now solve the SCOPF by pressing the Run Full Security Constrained OPF. This will process the

contingency violations and iteratively solve the LP program and the power flow equations to minimize the objective

function and enforce equality and inequality constraints. The solution is shown in Figure 3. The total operating cost is

now $ 13,409. The increase in operating cost is due to enforcing security constraints. If a new contingency analysis is

performed using the optimal solution as the reference, it will be found that no contingency violations occur for the

contingencies in the list, i.e., branch flows are less than (or equal to) 100% in the post contingency condition. Thus,

the system meets all the specified constraints. You can analyze the SCOPF results by browsing the information in the

SCOPF tabs. Note that the CTG Constraints dialog does not show unenforceable constraints, but the branch

violation of line 2 to 5 due to the contingency 5 to 7 is now binding.

B7SCOPF Case Solved using OPF

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SCOPF Example: Unenforceable Constraints

Using the same example as above, reduce the MVA rating of line 2 to 5 to 90 MVA. The initial base case LP OPF

solution is the same as in the previous example. Consider the same contingency list. When the contingencies are

solved using the initial OPF solution as the reference, seven contingency violations need to be removed. The CTG

dialog after simulation is presented in the following figure.

CTG Dialog after SCOPF Solution

We note that the constraint from bus 2 to 5 under a contingency from 5 to 7 is unenforceable. There are not enough

system controls to enforce the contingency constraint. A $ 1,000 / hr cost is assigned to unenforceable constraints in

this case. The cost of not enforcing constraints can be specified in the OPF Constraint Options Dialog.

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PowerWorld Simulator Add-on Tools

Available Transfer Capability (ATC) Analysis

The ATC Analysis tool is only available if you have purchased the ATC add-on to the base Simulator package.

Contact PowerWorld Corporation for details about ordering the ATC version of Simulator.

Available Transfer Capability (ATC) analysis determines the maximum MW transfer possible between two parts of a

power system without violating any limits. Most often, this transfer is between two areas in the system.

Simulator’s ATC analysis makes use of several tools that are available elsewhere in Simulator. These include

· Power Transfer Distribution Factors (PTDFs): determine the linear impact of a transfer (or changes in power

injection) on the elements of the power system.

· Line Outage Distribution Factors (LODFs): determine the linear impact of a line outage on the elements of the

power system.

· Contingency Analysis: studies the impact of a list of contingencies on the power system.

· Limit Monitoring Settings: control which elements of the system are monitored for limit violations.

You do not directly use these other tools when using Simulator’s ATC analysis tool, but Simulator uses the settings

and algorithms in the background to determine ATC. Thus, it is helpful to be knowledgeable on their use, as it will help

you in interpreting the results of an ATC analysis.

· Simulator provides three methods of determining the ATC for a transfer direction. See : ATC Solution Methods

For information on how to use the Simulator ATC tool, see Available Transfer Capability Dialog.

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ATC Dialog

Available Transfer Capability Dialog

The Available Transfer Capability Dialog provides you an interface for performing and viewing the results of

Available Transfer Capability Analysis. ATC analysis is typically only done on the present power system state or

scenario (called Single Scenario ATC Analysis). Click here for information on performing multiple scenarios analysis.

To open the ATC Dialog, select Tools > Available Transfer Capability (ATC) from the main menu. The dialog opens

to the Single Scenario ATC Analysis version with the Options tab, Common Options sub-tab visible. Click on any of

the desired tabs at the top of the dialog for more information on the contents of each.

ATC Dialog

The ATC Dialog is divided in three tabs: Options tab, Analysis tab, and Result tab. In addition, it has the following

controls:

Save/Load Settings

ATC Analysis settings can be saved by selecting Save Settings on the ATC dialog. This allows you to repeat the

analysis without having to reconfigure the settings. Select Load Settings to retrieve previously saved settings.

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ATC Dialog: Options Tab

The Options Tab of the ATC Dialog is subdivided in three sub tabs: Common Options, Define Contingencies, and

Advanced Options. They have the following controls:

Common Options

Seller Type, Buyer Type

For the ATC Solution Method of Single Linear Step (SL), ATC can be calculated for transfers between combinations

of areas, zones, super areas, injection groups, buses, or to a slack bus. For other ATC Solution Methods, ATC can

be calculated for transfers between areas, super areas or injection groups only. Use the seller type and buyer type

options to indicate the type of the selling and purchasing entities.

Seller, Buyer

These dropdown boxes allow you to select the selling and buying entities. The contents of each depend on the

Seller/Buyer Types selected. Clicking the Find Seller and Find Buyer buttons allows you to use Simulator’s

Advanced Search Engine to locate the desired entities.

Reverse Buyer/Seller Button

Click this button to reverse the direction currently shown. The buyer becomes the seller, and the seller the buyer.

Linear Calculation Method

The ATC analysis tool can use either a Lossless DC or Lossless DC with Phase Shifters calculation method for

obtaining the ATC results.

If you select the Lossless DC option, branch flow sensitivity is calculated by estimating the real power that flows

through the monitored element only from the differenc e in angles measured across its terminals.

The Lossless DC with Phase Shifters method, a modification to the lossless dc approximation, takes into account

phase shifter operation. It is especially useful when the ATC tool continually reports overloads on branches that

obviously will not overload because of the operation of a phase shifting transformer.

The Linearized AC method is not yet available.

Include Contingencies Check Box

Check this box to include contingencies (inserted or loaded using the Contingency Analysis Tool) in the ATC

analysis. Note that minimizing the number of contingencies considered greatly improves solution speed as well as

computer memory requirements for doing ATC Analysis. Therefore, be careful in choosing which contingencies to

use with the ATC tool.

Report Base Case Limitations Check Box

When checked, the ATC tool will report transfer limitations from the base case.

Report Generation Reserve Limitations Check Box

When checked, the ATC tool will report transfer limitations from generation reserve.

Limit Monitoring Settings Button

Click this button to open the Limit Monitoring Settings Dialog. Note that minimizing the number of monitored power

system elements greatly improves solution speed as well as computer memory requirements for doing ATC

Analysis.

Transfer Results Reporting Options

Transfer Limiters to Save

This value tells Simulator how many total "Transfer Limiters" to save. Simulator will save those Transfer

Limiters with the lowest Transfer Limitation. An explanation of a Transfer Limiter follows

During Linear ATC Analysis, Simulator determines the "Transfer Limitation" (See Available Transfer Capability

Analysis) for each transmission line and interface during each contingency and the base case. From this

Simulator develops a list of Transfer Limiters. A Transfer Limit contains three pieces of information

· Transfer Limit in MW

· Transmission branch (or interface) that causes the limit

· Contingency that is applied to cause the limit (if it’s a limit without any contingency applied, then the

contingency will say "Base Case")

Thus if we are monitoring 1000 transmission lines during 99 contingencies plus 1 base case, there would be

100,000 Transfer Limiters calculated. We are not concerned with all 100,000 limitations, theref ore, only the

limitations with the smallest Transfer Limit in MW are reported.

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Max Limiters per CTG

When analyzing a long list of contingencies, the worst transfer limitations may all occur during the same

contingency. Set this value to limit the number of Transfer Limiters saved that are associated with one

contingency.

Max Limiters per Element

Also, when analyzing a long list of contingencies, the worst transfer limitations may all be overload the same

limiting element. Set this value to limit the number of Transfer Limiters saved that are associated with one

Limiting Element.

Max MW Limitation

This value defines the maximum transfer to report between the buyer and seller. Simulator will compute the

ATC analysis results until the transfer amount reaches the value in this field, and only report the results meeting

the other reporting criteria up to this MW limitation.

Ignore Elements with OTDFs below

Simulator will not report Transfer Limitations for elements with OTDF values (or PTDF values if there is no

Limiting Contingency) less than this user-specified value. The default value is 0.5%, meaning that for 100 MW

transfer, there would be only a 0.5 MW increase in flow on the Limiting Element.

As described in Available Transfer Capability (ATC), the transfer limitation functions involve dividing by the

PTDF or OTDF values for each branch or interface. This leads to two facts:

· The accuracy of the transfer limitation is less for lines that have very small PTDF or OTDF values.

· A very small PTDF or OTDF value means that the transfer has very little impact on the line anyway.

These two facts often result in Linear ATC analysis reporting inaccurate transfer limitations for lines that are

largely unaffected by the transfer. It is not uncommon to have a transfer limitation report an extremely negative

transfer limit (e.g. -1.9E28 MW). A branch which is overloaded by a very small percentage, but which has a

very small OTDF value often causes this. If the OTDF value is 0.001%, then a branch overloaded by 1 MW will

result in a tranfer limitation of -100,000 MW.

This motivates the usefulness of ignoring elements with small PTDFs.

Ignore Elements with PTDFs below

Simulator will not report Transfer Limitations for elements with PTDF values less than this user-specified value.

The default value is 0.5%.

Define Contingencies

The Define Contingencies tab is similar to the Contingencies Tab of the Contingency Analysis Dialog. The user can

insert, auto-insert, define and/or delete contingency records. See Contingency Analysis for detailed information on

defining contingencies.

Advanced Options

ATC Solution Method

One of the solution methods of determining the ATC for a transfer direction.

Define Extra Monitors

Simulators ATC tool determines the maximum amount of MW transfer between the buyer and seller. If you would

like to also determine the flow on additional lines or interfaces at the transfer levels determined by the ATC tool, you

can utilize Extra Monitors. Click the Define Extra Monitors button to open the ATC Extra Monitors Dialog.

Analyze Multiple Scenarios

Check Analyze Multiple Scenarios to perform ATC Analysis on several scenarios. See

ATC Dialog for Multiple Scenarios for more information on Multiple Scenario Analysis.

Model Reactive Power for Linear Methods By…

The linearized methods used in ATC are based only on the changes in real power MW in the system, thus an

assumption needs to be made about the reaction of the Mvar flows during the linear calculations. The choices are

Ignoring reactive power, Assuming constant voltage magnitude, or Assuming reactive power does not

change .

For Linear Methods, Allow Amp Limits by Assuming a Constant Voltage Magnitude

If checked, Simulator will allow converting MVA limits to Amp limits by assuming constant voltage magnitudes

based on the base case full AC load flow operating point just prior to the ATC linear calculations.

Transfer Calculation Methods

Note: The Transfer Calculation Options section is disabled if the Single Linear Step Solution Method is selected.

Transfer Tolerance

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PowerWorld Simulator Add-on Tools

This is the tolerance used using the Iterated Linear Step or (IL) then Full CTG Solution methods. The default is

10.

Max. Iterations

This is the maximum number of iterations used in the Iterated Linear Step or (IL) then Full CTG Solution

methods. The default is 10.

When Iterating, Ignore Limiters below

This value indicates a minimum transfer value for reporting the ATC analysis results. Any ATC results below

this value will not be displayed. In general, you do not want to use this option, as you are interested in all

transfer limitations during various contingencies. However, sometimes you may wish to ignore ATC results

below 0, as a negative ATC result signifies a base case overload or limitation under the given contingency

condition, prior to any additional transfer in the defined seller to buyer direction.

Transfer Limiters to Iterate on

This is the number of transfer limiters to iterate on in the Iterated Linear Step or (IL) then Full CTG Solution

methods. The default is 1.

Power Flow Solution Options

This button brings up the Power Flow Solution Options Dialog.

Define Contingency Solution Options

Click this button to open the Contingency Solution Options Dialog.

Use Specific Solution Options For Contingencies

When checked, the ATC tool will use the solution options defined by pressing the "Define Contingency Solution

Options" button for contingency analysis. When not checked, all solutions will use the options defined by

pressing the "Power Flow Solution Options" button.

Enforce OPF Constraints

This only affects the Iterated Linear or (IL) then Full CTG Solution Methods. When Enforce OPF Constraints is

checked, Simulator solves the Optimal Power Flow after each transfer increase.

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ATC Dialog: Analysis Tab

The Analysis Tab of the ATC Dialog is used to control the analysis process. The scrollable window displays a record

of user-initiated actions relating to the analysis.

Analysis Tab

The Analysis tab has the following controls:

Start Analysis

The Start Analysis button begins the ATC Analysis using the settings and options defined by the user in the ATC

Analysis Dialog. Progress of the ATC Analysis is shown in the scrollable pane of the ATC Dialog - Analysis Tab

window.

Abort Calculation

When using one of the iterative ATC Solution Methods, or while analyzing Multiple Scenarios, click this button to

Abort the calculation.

Note: This does not immediately abort the solution. Simulator must restore the system state before completing the

abort.

Show Log

Click this button to show the Power Flow Solution Message Log.

Restore Initial State

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ATC Extra Monitors Dialog

Simulator’s ATC tool determines the maximum amount of MW transfer between the buyer and seller. If you would like

to also determine the flow on additional lines or interfaces at the transfer levels determined by the ATC tool, then you

can utilize ATC Extra Monitors. To open the Extra Monitors dialog, click the Define Extra Monitors button on the

Advanced Options tab of the ATC Analysis Dialog

The ATC Extra Monitors Display lists all the ATC Extra Monitors defined. This list display is a Case Information

Display, and therefore has the same functionality as other common displays. See Adding and Removing Extra

Monitors.

Extra Monitors Dialog

The default fields shown on this display are:

ATC ExMon Desc

This is a description of the monitored value. Presently, this is always MW flow.

ATC ExMon Obj

The power system element that is being monitored. This will be either a transmission branch or an interface.

Monitor Limit

This is the MW limit of the element being monitored.

Relative Monitor

Set this to a positive value to further filter the Transfer Limitations reported on the Transfer Limiters Display. By

default, relative Monitor is set to none, and no additional filtering of limitations is performed. If this value is greater

than zero, then only Transfer Limitations that meet the following condition are included in the results.

OTDF

ExtraMon Rating

ELEMENT

RelativeMonitor

PTDF_ELEMENT

Element Rating

This provides a measure of how much an interface or branch is affected by the transfer relative to its MW limit.

Adding and Removing Extra Monitors

To delete an extra monitor, right-click on the desired record on the list display and select Delete .

To insert an Extra Monitor, right-click on the list display and select Insert. This opens the insert dialog.

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PowerWorld Simulator Add-on Tools

Multiple Scenario Available Transfer Capability Dialog

To perform Available Transfer Capability Analysis for several system scenarios, check Analyze Multiple Scenarios on

the Advanced Options tab of the Available Transfer Capability Dialog. When Analyze Multiple Scenarios is not

checked the available tabs are Options, Analysis and Result. When Analyze Multiple Scenarios is checked then the

following changes occur:

· Scenarios Tab appears

· Results Tab appears

· Result Tab is removed (replaced by Results)

Analyze Multiple Scenarios Dialog

By defining multiple scenarios, Simulator allows you to calculate ATC values for several different power system states

automatically. Scenarios can be modified along three axes:

· Line Rating/Zone Load Scenarios (weather-related scenarios)

· Generation Scenarios (generation profiles)

· Interface constraints

See Scenarios Tab for more information.

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Multiple Scenario ATC Dialog: Scenarios Tab

By defining multiple scenarios, Simulator allows you to calculate ATC values for several different power system states

automatically. Scenarios can be modified along three axes:

· Line Rating/Zone Load Scenarios (weather-related scenarios)

· Generation Scenarios (generation profiles)

· Interface constraints

Analyze Multiple Scenarios Dialog: Scenarios Tab

Each tab contains a list of the power system elements that will be modified during different scenarios. These lists are

a familiar Case Information Display providing the same functionality as other displays

To insert a new power system element into the list, right click on the list (below the headings) and choose Insert.

On each tab, you may enter how many different scenarios should be defined for that kind of power system element.

For instance if you set Generation Scenarios to 5, then list display on the Generation Tab will provide 5 columns

labeled G0, G1, G2, G3, and G4. Generation outputs should then be entered into each cell representing the

generation output in each scenario.

Once you have specified the scenarios, Simulator is able to perform ATC Analysis on every combination of the axes.

For example, assume you have the following:

10 sets of line ratings and zones load

8 sets of generation profiles

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3 interface constraints

This yields a total of 240 different scenarios to calculate (10*8*3 = 240 ). Be warned that that the more scenarios you

analyze the longer the computation will take.

Line Ratings and Zone Loads are varied together when analyzing scenarios. This was chosen because they often

vary together as a function of the weather. Notice that two sub-tabs (labeled Line Ratings and Zone Loads

respectively) appear at the bottom of the Line Ratings/Zone Loads tab.

The Scenarios Tab has the following controls:

Tabs and Sub-Tabs

The Scenarios Tab contains three tabbed sheets: Line Ratings/Zone Loads, Generator Outputs and Interface

Ratings.

Line Ratings and Zone Loads are varied together when analyzing scenarios. This was chosen because they often

vary together as a function of the weather. Notice that two sub-tabs (labeled Line Ratings and Zone Loads

respectively) appear at the bottom of the Line Ratings/Zone Loads tab.

Number of Defines Scenarios per Element Type

On each tab, you may enter how many different scenarios should be defined for that kind of power system element.

For instance if you set Generation Scenarios to 5, then list display on the Generation Tab will provide 5 columns

labeled G0, G1, G2, G3, and G4. Generation outputs should then be entered into each cell representing the

generation output in each scenario.

Total Scenarios

Once you have specified the scenarios, Simulator is able to perform ATC Analysis on every combination of the

axes. For example, assume you have the following:

10 sets of line ratings and zones load

8 sets of generation profiles

3 interface constraints

This yields a total of 240 different scenarios to calculate (10*8*3 = 240 ). Be warned that that the more scenarios

you analyze the longer the computation will take.

Set Scenario Names

This button will bring up the Scenario Names dialog, where the user is able to assign a different name to the

scenarios.

Assume Constant Power Factor

This option is only available in the Zone Loads sub-tab of the Line Ratings/Zone Loads tab. If selected, it specifies

that the Mvar will be ramped as the load MW are ramped, maintaining a constant power factor.

No Change in MVAR

This option is only available in the Zone Loads sub-tab of the Line Ratings/Zone Loads tab. If selected, it specifies

that the Mvar are kept constant, independently of the variations of the load MW.

Modified Elements

Each tab contains a list of the power system elements that will be modified during different scenarios. These lists

are a familiar Case Information Display providing the same functionality as other displays.

To insert a new power system element into the list, right click on the list (below the headings) and choose Insert.

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Multiple Scenario ATC Dialog: Results Tab

Once you have defined your scenarios and started the ATC Analysis, you can switch to the Results Tab to see the

progress that ATC Analysis is making. Click on the diagram below for specific information on the contents of the

Results Tab.

Multiple Scenario Results Tab

The primary part of the Results tab contains a spreadsheet-like look-up table display. The layout of the display is

dictated by the Axis Order selected. See Local Menu Options for information regarding the Results Tab local menu.

This dialog has the following controls:

Show Transfer Limiters Button

Click the Show Transfer Limiters button to view the Transfer Limiters found under each scenario. This will open a

separate dialog that displays a list of the Transfer Limiters. To see the Transfer Limiters for a particular scenario,

click on the workbook cell that represents the scenario you are interested in and the separate dialog will update

appropriately.

Axis Order

This menu is used to select the desired axis order. The three axes correspond to the three Scenarios Tabs.

· One axis has heading labels G0, G1, … for the Generation Scenarios,

· Another with heading labels RL0, RL1, … for the Rating/Load Scenarios,

· A third with heading labels I0, I1, … for the Interface Scenarios.

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Multiple Scenario ATC Analysis - Results Tab: Local Menu Options

If you right click on the workbook, you will bring up a local menu containing several options. The first several options

are only enabled if you right click on a cell representing a scenario. These options will perform an operation with

respect to the Scenario:

Take me to Scenario …

Will make modifications to the system state to take you to the Scenario.

Determine Transfer Limit For Scenario …

Will calculate the ATC for the Scenario, and then take you back to the Initial State.

Take me to the Transfe r Limit For Scenario …

Will perform ATC for the Scenario, and then ramp the transfer to this limit.

Other options on this local menu are not related to the Scenario you have clicked on.

Increase Transfer for Present System State

Will increment the transfer level for the present system state by a user-defined amount.

Return to Initial State

Will return the system state to the Initial State.

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Transfer Limiters Display

The Transfer Limiters Display shows the results of ATC Analysis. This display appears either on the Result Tab of the

Available Transfer Capability Dialog or as a separate window when performing Multiple Scenario Available Transfer

Capability Analysis.

The display contains four different tabs: All Limiters, Branch Limiters, Interface Limiters, and Nomogram Interface

Limiters. Click the respective tabs below to find more information on each.

The list displays shown on each tab are instances of Case Information Displays. The default fields displayed are

shown below. Click on the respective columns on the list display below to view specific information about the display

fields.

The Contingency Definition Display at the bottom of the window shows information on the defined contingency that

caused the limitation selected from one of the four tabbed pages of limiters. For more information on this display, see

Contingency Analysis - Contingency Definition Display.

Transfer Limiters Display

The Transfer Limiters Display has the following controls:

All Limiters Tab

The All Limiters tab shows a list of all the transfer limitations found. This includes limitations on branches,

interfaces, areas, zones, etc…

Branch Limiters Tab

The Branch Limiters tab only shows those limitations with a transmission line or transformer as the limiting element.

The limiting element description for the Branch Limiters tab is replaced by the bus numbers and names of the

limiting element.

Interface Limiters Tab

The Interface Limiters Tab only shows those limitations with an interface as the limiting element. The limiting

element description is replaced by the name of the interface.

Nomogram Interface Limiters Tab

The Nomogram Interface Limiters Tab only shows those limitations with a nomogram interface as the limiting

element. The limiting element description is replaced by the name and segment of the nomogram interface.

Limiters Fields

Transfer Limiter Field

The Transfer Limit Field shows the Transfer Limit in MW for the Limiting Element during the Limiting

Contingency. This value depends on the ATC Solution Method Used:

· Single Linear Step (SL): Only Only one Linear ATC step is performed. The Transfer Limitation values are

those found during this step.

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· Iterated Linear Step (IL): The Linear ATC method is iterated during this method. The Transfer Limiters

shown are those found during the final step performed. The actual Transfer Limitation values are the

values found at the last step plus the accumulated amount the transfer has been ramped. The Transfer

Limitation(s) that were used when iterating are highlighted in cyan.

· Iterated Linear Step (IL) then Full CTG: The Transfer Limiters shown are those found during the last

contingency analysis step that found violations. The Transfer Limitation values equal the accumulated

amount the transfer was ramped. Note that when performing the Full CTG Solution, negative ATC values

will not be probed, so the Transfer Limit will appear as 0 if there are violations in the Initial State. Any

Transfer Limiters that result in unsolvable contingencies are solved with the Single Linear step (SL) and

are highlighted in yellow .

Limiting Element Field

Shows a text description of the limiting element.

Limiting CTG Field

Shows the name of the limiting contingency.

% OTDF Field

This is the OTDF (or PTDF if the Limiting CTG is Base Case) on the Limiting Element for the transfer direction

that is being studied. In other words, this is a linear estimate of the percent of the transfer that will appear on

the Limiting Element if the Limiting CTG occurs.

Note: For Iterated Linear, this is the PTDF or OTDF at the last Linear Iteration. When using Full CTG Solution

Method, this is not calculated and will appear as 0 for all Limiters.

Pre-Transfer Value Estimate Field

If a contingency is not included in the Limiter, this is equal to the Initial Value. When a contingency is included

in the Limiter, this is the linear estimate of the post-contingency flow before any transfer occurs. See Available

Transfer Capability Analysis.

Note: For Iterated Linear, this is the estimate at the last Linear Iteration. When using (IL) Full CTG, this is not

calculated and will appear as 0 for all Limiters.

Limit Used Field

This is the value of the Limit being used by the ATC for the Limiting Element during the Limiting CTG. It reflects

what is specified in Limit Monitoring Settings.

Contingency Definition Display

This display shows information on the defined contingency that caused the limitation selected from one of the four

tabbed pages of limiters. For more information on this display, see Contingency Analysis - Contingency Definition

Display.

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ATC Analysis Methods - Single Linear Step (SL)

The Single Linear Step approach is the most common ATC method and duplicates the ATC analysis done by many

system reliability organizations throughout North America. This method of ATC analysis uses only information about

the present system state and sensitivities (mathematical derivatives) about the present system state. These

sensitivities are embodied in the PTDF and LODF calculations.

Consider a transmission line with a limit of 10, present loading of 5 and a PTDF of 10%. The estimated maximum

transfer without causing on overload on line is

Transfer Limitation = (Limit - Present Loading) / PTDF = (10 - 5) / 0.1 = 50 MW

When including contingency analysis, the OTDF (Outage Transfer Distribution Factor) and linearized estimates of

post-contingency flows are used to determine the Transfer Limitation.

Transfer Limitation = (Limit - Post-Contingency Loading) / OTDF

If we find the Transfer Limitation for every transmission branch (and interface) during each contingency, then the ATC

is equal to the smallest Transfer Limitation.

Note: Simulator also monitors the possibility that a transfer will reduce the flow on a line until the line reaches its limit

for flow in the opposite direction.

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PowerWorld Simulator Add-on Tools

ATC Analysis Methods - Iterate d Linear Step (IL)

The Single Linear Step is an extremely fast method for determining the ATC. However, because it only uses present

operating point information, controller changes are not taken into account. The linearization assumes that all

controllers are fixed. The Iterated Linear Step (IL) method provides an alternative to the Single Linear Step, but still

performs its analysis in a reasonable amount of time. The (IL) method operates as follows

· Stepsize = ATC using Single Linear Step (Note: save this initial step size for use by the Full CTG Solution)

· If [abs(stepsize) < Tolerance] then stop

· Ramp transfer out an additional amount of Stepsize and resolve Power Flow

· At new operating point, Stepsize = ATC using Single Linear Step

· Go to step 2

This method takes into account controller changes that occur as you ramp out to the transfer level, but still avoids the

full simulation of contingencies.

This method can be applied between combinations of areas and super areas, OR between two injection groups.

Combinations of areas/superareas and injection groups are not allowed.

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ATC Analysis Methods - Iterated Linear Step (IL) then Full CTG Solution

If you want to absolutely test the validity of the ATC number, then you can use this method. Be aware however, that

this calculation method can be extremely slow. The (IL) then Full CTG Solution method operates as follows.

1 Run Iterated Linear Step and ramp transfer out ATC Value found

2 Stepsize = 10% of the initial Linear Step Size saved during the (IL) method, or 50 MW whichever is larger.

3 Run Full Contingency Analysis on the ramped transfer state

4 If there are violations then change the sign of Stepsize

5 if [abs(stepsize) < Tolerance] then Stop

6 Ramp transfer out an additional amount of Stepsize and resolve Power Flow

7 At new operating point, Run Full Contingency Analysis

8 IF [ (Stepsize > 0) AND (Violations) OR (Stepsize < 0) AND (NO Violations) ]

THEN Stepsize := -Stepsize/2 (switch direction)

9 Go to step 5

This method can be applied between combinations of areas and superareas, OR between two injection groups.

Combinations of areas/superareas and injection groups are not allowed.

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PowerWorld Simulator Add-on Tools

Simulator Automation Server (SIMAUTO)

Simulator Automation Server (SimAuto) Overview

The SimAuto tool is only available if you have purchased the SimAuto add-on to the base Simulator package.

Contact PowerWorld Corporation for details about ordering the SimAuto version of Simulator.

PowerWorld Corporation also offers Optimal Power Flow (OPF), Available Transfer Capability ATC, Simulation

Automation Server (SimAuto), and Security Constrained Optimal Power Flow (SCOPF) add-ons. For more information

see PowerWorld Simulator Add-On Tools.

SimAuto provides PowerWorld customers the ability to access PowerWorld Simulator functionality within a program

written externally by the user. The Simulator Automation Server acts as a COM object, which can be accessed from

various programming languages that have COM compatibility. Examples of programming tools with COM compatibility

are Borland‚ Delphi, Microsoft‚ Visual C++, Microsoft‚ Visual Basic, and Matlab‚ (among others). For more

information on COM Objects and Automation Servers, see the help for Microsoft Windows.

The Automation Server of Simulator works very well in combination with Simulator Script Commands and Auxiliary

Files. It is beneficial to become familiar with these topics when considering using the Simulator Automation Server.

Note that previous users of SimAuto in Version 9 will need to update their function calls to SimAuto functions.

PowerWorld Corporation found it imperative to change the function calls for SimAuto, in order to remedy irreconcilable

problems when using SimAuto with some programming languages. The documentation provided should provide

adequate help on the changes needed, but as always, if any questions arise, please contact PowerWorld Corporation

for more information.

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Starting Simulator Automation Server

Installing Simulator Automation Server

Note that previous users of SimAuto in Version 9 will need to update their function calls to SimAuto functions.

PowerWorld Corporation found it imperative to change the function calls for SimAuto, in order to remedy irreconcilable

problems when using SimAuto with some programming languages. The documentation provided should provide

adequate help on the changes needed, but as always, if any questions arise, please contact PowerWorld Corporation

for more information.

Installing the Simulator Automation Server requires no additional steps beyond installing PowerWorld Simulator as

normal. When a version of PowerWorld Simulator containing the Simulator Automation Server is installed on your

computer, the install program automatically adds the information needed by the Simulator Automation Server to the

registry.

If for some reason the registration fails, be sure you have the SimAuto add-on for Simulator and you have either run

the application on the computer or run the command pwrworld / regserver at the command line. If instead you would

like SimAuto to un-register itself as a COM object, run the command pwrworld /unregserver at the command line.

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PowerWorld Simulator Add-on Tools

Including Simulator Automation Server Functions

Before you can access the functions defined by the Simulator Automation Server when writing the code for your

external program, you must first include the library of functions defined for the Simulator Automation Server. This kind

of library is referred to as a Type Library, which describes the available functions in a manner that can be interpreted

by different programming languages. Importing a Type Library from another program is usually fairly simple, but the

procedure does vary depending on the programming tool you are using. Please see the help for your programming

tool of choice on how to import a Type Library or COM functions from another program.

Examples

The following examples are just a few specific examples for certain programming media. The procedure may be

different for other programming media not listed. In addition, a procedure given for a certain type of programming

media may be one variation from several possible procedures for accomplishing the same task.

Borland Delphi

· Install the version of PowerWorld Simulator with the Simulator Automation Server included.

· In Delphi, choose Import Type Library… from the Project menu.

· In the list of libraries, search for and choose pwrworld Library.

· If pwrworld Library is not in the list, click Add. Find and choose the Pwrworld.exe file from the PowerWorld

Simulator directory, and click Open.

· You should see the class name TSimulatorAuto in the list of Class names.

· Click Install to include the PowerWorld Simulator Type Library.

Microsoft Visual Basic for Applications

· No additional tasks are necessary

· Importing Type Library still works (See Including Functions for version 9).

Microsoft Visual C++

· Install the version of PowerWorld Simulator with the Simulation Automation Server included.

· Add #import "…\powerworld.exe" in your external program code, using the full path to the PowerWorld

Simulator executable program.

· Add using namespace pwrworld in your external program code.

Matlab v.6.5 r.13

· No additional tasks are necessary.

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Connecting to Simulator Automation Server

Once the Type Library or COM functions have been included in your programming environment, the Simulator

Automation Server can be handled as any other object in your code. The method for assigning and connecting to the

Simulator Automation Server can vary depending on the programming environment used, but the idea is basically the

same. You define a variable in your program to point to the server object, which is called SimulatorAuto. If the Type

Library was imported properly, you should have full access to the SimulatorAuto object and its defined functions.

Again, the procedure for creating the object and connecting to SimulatorAuto may vary for different programming

languages. Check the help for your programming environment on connecting to COM or Automation servers.

Examples

The following examples are just a few specific examples for certain programming media. The procedure may be

different for other programming media not listed. In addition, a procedure given for a certain type of programming

media may be one variation from several possible procedures for accomplishing the same task.

Borland Delphi 5

· Add pwrworld_TLB to the uses section of your unit.

· Declare a variable globally or as part of another object: A : ISimulatorAuto

· Initialize the variable: A := nil

· To connect to the Simulator Automation Server, create the connection: A := CoSimulatorAuto.create

· Perform function calls to the Simulator Automation Server: Output := A.SomeFunction(parameters)

· To close the connection to the Simulator Automation Server, remove the reference by again setting: A :=

nil

Microsoft Visual Basic for Applications

Early Binding:

· To connect to the Simulator Automation Server, create the connection initializing the variable:

Dim A as New pwrworld.SimulatorAuto

Late Binding:

· Declare a variable globally or as part of another object or function: Dim A As Object

· To connect to the Simulator Automation Server, create the connection:

Set A = CreateObject("pwrworld.SimulatorAuto")

Both Early and Late Binding:

· Perform function calls to the Simulator Automation Server: Output = A.SomeFunction parameters

· To close the connection to the Simulator Automation Server, remove the reference: Set A = Nothing

· If Type Library was imported, connection can also be achieved as in version 9 (See Connecting to

Simulator Automation Server in version 9).

Microsoft Visual C++

· Declare a variable globally or as part of another object or function: IsimulatorAutoPtr *A

· Declare a variable globally or as part of another object or function: CLSID clsid

· Declare a variable globally or as part of another object or function: HRESULT hr

· Obtain the class identifier (clsid) with the following command:

hr = CLSIDFromProgID(L"pwrworld.SimulatorAuto", &clsid)

· Initialize variable A: A = new IsimulatorAutoPtr

· To connect to the Simulator Automation Server, create the connection:

hr = A>CreateInstance(clsid, NULL, CLSCTX_SERVER)

· Perform function calls to the Simulator Automation Server: Output = A.SomeFunction(parameters)

· To close the connection to the Simulator Automation Server, release the reference:

hr = A>Release()

Matlab v.6.5 r.13

· To connect to the Simulator Automation Server, create the connection:

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PowerWorld Simulator Add-on Tools

Getting Data from the Simulator Automation Server

The Output Structure

Every function called on the SimulatorAuto object returns the same value, Output, which has a well-defined structure.

Output is of type VARIANT, and is an array of VARIANT’s. Output is zero-indexed.

The first element always contains any errors occurring during execution. For those functions returning more than one

element in the Output array (e.g. ListOfDevices), explanation is provided below when discussing the specific method.

Error Handling

As mentioned above, the first item in the Output VARIANT array, Output[0], contains any errors occurring during the

function’s execution. If no errors occurred during the function’s execution, Output[0] will be set to an empty BSTR

(string) represented in most languages by either ‘’ or "".

Error Format

If an error string is returned, it will be in the following format:

[method name]: [error_explanation]

e.g. RunScriptCommand: Error occurred processing script command - check command syntax

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PowerWorld Simulator Add-on Tools

ChangeParameters Function

The ChangeParameters function allows you to set a list of parameters for a specific object in a case loaded into the

Simulator Automation Server. In addition to changing parameters for objects, this function can also be used to set

options for some of the Simulator tools, such as ATC and OPF. This function is identical in setup to the

GetParametersSingleElement function, with the exception that the Values array must contain a value for each field

variable given in the ParamList array.

Function Prototype

ChangeParameters(ObjectType, ParamList, Values)

Parameter Definitions

ObjectType : String

The type of object you are changing parameters for.

ParamList : Variant

A variant array storing strings (COM Type BSTR). This array stores a list of

PowerWorld‚ object field variables, as defined in the section on PowerWorld

Object Fields. The ParamList must contain the key field variables for the

specific device, or the device cannot be identified.

Values : Variant

A variant array storing variants. This array can store any type of information

(integer, string, etc.) in each array position. A value should be passed for each

field variable given in the ParamList. The Values array must contain the key

field values for the specific device, or the device cannot be identified.

Output

ChangeParameters only returns the first element in Output, the error string.

Notes

The ParameterList and Values arrays must be the same size, as each parameter must have a corresponding

value to be assigned.

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ChangeParameters Function: Sample Code

Borland® Delphi

Var ParamList, ValueList : OLEVariant

// Set ParamList up to modify the maximum number of iterations

// and the system base for the power flow simulations

ParamList := VarArrayCreate([1,2], varOleStr);

ParamList[1] := 'MaxItr';

ParamList[2] := 'SBase';

// ValueList is setup with 41 and 410 for MaxItr and SBase,

// respectively

ValueList := VarArrayCreate([1,2], varOleStr);

ValueList[1] := 41;

ValueList[2] := 410;

// Make the ChangeParameters call

Output = SimAuto.ChangeParameters('Sim_Solution_Options', _

ParamList, ValueList)

Microsoft® Visual Basic for Applications

' Set ParamList up to modify the maximum number of iterations

' and the system base for the power flow simulations

Dim ParamList As Variant

ParamList = Array("MaxItr", "Sbase")

' ValueList is setup with 41 and 410 for MaxItr and SBase,

' respectively

Dim ValueList As Variant

ValueList = Array(45, 90)

' Make the ChangeParameters call

Output = SimAuto.ChangeParameters("Sim_Solution_Options", _

ParamList, ValueList)

Matlab®

% Set ParamList up to modify the maximum number of iterations

% and the system base for the power flow simulations

ParamList = {'MaxItr' 'Sbase'};

% values is setup with 41 and 410 for MaxItr and SBase,

% respectively

values = [41 410];

% Convert the values matrix to a set of cells for passing

% through the COM interface

ValueList = num2cell(values);

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PowerWorld Simulator version 11. Manual - page 19