PowerWorld Simulator version 11. Manual

PowerWorld Simulator Add-on Tools

OPF Options : Solution Results

The OPF Dialog, Solution Results page displays general results from the last OPF solution. The display contains the

following fields, none of which can be directly changed:

General Results

Solution Start Time, Solution End Time

The starting time and ending time of the OPF solution algorithm.

Total Solution Time, Last Solution Status

Time and status of the last OPF solution.

Number of LP Iterations

Total number of LP iterations used during the last OPF solution. The maximum number of iterations are specified in

the Maximum Number of Iterations field of the General Options page.

Initial Cost Function Value

Initial value of the OPF cost function. During the OPF the solution algorithm seeks to minimize the cost function,

subject to the equality and inequality constraints.

Final Cost Function Value

Final value of the OPF cost function.

Final Slack Cost Value

The slack cost value is an artificial cost that is only non-zero when there are one or more unenforceable constraints.

Final Total Cost Value

The addition of the final cost function value and the final slack cost value.

Number of Buses in OPF

This field contains the total number of buses that are in areas or super areas that are on OPF control. Thus this

field need not be equal to the total number of buses in the case. Marginal costs are only calculated for buses in

OPF controlled areas or super areas.

Highest Bus Marginal Cost, Lowest Bus Marginal Cost, Average Bus Marginal Cost

Highest, lowest and average marginal cost for the buses that are in OPF controlled areas or super areas.

Bus MC Standard Deviation

The standard deviation of the Bus Marginal Cost.

Line MVA Constraints

The Line MVA Constraints fields present results associated with the enforcement of the line MVA constraints.

Number of Initial Violations, MVA Sum of Initial Violations

Total number of lines that initially exceeded their MVA limits and were eligible for enforcement by the OPF. For

these lines only, the MVA Sum of Initial Violations field contains sum of the absolute values of the line's actual

MVA flow minus the line's MVA limit.

Number of Binding Lines

Total number of lines that are constrained to their limit value.

Highest Line MVA Marginal Cost

The highest Marginal Cost for an MVA change on a line.

Number of Unenforceable Violations

Total number of lines whose MVA flows can not be enforced by the OPF using the available controls.

MVA Sum of Unenforceable Violations

For all the unenforceable lines, this field contains the sum of the absolute values of the line's actual MVA flow minus

the line's MVA limit.

Interface MW Constraints

The Interface MW Constraints field present results associated with the enforcement of the interface MW constraints.

Number of Initial Violations, MW Sum of Initial Violations

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Total number of interfaces that initially exceeded their MW limits and were eligible for enforcement by the OPF. For

these interfaces only, the MW Sum of Initial Violations field contains sum of the absolute values of the interface's

actual MW flow minus the interface's MW limit.

Number of Binding Interfaces

Total number of interfaces that are constrained to their limit value.

Highest Interface MW Marginal Cost

The highest Marginal Cost for an MVA change on an interface.

Number of Unenforceable Violations

Total number of interfaces whose MW flows can not be enforced by the OPF using the available controls.

MW Sum of Unenforceable Violations

For all the unenforceable interfaces, this field contains the sum of the absolute values of the interface's actual MW

flow minus the interface's MW limit.

Area and Superarea Constraints

Unenforceable Area Constraints

Number of unenforceable area constraints.

Unenforceable Superarea Constraints

Number of unenforceable superarea constraints.

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PowerWorld Simulator Add-on Tools

OPF Options: All LP Variables

The OPF Dialog, All LP Basic Variables page displays the basic and non-basic variables associated with the final LP

solution. This page is usually only of interest to users interested in the specifics of the LP 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 of the LP variables, showing the following fields for each:

Variable identifier.

Original Value

The initial value of the LP variable before SCOPF optimization.

Value

The final value of the LP variable after OPF 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.

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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OPF Options: LP Basic Variables

The OPF Dialog, LP Basic Variables page displays the basic variables associated with the final LP solution. This page

is usually only of interest to users interested in the specifics of the LP 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 of the basic variables, showing the following fields for each:

Basic variable identifier.

Original Value

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

Value

The final value of the basic LP variable after the OPF 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(Down)

The cost associated with decreasing the basic variable.

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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OPF Records

OPF Area Records

Displays OPF specific information about each area record in the case. To show this display select LP OPF, OPF Area

Records . The OPF Area Records Display is a class of Case Information Display and therefore can be used in a

manner consistent with the other case information displays. Specific formatting options are available from the local

menu, which can be accessed by right-clicking on any field in the display. The columns can also be sorted by right-

clicking on the heading of the field.

By default the display contains the following fields:

Number, Name

Area’s number, between 1 and 999, and its alphanumeric identifier, eight characters maximum.

AGC Status

Area's automatic generation control status. This is the same field shown on the Area Records Display. The field

indicates whether or not the area's generation is changing automatically to control the area interchange.

To be included in the OPF, this field MUST be "OPF". The generation costs for areas that are on "OPF" control are

included in the OPF objective function; otherwise they are not. Note that if the area is part of a super area that is on

AGC control, this field value is ignored.

Double-click on the field to toggle its value.

XF Phase

Specifies whether phase shifting transformers in the area are available as controls. If "Yes" then all transformers in

the area which have their Automatic Control Active are available for control; the Automatic Control status for a

transformer is set on the Line/Transformer Dialog. If "No" then no transformers in the area are available for control.

Branch MVA

Specifies whether or not the MVA limits should be enforced for transmission lines and transformers that have at

least one terminal in this area. For a transmission line or transformer to be included Line/Transformer constraints

must not be disabled on the OPF Options Dialog, and the individual line/transformer must be enabled for

enforcement on the OPF Line/Transformer MVA Constraints display.

Interface MW

Specifies whether or not the MW limits should be enforced for interfaces that have at least one element in this area.

For an interface to be included Interface constraints must not be disabled on the OPF Options Dialog, and the

individual interfaces must be enabled for enforcement on the OPF Interface MW Constraints display.

Load MW Dispatch

Specifies whether or not the MW load demand in an area should be included as available for re-dispatch during an

OPF solution. In order for loads to be included in OPF re-dispatch, each individual load within the area must be

available for control, and have either a fixed cost benefit or a piecewise-linear cost benefit curve provided.

Include Marg. Losses

Specifies whether or not marginal losses should be included for the area during the OPF solution.

MW Marg. Cost Ave

For an OPF solved case this field shows the average of the bus MW marginal costs for all the buses in the area. If

there is no congestion then all of the marginal costs should be equal.

MW Marg. Cost St.Dev., Min., Max.

For an OPF solved case these fields show the standard deviation of the bus MW marginal costs for all the buses in

the area, the minimum and the maximum bus MW marginal costs.

Report Limits

Specifies whether or not the kV limits should be reported.

Report Min kV, Report Max kV

Specifies the values for minimum and maximum kV levels to report. Defaults are 0 and 9999.

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OPF Bus Records

Displays OPF specific information about each bus record with a valid area/zone/owner filter. To show this display

select LP OPF, OPF Bus Records. The OPF Bus Records Display is a class of Case Information Display and

therefore can be used in a manner consistent with the other case information displays. Specific formatting options are

available from the local menu, which can be accessed by right-clicking on any field in the display. The columns can

also be sorted by right-clicking on the heading of the field.

By default the display contains the following fields

Number, Name

Bus’s number, between 1 and 99,999, and its alphanumeric identifier, eight characters maximum.

Area Name

Name of the bus's area.

MW Marg. Cost

Marginal change in the objective function for a one MW change in the real power load at the bus.

MVR Marg. Cost

Marginal change in the objective function for a one Mvar change in the reactive load at the bus.

Volt Marg. Cost

Marginal change in the objective function for a 0.01 per unit change in the voltage setpoint for the bus. This field is

only valid at bus’s whose terminal voltage is controlled by one or more generators.

Note from the developers - this field is still under construction - do not use it yet.

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OPF Generator Records

Displays OPF specific information about each generator record with a valid area/zone/owner filter. To show this

display select LP OPF > OPF Generator Records . The OPF Generator Records Display is a class of Case

Information Display and therefore can be used in a manner consistent with the other case information displays.

Specific formatting options are available from the local menu, which can be accessed by right-clicking on any field in

the display. The columns can also be sorted by right-clicking on the heading of the field.

By default the display contains the following fields

Number, Name

Number and name of the bus to which the generator is attached. The display's local menu offers you the

opportunity to view the Quick Power Flow List and the Bus View Display for this bus. You can also use the local

men to view the generator's dialog.

Alphanumeric ID used to distinguish multiple generators at the same bus.

Area Name of Gen

Name of the generator's area.

AGC

Designates whether the generator's real power output is governed by automatic generation control (AGC). If the

AGC field is set to Yes the generator is on AGC in the standard power flow. When a generator is on AGC its real

power output is varied automatically, provided the generator is part of an area or super area that is also on

automatic control.

In Simulator OPF the default operating mode is that only generators on AGC control are eligible to be OPF controls.

In addition, the generator's area or super area must have AGC Status of "OPF". However in rare instances you

may wish to always make a generator available for control or never make the generator available for control. This

value is specified using OPF MW Control field.

Fast Start

Designates whether the generator is available as a Fast Start generator during the OPF solution process. Fast start

generators are another type of control available to the Optimal Power Flow solution routine. The OPF routine can

determine if a generator labeled as a fast start generator would be beneficial in reducing the overall system costs of

generation dispatch. If a fast start generator is off-line, but could reduce the cost of the system, then the OPF

routine will turn on the generator, and increase the generator's dispatch towards optimizing the system generating

cost. Conversely, if a fast start generator is on-line, and the OPF routine determines that reducing the generator's

output to 0 would reduce the total generation cost, then the OPF routine will shut off the generator.

Generally speaking, the fast start options should only be used with units with zero Minimum MW limits. Hence it is

really aimed at hydro units, or small units which do not need a non-zero minimum MW output for valid operation.

This requirement is needed because changing a unit's status is only valid in the OPF routine if it is determined that

the unit should dispatch 0 MW to optimize the generating costs of the system.

OPF MW Control

Designates whether the generator's real power output should be included as a control variable in the OPF. This

field, which can be toggled, has three possible values:

· "If AGCable" - Generator's control availability depends upon its AGC status.

· "Yes" - Generator is available as a control, regardless of its AGC status.

· "No" - Generator is NOT available as a control, regardless of its AGC status.

Note: in order to be a control the generator must also be in an area or super area on "OPF" control.

Gen MW

The real power output of the generator.

Cost Shift $/MWh, Cost Multiplier

The cost shift and cost multiplier allow you to easily apply a shift to the cost function for the purpose of assessing

how variations in bids impact profit. The cost function is affected based on the following equation:

(Original Cost Function + Cost Shift) * Cost Multiplier

Cost $/Hr

The total cost of the generator, including the impact of the cost shift and cost multiplier.

MW Marg. Cost

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Tells the marginal cost, in $ / MWhr, to supply one additional MW of load at this bus. If a generator is available as a

control and is not at either its minimum or maximum limit or a cost model breakpoint, then the MW Marg. Cost field

will be identical to the generator's current marginal cost. However the usual case is for the generator to be at either

a limit or a cost model breakpoint so the usual situation is that the MW Marg. Cost field values IS NOT equal to the

generator's marginal cost.

IC for OPF

Incremental cost of the generator at its current operating point.

Initial MW

The initial real power output of the generator at the beginning of the OPF solution. You can reset the case back to

these values by selecting the LP OPF, Restore Previous Control Settings menu item. This menu item is only

available following a successful OPF solution.

Initial Cost

The initial generator cost at the beginning of the OPF solution.

Delta MW

Change in the generator's real power output as a result of the OPF.

Delta Cost

Change in the generator's cost as a result of the OPF.

Min MW, Max MW

Minimum and maximum real power output of the generator.

Cost Model

The current cost model being used for the generator. The field value is either "Cubic", indicating that the

generator's operating costs are being modeled using a cubic cost function, or "Piecewise Linear", indicating the

operating costs are being modeled using a piecewise linear cost function. Toggle the field to change the model.

Note that a generator may simultaneously have a cubic model and a piecewise linear model.

Because the OPF uses a linear programming approach, the generator's operating costs are ALWAYS modeled

using the piecewise linear model. Generators with an existing cubic cost model are either 1) ignored as OPF

controls, or 2) have a piecewise linear cost model automatically created from the cubic model, depending upon the

values specified on the OPF Options dialog.

# Cost Curve Points

Shows the number of segments in the piecewise linear model. If no piecewise linear model exists then this field is

zero; the generator's costs are being modeled using the cubic function. For such generators you can automatically

setup a piecewise linear model simply by entering a non-zero value for the number of points. A piecewise linear

model is created that matches as closely as possible the existing cubic model.

Fuel Type

Specifies the fuel type of the generator, if it is known; double-click to toggle through the options. Options are

Unknown, Coal, Gas, Hydro, Hydro Pumped, Nuclear, Petroleum, Solar, Wind, and Other.

Profit $/hr

Shows the profit of the generator. Profit is calculated using this equation:

Profit = (GenMW * MW Marg Cost ) - [ FuelCost*( IOA + IOB * GenMW + IOC * GenMW ²+ IOD * GenMW ³ ) ]

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OPF Interface Records

Displays OPF specific information about the interface records in the case. To show select LP OPF > OPF Interface

Records. This display is actually a page of a display showing all the potential inequality constraints in the power

system. The top portion of the display repeats the fields shown on the Constraint Options page of the OPF Options

dialog.

To view the Interface records click on the Interfaces tab. This displays the interfaces page which is a class of Case

Information Display and therefore can be used in a manner consistent with the other case information displays.

Specific formatting options are available from the local menu, which can be accessed by right-clicking on any field in

the page. The columns can also be sorted by right-clicking on the heading of the field.

By default the Interface Records page contains the following fields:

Name

Name of the interface.

Monitor

Specifies whether or not the interface MW limit is enforced in the OPF solution.

Interface MW

The amount of MW flow on the interface.

MW Limit

The interface MW limit.

Percent

The amount of MW flow on the interface as a percentage of the limit.

Monitor Direction

The direction on the interface in which the flow is being monitored.

MW Marg. Cost $ / MWh

The marginal cost of enforcing the limit on the interface.

MW Unenforceable

This field will be set to YES if the interface limit is unenforceable in the OPF solution.

Constraint

This field will be set to YES if the interface limit is a constraint in the OPF solution.

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PowerWorld Simulator Add-on Tools

OPF Nomogram Records

This list displays OPF specific information about the nomogram records in the case. To show the list, select LP OPF >

OPF Nomograms. This display is actually a page of a display showing all the potential inequality constraints in the

power system. The top portion of the display repeats the fields shown on the Constraint Options page of the OPF

Options dialog.

To view the nomogram records click on the Nomogram Interfaces tab. This displays the nomogram interfaces page

which is a class of Case Information Display and therefore can be used in a manner consistent with the other case

information displays. Specific formatting options are available from the local menu, which can be accessed by right-

clicking on any field in the page. The columns can also be sorted by right-clicking on the heading of the field.

By default the Interface Records page contains the following fields:

Nomo. Name

Name of the nomogram.

Nomo. Seg.

The segment of the nomogram. Each segment of the nomogram is treated as a separate constraint in the OPF,

and therefore is listed individually in the OPF nomogram table.

Monitor

This field will be set to YES if the nomogram segment is monitored during the OPF.

Interface MW

The total MW flow for the segment of the nomogram.

MW Limit

The segment MW limit.

Percent

The amount of MW flow on the segment as a percentage of the segment’s limit.

Monitor Direction

The direction on the segment in which the flow is being monitored.

MW Marg. Cost $ / MWh

The marginal cost of enforcing the limit on the segment.

MW Unenforceable

This field will be set to YES if the nomogram segment’s limit is unenforceable in the OPF solution.

Constraint

This field will be set to YES if the nomogram segment’s limit is a constraint in the OPF solution.

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OPF Line/Transformer Records

Displays OPF specific information about the line and transformer records in the case. To show select LP OPF, OPF

Line/Transformer Records. This display is actually a page of a display showing all the potential inequality

constraints in the power system. The top portion of the display repeats the fields shown on the Constraint Options

page of the OPF Options dialog.

To view the Line and Transformer records click on the Line/Transformers tab. This displays the Line/Transformer

page which is a class of Case Information Display and therefore can be used in a manner consistent with the other

case information displays. Specific formatting options are available from the local menu, which can be accessed by

right-clicking on any field in the display. The columns can also be sorted by right-clicking on the heading of the field.

By default the display contains the following fields:

From Number, From Name, From Area Name

Number, Name, and Area Name of the From bus.

To Number, To Name, To Area Name

Number, Name, and Area Name of the To bus.

Circuit

Circuit identifier for the branch.

Monitor

Specifies whether or not the branch's MVA limit will be enforced in the OPF solution.

Max MVA

The maximum MVA flow on the branch. Value is determined based on the end of the branch with the higher MVA

flow.

% of MVA Limit (Max)

The maximum MVA flow as a percentage of the branch MVA limit. Value is determined based on the end of the

branch with the higher MVA flow.

Lim MVA

The MVA limit for the branch.

MVA Marg. Cost

The marginal cost of changing the MVA flow on the branch.

MVA Unenforceable

This field will be set to YES if the branch limit is unenforceable in the OPF solution.

Constraint

This field will be set to YES if the branch limit is a constraint in the OPF solution.

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OPF Load Records

Displays OPF specific information about each load record with a valid area/zone/owner filter. To show this display

select LP OPF > OPF Load Records. The OPF Load Records Display is a class of Case Information Display and

therefore can be used in a manner consistent with the other case information displays. Specific formatting options are

available from the local menu, which can be accessed by right-clicking on any field in the display. The columns can

also be sorted by right-clicking on the heading of the field.

By default the display contains the following fields

Number, Name

Number and name of the bus to which the load is attached. The display's local menu offers you the opportunity to

view the Quick Power Flow List and the Bus View Display for this bus. You can also use the local menu to view the

generator's dialog.

Alphanumeric ID used to distinguish multiple loads at the same bus.

Area Name of Load

Name of the load’s area.

AGC

Designates whether the load’s real power demand is governed by automatic generation control (AGC). If the AGC

field is set to Yes the load is on AGC in the standard power flow. When a load is on AGC its real power output is

varied automatically during an OPF or SCOPF solution ONLY, provided the load is part of an area or super area

that is also on OPF control. Loads will not be dispatched if the area is on some other form of AGC control.

In Simulator OPF the default operating mode is that only loads on AGC control are eligible to be OPF controls. In

addition, the load’s area or super area must have AGC Status of "OPF", and the area must have its Load MW

Dispatch set to YES.

The real power output of the load.

Cost Shift $/MWh, Cost Multiplier

The cost shift and cost multiplier allow you to easily apply a shift to the cost function for the purpose of assessing

how variations in bids impact profit. The cost function is affected based on the following equation:

(Original Cost Function + Cost Shift) * Cost Multiplier

Hourly Benefit

The total benefit of the load, including the impact of the cost shift and cost multiplier.

MW Marg. Cost

Tells the marginal cost, in $ / MWhr, to reduce one additional MW of load at this bus. If a load is available as a

control and is not at either its minimum or maximum limit or a cost model breakpoint, then the MW Marg. Cost field

will be identical to the load’s current marginal cost. However the usual case is for the load to be at either a limit or a

cost model breakpoint so the usual situation is that the MW Marg. Cost field value IS NOT equal to the load’s

marginal cost.

Inc. Benefit

Incremental benefit of the load at it’s current operating point.

Initial MW

The initial real power demand of the generator at the beginning of the OPF solution. You can reset the case back to

these values by selecting the LP OPF > Restore Previous Control Settings menu item. This menu item is only

available following a successful OPF solution.

Initial Cost

The initial load cost at the beginning of the OPF solution.

Delta MW

Change in the load's real power output as a result of the OPF.

Delta Cost

Change in the load's cost as a result of the OPF.

Min MW, Max MW

Minimum and maximum real power demand of the load.

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OPF Super Area Records

Displays OPF specific information about each super area record in the case. To show this display select LP OPF,

OPF Super Area Records. The OPF Super Area Records Display is a class of Case Information Display and

therefore can be used in a manner consistent with the other case information displays. Specific formatting options are

available from the local menu, which can be accessed by right-clicking on any field in the display. The columns can

also be sorted by right-clicking on the heading of the field.

By default the display contains the following fields:

Super Area

Alpha-numeric identifier of the super area.

AGC Status

Super area's automatic generation control status. This is the same field shown on the Super Area Records display.

The field indicates whether or not the super area's generation is changing automatically to control the super area's

interchange.

The super area AGC Status field always overrides the AGC Status for the individual areas, except when it is set to

"Off AGC".

To be included in the OPF this field MUST be "OPF". In that case the generation costs for all the areas in the super

area are included in the OPF objective function. Otherwise they are only included if the super area AGC Status is

"Off AGC" and their particular area's AGC Status is on "OPF". Double-click on the field to toggle its value.

Num Areas

Number of areas in the super area. To see the individual areas use the local menu to view the Super Area dialog.

Include Marg. Losses

Specifies whether or not to include marginal losses in OPF calculations for this super area.

MW Marg. Cost Ave.

If the super area is on "OPF" control then for a solved case this field shows the average of the bus MW marginal

costs for all the buses in the super area. If there is no congestion then all of the marginal costs should be equal.

MW Marg. Cost St. Dev.

Standard deviation of the bus MW marginal costs for the buses in the super area.

ACE MW

Area control error for the super area.

Gen MW, Load MW

Total real power generation and load in the super area.

Total Sched MW, Int MW

Scheduled and actual interchange real power interchange between the super area and the rest of the system. Both

of these fields are the algebraic summation of the scheduled and actual interchange for the areas in the super area.

Loss MW

Total real power losses for the super area.

MW Marg. Cost Min, MW Marg. Cost Max

Minimum and maximum of all the bus MW marginal costs for the buses in the super area.

Controls

OPF Controls

The following classes of controls are available during the OPF solution. Note, individual classes of controls can be

enabled/disabled for the entire case using the OPF Options dialog and for particular areas using the OPF Area

Records display. Also, all classes of controls have associated minimum/maximum limits which are always enforced.

Generator MW output

The generator MW outputs are the major control for controlling the MW flow in the network and for minimizing the

objective function. Only generators in areas or super areas that are on "OPF" control are eligible for control;

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otherwise the generator's MW output remains fixed at its initial value. Whether a particular generator is available for

control also depends upon the status of its AGC and OPF MW Control fields. These fields are set on the OPF

Generator Records display.

Phase shifting Transformer tap position

Phase shifting transformers are used primarily to control the flow of real power in the network. When phase shifting

transformers are controlled in the OPF routine, the phase angle is allowed to move anywhere within the phase

angle range of the device in order to help alleviate violations on other branches in the system. The flow on the

phase shifter is allowed to violate the prescribed MW range given for the phase shifter, but is NOT allowed to violate

the MVA rating of the device.

Additionally, in order for a phase shifter to be included in the OPF solution dispatch, the XF Phase property of the

area must be set to YES. Each individual phase shifter also has a property for being included in the OPF control

that must be turned on in order for the phase shifter to participate in the OPF dispatch. This option can be set for a

phase shifting transformer by opening its Information Dialog and checking the OPF Phase Shifter Control options on

the OPF page of the dialog.

Load MW Dispatch

The load MW demands can also be included as controls for re-dispatch during an OPF solution. The concept of

controlling a load is generally the same as controlling a generator. Loads can be assigned piecewise linear benefit

curves, and included in the OPF dispatch algorithm. Only areas whose AGC control is set to "OPF" are eligible for

control. Furthermore, the OPF area’s Load MW Dispatch property must also be set to YES. Each area load that is

to be included for OPF dispatch must have a benefit model defined, and have its Available for AGC field set to YES.

These fields can be set in the OPF Load Records display.

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OPF Phase Shifter Records

Displays OPF specific information about each phase shifter record in the case. To show this display, select LP OPF >

OPF Phase Shifter Records from the main menu. The OPF Phase Shifter Records display is a class of Case

Information Display and therefore can be used in a manner consistent with the other case information displays.

Specific formatting options are available from the local menu, which can be accessed by right-clicking on any field in

the display. The columns can also be sorted by right-clicking on the heading of the field.

By default the display contains the following fields:

From Number, From Name

The name and number of the bus at the From end of the phase shifter.

To Number, To Name

The name and number of the bus at the To end of the phase shifter.

Circuit

The circuit identifier for the phase shifter.

OPF Control

Specifies whether or not the phase shifter is available for control during an OPF solution.

Area PS Control

Specifies if automatic phase shifter control has been enabled for the area containing the particular phase shifting

transformer. If the area phase shifter control is disabled, all phase shifting transformers within the area will remain

fixed at their initial settings during the entirety of the OPF solution process. This setting overrides the individual

automatic control settings of each phase shifting transformer within the area.

XF Auto

Specifies if the transformer automatic control is enabled. If an individual transformer's automatic control is disabled,

it will remain at it's initial settings during the entirety of the OPF solution process.

Phase (Deg)

The actual phase shift of the phase shifter, in degrees.

Initial Degrees

The initial phase angle before the OPF solution was calculated.

Delta Degrees

The change in the phase angle during the OPF solution.

Tap Min, Tap Max

The minimum and maximum tap positions allowed for the phase shifter operation.

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Examples

OPF Example - Introduction

As a simple example of using the OPF, consider the seven bus, three area system contained in the file B7FLATOPF

(included with the PowerWorld Simulator). For this case all three areas are initially on Economic Dispatch (ED) AGC

control and hence by default would not be included in the OPF solution. Also, the initial interchange between the

areas is equal to zero and the generators are modeled using cubic cost functions.

To initially solve the case using the standard power flow, select Single Solution. The case should look like the first

figure below.

Now we'll modify the case to set the three areas for OPF control. To do this, select LP OPF > OPF Area Records to

display the OPF Area Records display. Toggle the AGC status for each of the three areas to change it to "OPF". Now

select LP OPF > Primal LP to solve the case using the LP OPF. The results should look similar to the second figure

below. The one-line shows the hourly cost for each area and the total case hourly cost, equal to $ 16,883 / hr.

Note that the results are very similar but not identical to the economic dispatch case. We would expect the cases to

be similar since for cases with no conges tion the OPF solution should be (ideally) equal to the economic dispatch

solution. The difference between the two is because in the LP OPF the generator cost functions are converted from a

cubic model to a piece-wise linear model using a user specified number of segments, which is 5 segments by default.

This value can be viewed/modified from General Options page of the OPF Options display.

Change the Total Points Per Cost Curve field to 100 and resolve. The results are shown in the third figure below,

which now are almost identical to the economic dispatch results. The disadvantage though in using a large number of

cost segments is that it degrades the performance of the LP OPF slightly on larger cases.

B7OPF Case Solved using Economic Dispatch

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OPF Example - Super Areas

To jointly dispatch the three areas we'll first combine them into a single super area. To setup the super area first

select LP OPF > OPF Super Area Records to display the OPF Super Area Records display (alternatively you could

also use the Case Information > Super Area display). To enter a new super area right click on the "None Defined"

entry in the first row of the display to show the display's local menu. Select Insert. This displays the super area dialog

. In the Name field enter a name for the new super area, "ThreeAreas." Then select the Add New button to create a

new super area. To add the three areas to the new super area enter "1-3" in the New Area #'s field and then select

Add New Areas by Number (alternatively you could select the areas from the New Area Name list). Also, to enable

the super area for control, set the Super Area Control Options field (AGC Status) to Optimal Power Flow (OPF.)

Before resolving the OPF lets temporarily disable enforcement of line MVA constraints. You can do this from the

Constraint Options page of the OPF Options dialog. Check the Disable Line/Transformer MVA Limit Enforcement.

Also, now would be a good time to save the changes. To avoid overwriting the existing B7OPF file, select File > Save

Case As to save the case (pwb and pwd f iles) with a different name, say B7OPFSA (SA for super area).

Select LP OPF > Primal LP to resolve the OPF. The results should be as shown below.

OPF Solution with Super Area WITHOUT Enforcing Line MVA Constraints

With the super area the individual area interchange constraints are no longer enforced. This permits the free

interchange of power between the areas, resulting in an overall decrease in the total case hourly cost from $ 16,885 /

hr to $ 16,251 / hr. View the OPF Bus Records display to v erify that all the bus marginal costs are identical, equal to $

17.10 / MWh. Of course the key problem with solving the system using the super area is that now there are line

violations. These violations will be removed next by enforcing the line MVA constraints.

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OPF Example - Enforcing Line MVA Constraints

To remove the line MVA violations go back to the Constraint Options Page of the LP OPF > OPF Options Dialog.

Uncheck the Disable Line/Transformer MVA Limit Enforcement.

Now resolve the LP OPF, enforcing the line constraints. The resultant solution is shown below.

OPF Solution with Super Area WITH Line MVA Constraint Enforcement

With line constraint enforcement active the OPF optimally redispatches the generation taking into account the line

MVA limits. However enforcing these line constraints comes at a cost. Notice that the total case hourly cost has

increased from $ 16,251 / hr to $ 16,553 / hr, which is still substantially less than the $ 16,885 / hr figure we had for the

case without the superarea.

Enforcing the line constraints also has an impact on the bus marginal costs, shown below.

Impact of Line MVA Enforcement on the Bus Marginal Costs

The actual marginal cost of enforcing the line constraint can also be viewed on the LPOPF, OPF Line/Transformer

MVA Records display. The MVA Marg. Cost tells the marginal cost of enforcing the constraint, expressed in units of $

/ MVA / hr. Right-click on the MVA Marg Cost field header to sort the display using this field.

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Store LP OPF Data

Select LP OPF > Store LP OPF Data to store LP OPF specific fields from the case into the specified *.pwo text file.

Note, the LP OPF specific fields are saved with the case in the pwb file. The pwo files should therefore only be used

for transferring the opf specific data between cases or f or the user to manually change the data using a text editor.

Data can be loaded into a case from the *.pwo text file using the LP OPF > Load LP OPF Data menu command.

Security Constrained Optimal Power Flow (SCOPF)

Security Constrained Optimal Power Flow Overview

Note: The SCOPF option in PowerWorld Simulator is only available if you have purchased the SCOPF and

OPF add-ons to the base package. To learn more about the SCOPF, please feel free to read through the

information contained in these help files. Contact PowerWorld Corporation for details about ordering the

SCOPF and OPF versions of Simulator.

The optimal power flow (OPF) algorithm has the purpose of minimizing an objective function (usually total operation

cost) by changing different system controls while meeting power balance constraints and enforcing base case

operating limits. The secure operation of a power system though requires that there be no unmanageable contingency

violations, either. Thus, the minimization of the objective function requires considering contingencies. This is

achieved using a security constrained optimal power flow (SCOPF) algorithm.

During the SCOPF solution process the algorithm determines the optimal state of the system by iterating between

solving a standard power flow and solving a linear program that changes the system controls to remove contingency

violations.

The SCOPF algorithm makes control adjustments to the base case (pre-contingency condition) to prevent violations in

the post-contingency conditions. If enough controls are available in the system, the solution minimizes the objective

function and the system enforces contingency violations. If the system does not have enough controls, then some

violations may be persistent under certain contingencies. Those represent unenforceable constraints, which result in

high bus marginal costs.

The commands and options for the SCOPF are accessed using the LP OPF > Security Constrained OPF option.

The SCOPF function uses the OPF options defined in the OPF Options dialog and the contingency settings specified

in the contingency analysis dialog. Please read through the OPF and the contingency analysis help for more

information about these settings. We encourage you to become familiar with Simulator OPF and the contingency

analysis tool before running SCOPF simulations. Other commands in the SCOPF dialog are used to specify the base

case solution process and for accessing the SCOPF results.

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SCOPF Solution Process

The SCOPF involves three major steps that can be solved either automatically or manually from the SCOPF control

dialog:

· Initialization to setup the SCOPF LP tableau and the control structures

· Contingency analysis calculation and storage of control sensitivities associated with each contingency violation

· SCOPF iterations, which include an LP solution and a power flow solution. During each LP step in the LP

routine, the algorithm enforces the newest most severe contingency violation. After each violation is processed,

all of the unprocessed violations are updated. This step is crucial since often resolving the most severe violation

resolves numerous other violations. For instance, a single line might be overloaded in a number of

contingencies: fixing the worst contingency fixes the others as well. On the other hand, processing some

violations may result in new violations. Currently SCOPF does not check for new violations, which would require

a new contingency analysis solution. Care must be taken during the outer loop since the corrected violations will

no longer show up as binding and hence will be excluded from the SCOPF LP tableau. The contingency

violations are listed in the CTG Violations dialog.

The SCOPF terminates when all the contingency violations have been processed. Note that the user can rerun the

SCOPF by repeating the solution process if they want to verify the contingency violation enforcement at the new

optimal operating point.

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SCOPF Equality and Inequality Constraints

Two general types of constraints are involved in the SCOPF solution: equality and inequality constraints. Equality

constraints are constraints that have to be enforced. That is, they are always "binding". For example in the SCOPF,

as well as in the OPF and in the power flow, the real and reactive power balance equations at system buses must

always be satisfied (at least to within a user specified tolerance). In contrast, inequality constraints may or may not be

binding. For example, a line MVA flow under a certain contingency may or may not be at its limit.

The SCOPF problem is solved by iterating between a power flow solution and a contingency constrained LP solution,

some of the constraints are enforced during the power flow solution and some constraints are enforced during the LP

solution. The constraints enforced during the power flow are, for the most part, the constraints that are enforced

during any power flow solution. These include the bus power balance equations, the generator voltage set point

constraints, and the reactive power limits on the generators. What differentiates the SCOPF from a standard power

flow and from the OPF are the constraints that are explicitly enforced by the LP solver. These include the following

constraints:

Equality Constraints

Inequality Constraints

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SCOPF Inequality Constraints

The following classes of inequality constraints are enforced during the SCOPF solution.

Generator real power limits

Generator real power limits are enforced during the SCOPF LP solution.

Generator reactive power limits

Generator reactive power limits are enforced during the SCOPF LP solution.

Interface MW Limits

Interface MW limits are enforced during the SCOPF solution. Interfaces are used to represent the aggregate flow

through a number of different devices. During the SCOPF the MW post-contingency flow through the interface is

constrained to be less than or equal to a user specified percentage of its limit, provided the interface is active for

enforcement. For an interface to be active for enforcement the following three conditions must be met:

· Interface enforcement must not be disabled for the case. This field can be set from either the OPF

constraintsOPF_Options_Constraint_Options dialog or the OPF interfacesOPF_Interface_Records info display.

As default, the interface enforcement is not disabled. Note that interface flow is limited to a percent of its limit as

specified by the interface's Limit Monitoring SettingsLimit_Monitoring_Settings.

· Interface enforcement must be active for at least one of the interface's areas. Note, an interface is assumed to

be in each area that contains at least one of its components. This field can be set from the OPF Area

RecordsOPF_Area_Records display. Note: the default is that interface enforcement is not active, so be sure to

activate this if you want these cons traints enforced.

· Enforcement must be active for each individual interface. This field can be specified from the OPF Interface

RecordsOPF_Interface_Records display or in the Limit Monitoring SettingsLimit_Monitoring_Settings dialog.

The default is active.

Each interface that is active for enforcement is modeled as an inequality constraint, which may be either binding or

not binding. If the constraint is not binding then it does not impact the solution. If a constraint is binding then it has

an associated marginal cost of contingency enforcement. When manually solving the SCOPF one can skip a

contingency violation associated to the interface by setting the Include field of the SCOPF CTG Violations dialog to

No.

Transmission Line and Transformer (Branch) MVA Limits

Transmission line and transformer (branch) MVA limits are enforced during the SCOPF solution. During the LP the

post-contingency branch line flow is constrained to be less than or equal to a user specified percentage of its limit,

provided the branch is active for enforcement. For a branch to be active for enforcement the following three

conditions must be met:

· Line/Transformer enforcement must not be disabled for the case. This field can be set from either the OPF

constraints dialogOPF_Options_Constraint_Options or the OPF Line/Transformer

RecordsOPF_Line_Transformer_Records display. The default is that case line/transformer enforcement is not

disabled. Also note that the branch flow is limited to a percent of its limit as specified by the branch's Limit

Monitoring SettingsLimit_Monitoring_Settings.

· Branch enforcement must be active for the branch's area. Enforcement For tie-lines must be active for either

area. This field can be set from the OPF Line/Transformer RecordsOPF_Line_Transformer_Records display.

The default is that branch enforcement is not active, so be sure to activate this if you want these constraints

enforced.

· Enforcement must be active for each individual branch. This field can be set from the OPF Line/Transformer

Records display or in the Limit Monitoring Settings Dialog. The default is active.

Each branch that is active for enforcement is modeled as an inequality constraint, which may be either binding or

not binding under contingency conditions. If the constraint is not binding then it does not impact the solution. If a

constraint is binding then it has an associated marginal cost of enforcing the contingency constraint, which is shown

on the SCOPF Bus Marginal Price Details dialog. When manually solving the SCOPF one can skip a contingency

violation associated to the branch by setting the Include field of the SCOPF CTG Violations dialog to No.

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SCOPF Control

The control dialog allows the user to manually or automatically run a SCOPF simulation and visualize the execution of

the simulation. The SCOPF solution process involves three steps: base case solution and initialization, contingency

analysis, and SCOPF iterations.

Run Full Security Constrained OPF

Press this button to run the three steps of the SCOPF solution automatically. The SCOPF will solve the base case

using the selected method, will use the currently stored list of contingencies during the contingency analysis step,

and will take the CA results and sensitivities to iterate in order to obtain the optimal solution that minimizes cost and

enforces contingency violations.

Options

Maximum Number of Outer Loop Iterations

Indicates the number of maximum outer loop iterations. The outer loop iterations determines how many times the

contingency analysis will be re-run following a successful SCOPF dispatch. In this manner, Simulator will look for

new violations that may occur due to the new generation dispatch. The original violations considered will not be

considered again, only new violations will be examined. The presumption is that the original violations will not

resurface. Resolving the contingency analysis independent of the SCOPF routine after the SCOPF dispatch is

acquired will indicate if any earlier violations resurfaced from the final iterated SCOPF dispatch.

Consider Binding Contingent Violations from Last SCOPF Solution

When checked, this option ensures that the contingent violations from the last SCOPF solution are included in the

current SCOPF solution. This option is helpful in preventing the SCOPF from hunting between having a constraint

binding in one solution, and resolving with it not binding in a later solution because it was previously remedied. This

option should generally always be checked, unless the user is sure that the previous solution has no bearing on the

current solution, such as having made major changes to the system since the previous solution.

Initialize SCOPF with Previously Binding Constraints

When checked, this option results in the SCOPF solution process starts with the exact same LP tableau from the

last solution. This can make for fairly fast solutions (recognizing that the contingency analysis needs to be

resolved) when the changes to the system are small. Simulator automatically uses this option when doing multiple

outer loops of the SCOPF. This option allows the user to solve the outer loops (set the outer loop counter to 1) by

repeatedly solving the SCOPF manually, potentially making modifications between solutions if desired.

Set Solution as Contingency Analysis Reference Case

Check this field to set the solution of the SCOPF as the contingency analysis reference. If the system has enough

controls to remove all the contingency violations, a rerun of the contingency analysis using the SCOPF solution as

the reference should report no branch violations.

Maximum Number of Contingency Violations Allow Per Element

Specify the maximum number of contingency v iolations that the SCOPF analysis should allow per element.

Basecase Solution Method

Specifies whether the solution of the base case is performed using the power flow algorithm or the optimal power

flow algorithm. The selection will affect the initial conditions of the system and consequently the contingency

analysis results and the sensitivities used by the LP solver. Currently the SCOPF does not resolve the contingency

analysis during the optimization since this is computationally expensive. See the SCOPF solution process for

details.

Handling of Contingent Violations Due to Radial Load

It is often common when computing a security constrained OPF to have violations occur on branches due to radial

load. In these instances, there is no way to adjust c ontrols to continue to serve the load, without overloading the

serving element. Therefore you can choose how contingent violations of this type should be handled by the

SCOPF. You can choose to flag them but not include them in the SCOPF, ignore them completely, or include the

violations in the SCOPF. Note that if you include the violations in the SCOPF, the SCOPF algorithm will not be able

to remove the violation on the element via generation dispatch. However, it may be able to do so if the load in

question has a load benefit curve defined and is available for load shed dispatch in the SCOPF routine.

DC SCOPF Options

The DC options given for the SCOPF revolve around the treatment of Line Outage Distribution Factors (LODF)

during the DC SCOPF solution. You can choose to discard the LODFs when the SCOPF is finished, store them in

memory (lost when Simulator is closed,) or in memory and in the PWB file (if saved.)

If the LODFs have been stored and you wish to clear them (they can require quite a bit of RA M depending on the

number of contingencies and size of the case,) you can press the button labeled Clear Stored Contingency

Analysis LODFs .

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Number of Outer Loop Iterations

The number of outer loop iterations required to solve the SCOPF.

Number of Contingent Violations

Number of violations from the contingency analysis portion of the solution, which are used to attempt to determine

the security constrained dispatch.

SCOPF Start Time, SCOPF End Time

Physical time when the SCOPF solution process started and finished.

Total Solution Time (Seconds)

Length of time needed to determine the SCOPF solution.

Total LP Iterations

Total number of Linear Programming iterations necessary to determine the SCOPF solution.

Number of Active Contingencies

Is the number of contingencies included in the SCOPF simulation Specific contingencies may be excluded from the

simulation in the contingency analysis dialog by changing the skip field of a contingency to YES. The contingency

analysis dialog can be conveniently accessed from the SCOPF control dialog.

View Contingency Analysis Form

Clicking this button shows the contingency analysis dialog.

Contingency Analysis Results

This window allows the user to monitor the details of the contingency analysis step. During contingencies, the

outage actions, the solution of each contingency, and the solution of the CA run are reported.

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SCOPF CTG Violations

The contingency violations page is available from the Results tab of the Security Constrained Optimal Power Flow

form. The display lists the results from the latest contingency analysis run including the violations that were included

in the SCOPF and the final error for each violation. This dialog may change if the user reruns the SCOPF by solving

the contingency analysis using the SCOPF solution as contingency analysis reference. 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 shows the following fields:

Contingency Name

This is the contingency label. By default single line contingencies start with an "L", single generator outages with a

"G", and single transformer outages start with an "X".

PowerWorld Simulator version 11. Manual - page 18