Contingency Element Type: Interface

See Also

The following describes the options available when creating a contingency element of type Interface. Contingency elements are created from the Contingency Element Dialog, and additional details of how to create contingency elements can be found here.

Action Settings

Open

The Open action will set the Status of all ac branches in the selected interface to Open. If all of the ac branches are already open, then this action does nothing. The Status of any dc lines that are part of the interface will remain unchanged due to the contingency action. If the selected interface contains additional interfaces, the Status of all ac branches in the additional interfaces will also be set to Open.

Added in version 19, build on November 21, 2016

In addition to all ac branches being opened, all generators and loads will have their Status set to Open . This includes generators and loads in injection groups and any generators and loads contained in other interfaces contained by the interface being opened.

Open Breakers

See the special topic on Open Breakers for more detail.

The Close action will set the Status of all ac branches in the selected interface to Closed. If all of the ac branches are already closed, then this action does nothing. The Status of any dc lines, generators, loads, or injection groups that are part of the interface will remain unchanged due to the contingency action. If the selected interface contains additional interfaces, the Status of all ac branches in the additional interfaces will also be set to Closed.

Close Breakers

See the Close Breakers for Contingencies topic on the Contingency Element Dialog topic.

Set To Added in version 19, build on May 3, 2016

The Set To action will set the real power flow on the interface to the specified Amountby opening devices in the interface. The real power flow can be set in Percent or MW. When setting the flow in Percent, the flow is set to the specified percent of the contingency reference state real power flow. When setting the flow in MW, the real power flow is set to the specified amount. The treatment of interfaces within interfaces will be to open the entire contained interface.

Scale Order

This option determines how the devices within the interface will be opened to implement the desired action. The following choices are available:

Merit Order Open

Each element within an interface has a Par Fac field that specifies the merit order in which the flow will be adjusted by opening elements. Each element is opened in the order of highest to lowest Par Fac until the desired flow is met. If opening an element will cause a change in flow that is not in the desired direction, that element is not opened and the next element in merit order is examined. The flow of an element is determined by its MW flow multiplied by the Weighting factor specified with the element. See the Specifying Participation Factors for Interfaces section below for more information on how to specify these.

Depending on the mix of elements included within the interface, the Weighting should be used to determine the correct direction of flow for an element. As an example, the flow for a load will be negative because it is a negative injection into the system. If using an interface that includes branches as proxies for multiple loads in addition to some single loads, the loads in the interface should use a Weighting of -1 to get a positive flow value. The branches used as proxies for multiple loads should be specified in the direction of positive flow so that the total flow on the interface is positive. The desired Amount can then be specified relative to this positive flow.

There are two options that determine how the opening of elements is done:

Do Not Exceed Amount - This will open elements until the amount of MW opened is as close to the desired amount as possible but has not exceeded the desired amount. If opening an element will cause the amount of MW opened to exceed the desired amount, that element will be skipped and the next one in merit order will be examined.

Allow to Exceed Amount - This will open elements until the amount of MW opened is equal to or greater than the desired amount.

Best Fit Open Added in version 20

When using this option the participation factors of interface elements do not impact which elements are opened. The flow on an element, which is determined by its MW flow multiplied by the Weighting factor specified with the element, is used to determine which elements should be opened. If the flow on an element is in the appropriate direction to achieve the desired flow change on the interface, that element is eligible for being opened.

To determine if an element will actually be opened, the best fit algorithm attempts to determine the combination of elements that will achieve the desired flow change by opening the least amount of elements and achieving an actual flow change within 5% of the desired flow change. If Allow to Exceed Amount is used, the action will attempt to achieve a flow change that is above the desired change, but within 5%. If Do Not Exceed Amount is used, the action will attempt to achieve a flow change that is below the desired change, but within 5%.

Modified in version 22, build on May 26, 2021

The algorithm attempts to find the smallest number of devices that can meet the desired amount. The more devices there are to consider the more time it takes to determine all of the possible combinations. If there are more than 20 devices (2^20 = 1,048,572 combinations), the devices will be sorted from high to low impact and examined in blocks of 20. If the entire 20 devices are needed to meet the desired amount all will be opened and then the next block of 20 devices will be used to meet the remaining amount. This process continues until it is not necessary that a set of 20 devices are all required to meet the remaining amount. This block will use the combination algorithm to fine tune which devices are opened.

Change By Added in version 19, build on May 3, 2016

The Change By action will change the real power flow in the interface by the specified Amount. The real power flow can be changed in Percent, MW, or MW Effect. When changing the flow in Percent, the flow is changed by the specified percent of the contingency reference state real power flow. When changing the flow in MW, the real power flow is changed by the specified amount. The treatment of interfaces within interfaces will be to open the entire contained interface.

Added in version 20

When choosing the MW Effect option, the Scale Order option Best Fit Open is automatically checked. The value that is specified with the action will be the desired MW Effect that the action should have. The participation factors, Par Fac field, defined with the interface elements will be interpreted as effectiveness factors akin to transfer distribution factors. These factors are supplied as input by the user when defining the interface. The effectiveness factors are multiplied by the present MW flow of elements in the interface to determine how much effect they will have if dropped. The flow of an element is determined by its MW flow multiplied by the Weighting factor specified with the element. If the effect of a particular element is in the opposite direction of the desired effect, that element is skipped. The action will find the smallest number of elements to drop that results in a total MW Effect that is within 5% of the desired MW Effect. If the option is picked to Allow to Exceed Amount then the action will attempt to achieve a MW effect that is above the value specified, but within 5%. If the option is picked to Do Not Exceed Amount, then the action will attempt to achieve a MW effect that is below the value specified, but within 5%.

Scale Order

This option determines how the devices within the interface will be opened to implement the desired action. The following choices are available:

Merit Order Open

Same as Set To section.

Best Fit Open Added in Version 20

Same as Set To section for changing in MW or Percent. This option can also be used with MW Effect changes as described above.

Evaluate Part Points in Reference State Added in version 19, build on May 3, 2016

When using an action that requires participation factors, this option can be used to indicate that participation factors should be determined in the contingency reference state.

Specifying Participation Factors for Interfaces Added in version 19, build on May 3, 2016

When using an action that requires participation factors, the participation factors can be set through the Interface Display using the Par Fac field. The Par Fac can be specified as a floating point value, a field associated with the interface element, or a Model Expression. To specify a field, the following syntax should be used: <Field>variablename. To specify a Model Expression, the following syntax should be used: <Expression>ModelExpressionName. When using either a field or model expression, checking the Evaluate Part Points in Reference State option will use the value determined in the contingency reference state, otherwise the present value will be used.