Breaker Isolated Groups

 

Breaker Isolated Groups are groupings of buses that are bounded by any combination of explicit breakers, implicit breakers, and open branches. These groupings can be accessed on a standalone dialog or used to auto-insert contingencies. The following describes how the groupings are identified and how they can be used.

 

Determining Breaker Isolated Groups

Breaker isolated groups are groupings of buses that are bounded by any combination of explicit breakers, implicit breakers, and open branches. The boundary branches are defined as follows:

 

Explicit Breakers

These are branches that have BranchDeviceType = Breaker.

Implicit Breakers

Each bus record has an Implicit Breakers field that can be found in the Topology folder in the list of available fields. This field is used to indicate where breakers are located when explicit breakers have not been modeled. If Implicit Breakers = YES for a bus, it is assumed that any device connected to that bus will have a breaker in series with it. For a branch that is connected to an implicit breaker bus, the algorithm to identify bus groupings will behave as though that branch itself is a breaker.

Open Branches

When based on the current system state an open branch is one where Status = Open. The normal status of branches can also be used. When determining the groupings either through the dialog or when auto-inserting contingencies, there is an option to Use Branch Normal Status for Groupings. When this option is used, an open branch is one where Normal Status = Open.

 

To determine the groupings, the connections to a bus that has not already been examined are traversed. Buses are accumulated into a new group until there are no remaining connections to unexamined buses that can be traversed from the starting bus. Boundary branches are found when an explicit breaker, implicit breaker bus, or open branch is encountered. These are the boundaries that connect one bus group to another. The boundary branch when an implicit breaker bus is encountered is the branch with one terminal bus in the current group and the other terminal bus defined as having implicit breakers. DC line connections are assumed to have breakers and these are not traversed. This process is repeated until all buses in the case have been examined.

Groupings are identified by assigning a Breaker Group Number to each bus with the groupings formed by buses with the same number.

 

Breaker Isolated Groups Dialog

The Breaker Isolated Groups dialog can be found on the Tools ribbon tab in the Other Tools ribbon group under Connections > Breaker Isolated Groups.

Breaker Isolated Groups are defined as described in the Determining Breaker Isolated Groups section. The dialog contains tabs for showing groupings based on bus, generator, load, switched shunt, and branch. Regardless of object type, the groupings are always determined by bus and an object's terminal bus or buses will determine its group.

Checking the Use Branch Normal Status for Groupings option will consider open branches to be those where Normal Status = Open. If this option is not used, open branches are those where Status = Open.

Click the Find Isolated Groups button to determine the groupings and populate the Breaker Group Number field.

The Filter Display Below By Range box takes an integer range list that can be used to filter the list of devices by Breaker Group Number. Click the Update Filter button to update the filtering after specifying the group numbers by which to filter.

 

Auto Inserting Contingencies by Breaker Isolated Groups

On the Auto Insertion of Contingency Records dialog the Bus grouping option will use breaker isolated groups of buses to create new contingencies. When auto-inserting contingencies, the same methodology as described in the Determining Breaker Isolated Groups section is used for determining the breaker isolated bus groupings as when displaying the groupings in the dialog, but not all groupings will result in contingencies being created.

The boundary branches and other devices (lines, transformers, series capacitors, generators, and loads) internal to bus groups are used for defining contingency actions and naming contingencies. Here are the different naming conventions and included contingency actions based on the type of boundary branches. Additionally, contingencies will not be created for some groupings.

 

At Least One Implicit Breaker

• The boundary branches are the result of at least one implicit breaker
  • Contingency element actions are the boundary branches defined as OPEN actions
  • Contingency is named based on the concatenation of bus numbers and names of the buses at the boundaries of the bus group (buses on the outside of the group) used to form the contingency
  • Open branches are included as actions in the contingency, but their boundary buses will not be used in the naming of the contingency
  • If a bus group contains generators or loads at internal buses, the generators and loads will be included as OPEN actions
  • Generators and loads at implicit breaker buses are not included as actions in the contingency
• For purposes of creating contingencies, branches that connect two buses defined with implicit breakers can form their own grouping
  • These groupings have a single line and no buses
  • Element action is defined as an OPEN on the single branch in the group
  • The contingencies are named for the single branch in the group

All Explicit Breakers

• The boundary branches are all explicit breakers with no implicit breakers
  • Contingency element action is OPEN WITH BREAKERS for the internal group device with the highest priority
  • Internal device priority is branch (line, transformer, or series capacitor) with the largest absolute reactance, generator with the largest MW Max, and load with the largest MW output
  • Contingency is named for the internal device with the highest priority that is also selected as the device for the contingency action

At Least One Explicit Breaker and No Implicit Breakers

• The boundary branches are a combination of explicit breakers and open branches that are not explicit breakers with no implicit breakers
  • Contingency element actions are the boundary branches defined as OPEN action
  • Contingency is named for the internal group device with the highest priority
  • Internal device priority is branch (line, transformer, or series capacitor) with the largest absolute reactance, generator with the largest MW Max, and load with the largest MW output

Contingencies Not Created

• Groupings that have more than 20 generators. This is to prevent creating a contingency for most of the system when dealing with a case that only has implicit or explicit breakers in part of the system.
• Separate generator or load contingencies for generators and loads that are attached to implicit breaker buses
• Open branches are treated as boundary branches for finding the groupings. No contingency will be created if all boundary branches are open.
• Groupings created by all explicit breakers for which there are no internal group devices
• Groupings created by boundary branches with at least one explicit breaker and no implicit breakers for which there are no internal group devices