See AlsoThe contingency action type Open Breakers is available for each contingency element type for which the Open action type is available. This includes the following element types: Branch, Bus, Load, Generator, Switched Shunt, DC Line, Injection Group, Interface, and Substation. This action type is only available for contingency records and is not available for contingency block definitions or for global contingency actions.
In order to handle the Open Breakers contingency elements, before one contingency's solution is performed, the list of contingency elements for that contingency is processed by looking for elements that use Open Breakers. For elements with this action type, all of the terminal buses of the respective device are processed using the algorithm below to determine which breakers to open to isolate the device (and possibly which generators to outage). The basic idea of the algorithm is to search for a list of breakers that will isolate all of the terminal buses of the device from in-service generation. The algorithm will also return a list of online generators that must be opened to isolate the bus as well. Remember that a breaker is specified by setting the Branch Device Type to Breaker.
Using the list of breakers and generators found from the algorithm, contingency analysis augments the contingency element list with a dynamically created list of contingency elements of action type Open for each breaker and generator device. The dynamically created elements are given the same Model Criteria and Status as the contingency element that required their creation. If multiple Open Breakers contingency elements require the same breaker to open, one new contingency element will be created. When Open Breakers contingency elements have different Model Criteria, a new contingency element will be created for each unique Model Criteria. During the actual contingency solution, the What Actually Occurred list will be updated and can be examined in the results to determine what breakers were needed to isolate the device. Finally, after the contingency solution is completed, all of the dynamically created contingency elements are deleted, and as a result, the user can only see which breakers or generators were opened by looking at the What Actually Occurred list.
For brevity in the context of tools that either automatically switch or identify breakers to open a device, the term breaker is used to indicate any type of device that can be switched automatically. For contingency analysis, only Branch Device Types of Breaker will be switched, and Disconnects are not included. Other tools may allow different branch device types or user options to specify the branch device types. If the model has no branches defined with the specified branch device types, this option will not work because the algorithm will never find any breakers. See the Full Topology Model topic for more information on defining breakers.
Algorithm Description for Open with Breakers During Contingency Analysis
The general algorithm for determining the breakers to open applies during contingency analysis. There are a few exceptions during contingency analysis as noted below:
- If there is another contingency action inside this same contingency that specifies an action type of Open or OpenCBs for a generator device, encountering that generator won't count toward the list of generators to open or the maximum of 10 buses to encounter with online generation. The same is done for any generator connected to a bus or inside an injection group, if the bus or injection group has a contingency action of type Open or OpenCBs.
- If there is a contingency action inside this same contingency that specifies a breaker with action type Open Breakers, the algorithm will traverse across this breaker (this models a breaker failure where a breaker is supposed to open but fails to operate.)
- If there is a contingency action inside this same contingency which specifies an action type of Open for a branch or DC line device, the algorithm will NOT traverse across that branch or DC line. The same is done for any branch which is part of a three-winding transformer, interface, or connected to a bus of the three-winding transformer, interface, or bus has a contingency action of type Open.
- While a list of generators to open is maintained, if no online load is encountered while traversing buses in the algorithm, then the generator OPEN contingency actions will not be created. This is because the breakers will create an isolated island with no load and thus opening the generation is not necessary.