Equivalents Display
See Also
The Equivalents Display is used to construct equivalent systems. An Equivalent System is a system of smaller dimension that exhibits similar power flow properties. Equivalent systems are constructed to help accelerate computation time without sacrificing a significant amount of accuracy. For more information, please see Equivalents.
To bring up the Equivalents Display, while in Edit Mode, go to the Tools ribbon tab, and choose Equivalencing... from the Edit Mode ribbon group. This display contains two pages, the Select The Buses Pageand the Create The Equivalent Page. Use the Bus Selection Page to partition the power system into the study system and the external system. Use the Create Equivalent Page to
- Save the external system in a file
- Extract the external system
- Build an Equivalent
Each of these tasks is described below.
Select The Buses Page
To perform any of the tasks described on the Create Equivalent Page, you first need to specify the study system and the external system. Do this by directly assigning buses to the desired system. The Select The Buses Page has been designed to provide a number of powerful and complimentary ways of accomplishing this task.
The most important point to keep in mind when using this page is that membership in the study system and the external system is on a bus-by-bus basis (as opposed to by areas or zones). Thus, each bus is either in the study system or the equivalent system. Each bus’ current assignment is indicated in the Buses list, which is shown on the bottom left corner of the page. The Buses list is a Case Information display and can be manipulated similar to other displays. By default, all buses initially reside in the study system. Please see Select The Buses Page for more details.
Create The Equivalent Page
The Create Equivalent Page allows you to save the external system in a file, to delete the external system, and to build the power system equivalent.
Build Equivalent
This procedure constructs an equivalent system. For background on equivalents, please see Equivalents. The following sections contain the options for building an equivalent.
Delete All External Generators or Retain Generators with Max MW Ratings Above
Retain Remotely Regulated Buses
Some generators and transformers regulate buses other than their terminals. When this box is checked, these remotely regulated buses are automatically included in the equivalent if the regulating generator or transformer is included. If the box is not checked, the regulated bus is set to the terminal of the retained object. It is strongly recommended that you leave this box checked at all times.
Retain Branch Terminals For
This section allows you to customize the retention of branch terminals for special-case types of branches. You may choose to retain terminal buses for transformers, zero impedance ties, area tie lines, and/or zone tie lines.
Max Per Unit Impedance for Equivalent Lines
During the equivalencing process, a number of equivalent lines are created joining the boundary buses. All equivalent lines with per unit impedance values above this threshold are ignored.
Two Character Circuit ID for New Equivalent Lines
Choose the circuit identifier to be used for the equivalent lines that are created. Choose between 97, 98, 99 or EQ for circuit IDs of equivalent lines.
Remove External Objects from Onelines
This feature removes display objects associated with the external system from any open onelines.
Convert Equivalent Shunts to PQ Loads
During the equivalencing process, shunt elements are added at the boundary buses. Check this box if you would like these equivalent shunts converted to constant PQ loads. If this option is checked, equivalent loads are created with a load ID of 99.
Remove Radial Systems
Checking this option results in all radial connections in the network to be reduced to their nearest non-radial bus (i.e. node.) The equivalencing routine will iteratively reduce the network when this option is checked, until no more radial connections exist in the system.
Delete Empty Areas/Zones/Substations that occur from Equivalencing
Since equivalencing is a process which ultimately removes buses from the system, and Areas, Zones and Substations are system devices which are groups of buses, this option will automatically remove the definition of these types of objects when all buses within them are removed from the case during the creation of the equivalent.
Adjust Area Unspecified Interchange to Zero Out ACE
Selecting this option will allow Simulator to automatically change the unspecified MW interchange amounts of each area to remove any non-zero ACE discrepancies caused by the equivalencing. This will help prevent these discrepancies from being assigned to the system slack bus.
Include Generator Dynamic Equivalents
Selecting this option will allow Simulator to automatically create dynamic equivalents of generators.
Minimum PU H for New Equivalent Generators
During the equivalencing process, a number of equivalent generators are created. All equivalent generators with per unit impedance values below this threshold are ignored.
Two Character Circuit ID for New Equivalent Generators
Enter the circuit identifier to be used for the equivalent generators that are created. Default is EQ.
Select Build Equivalent System to construct the equivalent system. Constructing an equivalent system permanently removes the external system from the case and adds a number of equivalent lines and shunts/loads.
Saving the External System in a File
This procedure allows an external system to be saved in a file without deleting the external system. This option is useful for allowing you to save a portion of the system in a file, modify it using perhaps another program, and then use Append Case to append the modified file to the original case.
When saving the external case, there are two options: 1) save just the external case, or 2) save the external case and any ties to the original case. Option one just saves the external case, while option two saves the external case and any transmission lines or transformers that connect the external system to the rest of the system. Save just the external case if you are planning to use the external case as a standalone case. Save the external case and its ties if you are planning to modify the external case and then to append it back to the original case.
Click Save External System to save the external system in a file. You will be prompted for the desired case format.
Deleting the External System
This procedure deletes the external system from the original case. All devices in the external system are removed, including any buses and lines/transformers in the external system and any lines/transformers that join the external system to the study system. Check the Remove External Objects from Onelines to remove any display objects linked to the external system from the open onelines.
This command permanently removes the external system from the case; an equivalent system is not created. Select Delete External System to actually delete the system.
Merge Bus Shunts Across Zero Impedance Branches
This procedure merges bus shunts that are across zero-impedance branches.
Merge Bus Shunt Values Above
During the merging process, only will merge bus shunts values above this threshold.
Merge Across Branches
During the merging process, only will merge bus shunts across branches with X, R less than the specified threshold.
Merge Shunts
Press the button to merge the shunt buses as specified by the previous options.