The Change | Nominal kV command in the Main Window lets you change the nominal kV of one or more buses that are connected via transmission lines and switches. Depending on the options you specify, the program will also modify the impedances and tap voltages of the network elements that are connected to one or more of the affected buses. You must select a bus before executing this command.
TO CHANGE THE NOMINAL kV:
1. Select a bus by clicking the left mouse button once on its symbol.
The bus symbol will turn dotted red when selected. Your selection will define a set of buses that are connected via transmission lines and switches. The nominal kV of these buses will be changed by this command.
2. Select the Network | Change | Nominal kV command.
A dialog box will appear to let you specify the new nominal kV and whether or not to modify the network impedances and transformer taps. The number of affected buses is shown at the top.
3. Press the "Bus List" Button to see a list of buses that will be affected by this command.
4. Input the new nominal kV in the edit box.
5. Specify update options on PU Impedances (excluding those of transformer).
This option will affect all the network elements (generators, shunts, loads, transmission lines, switches and phase shifters) that are connected to one or more of the affected buses. None of these options will automatically change the MW and MVAR of the loads or the per-unit impedances of the phase shifters.
Do not change: Click this button if you want the program NOT to change any of the per-unit impedances of transmission lines, generators and shunts.
Update automatically for the new nominal kV: Click this button if you want the program to recalculate the per-unit impedances for the new nominal kV. The program will scale the per-unit impedances of transmission lines, generators and shunts by the ratio (kVold/kVnew)**2.
Update manually one by one: Click this button if you want to change the parameters for each piece of equipment by hand. A series of Info dialog boxes will appear to let you modify the parameters.
The mutual coupling impedances are updated automatically if your option is not set to “Do not change.”
6. Specify update options on Transformer taps.
This option will affect all the 2- and 3-winding transformers that are connected to one or more of the affected buses. None of these options will automatically change the per-unit impedance of the transformers.
Do not change: Click this button if you want the program NOT to change the transformer tap voltages.
Update automatically to the new nominal kV: Click this button if you want the program to automatically reset the transformer tap voltages to the new nominal kV.
Update manually one by one: Click this button if you want to change the tap voltages and the per-unit impedances for each transformer by hand. A series of Info dialog boxes will appear to let you modify the transformer parameters.
7. Press OK.
The program will change the nominal kV of the affected buses. Depending on the options you specified, the program will automatically update the per-unit impedances and transformer tap voltages, or will display a series of Info dialog boxes to let you update them manually.
Note: The default option is to have the program (1) adjust the per-unit impedances of generators, shunts, transmission lines and the mutual-coupling parameters automatically for the new nominal kV, and (2) not change the transformer taps, the per-unit impedances of transformers and phase shifters, the MW and MVAR of loads. With these options and in the absence of loads on the affected buses, the fault impedances will remain the same before and after the nominal kV changes.
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