Make-Up Power Sources

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Generator, load, injection group, and switched shunt contingencies may cause imbalances between generated power and demand. The default way to handle these imbalances is to assign them to the system slack. There are other global options that can be specified for contingency analysis as a whole to deal with make-up power. The global settings are the preferred way of dealing with make-up power, but more specific compensation for make-up power can be specified for certain contingency actions.

To implement more local compensation for generation, load, injection group, and switched shunt changes, use the Make-Up Power Sources Dialog. This dialog can be accessed by from the Contingency Element Dialog by clicking the button labeled Make-Up Power Sources. Most of the dialog is occupied by a grid that lists bus numbers and relative contributions. This grid is a Case Information Display, so its behavior should be familiar. For example, right-click on the grid to display its local menu.

We shall call those buses that must compensate for the changes caused by a generator, load, injection group, or switched shunt contingency "compensators". To insert a new compensator, select Insert from the grid’s local menu. This opens another dialog, where you should specify the bus number of the compensator and its contribution. Specify the contribution of the compensator either as a percentage or as a fixed number of MW. If a particular contingency has multiple compensators, then the choice of basis for the contribution (either MW or percent) should be consistent for each. After identifying the compensator, click OK. The grid should update with your newly added compensator.

To delete an existing compensator, select it from the grid and select Delete from the local menu.

To determine how much each compensator contributes to the imbalance, each contribution value is normalized to the total sum of all contribution values. This allows the values to be entered in either percent or MW. Keep in mind that when entering the values in percent that the sum of all contribution values should equal 100 or the actual contribution amounts will not occur in the expected percentages.

Compensators account for the changes caused by a generator, load, injection group, or switched shunt contingency by changing either generation or load to satisfy its defined contribution. For example, suppose compensator contributions are specified as percentages, and Simulator needs to compensate for 100 MW lost in a particular generation contingency. Suppose the contingency has 4 compensators defined as follows:

Bus Number Contribution

1  20

2  30

3  10

4  40

Suppose buses 1 and 2 are load buses, and buses 3 and 4 are generators. Then bus 1’s load will decrease by 20 MW, bus 2’s load will decrease by 30 MW, bus 3’s generation will increase by 10 MW, and bus 4’s generation will increase by 40 MW. These changes will be instituted regardless of the compensators’ operating limits or AGC status. In fact, any compensating units will be set off AGC to ensure that the prevailing AGC control does not distort the dictates of the contingency. Furthermore, maximum MW limits on generators will not be checked.

If a compensator has both generators and loads attached to it, the generator will take precedence. The generator will function as the compensating device, and the load will be left unchanged.