Transformer Mvar Control Dialog
When used to control reactive power, the LTC transformer always controls the reactive power flow at the from end of the transformer (i.e., the tapped side), with positive flow assumed to be going through the transformer to the to bus. Therefore the regulated bus field is not used.
The Common Options tab of this dialog has the following fields:
Automatic Control Type
This section is only visible on the dialog in edit mode. The control type of the transformer can be changed between no control, voltage regulation, reactive power control, or phase shifter control. Changing the control type will update the dialog to reflect the type of control that is selected.
Mvar Flow at From Bus
The current Mvar flow as measured at the from end of the line. This is the parameter the transformer tries to control.
Mvar Error
If the Mvar flow at the from end violates the limits defined by the Regulation Minimum Mvar Flow and Regulation Maximum Mvar Flow fields, the Mvar Error field indicates by how much the flow falls outside the control range.
Regulation Minimum Mvar Flow, Regulation Maximum Mvar Flow
Minimum and maximum allowable reactive power flow as measured at the from bus. The transformer attempts to regulate the reactive flow to fall within this range.
Regulation Target Type
As long as the regulated Mvar flow is inside the regulation minimum and maximum, the transformer will not change its tap ratio. When the regulated Mvar flow moves outside of this regulation range, Simulator will calculate a new tap ratio in an attempt to bring the regulated Mvar flow back inside of its range. The Regulation Target Type determines what value is used as a target when calculating this change in tap ratio. Middle is the default and means that the target is the average of the regulation minimum and maximum regardless of whether the Mvar flow is high or low. Max/Min means that the regulation maximum is used as the target when the regulated Mvar flow is above the maximum, and regulation minimum is used as the target value when the regulated Mvar flow is below the minimum.
Present Tap Ratio
The transformer's present off-nominal turns ratio.
Minimum Tap Ratio, Maximum Tap Ratio
Minimum and maximum allowable off-nominal tap ratios for the LTC transformer. Typical values are 0.9 and 1.1.
Tap Step Size
Transformer off-nominal turns ratio increment. The off-nominal turns ratio is either incremented or decremented from 1.0 in integer multiples of this value. Default value is 0.00625.
Mvar to Tap Sensitivity
The amount of Mvar shift that would be implemented by switching one tap position from the current position. This sensitivity indicates the ability of the transformer to control Mvars.
Impedance Correction Table
Specifies the number of the transformer's corresponding transformer impedance correction table. Transformer impedance correction tables are used to specify how the impedance of the transformer should change with the off-nominal turns ratio. If this number is 0, no impedance correction table is associated with the transformer, and the impedance of the transformer will thus remain fixed as the tap ratio changes. Valid impedance correction table numbers range from 1 to 63. To assign an existing impedance correction table to the transformer, enter the existing table's number. To view the existing impedance correction tables, click the Insert/View Impedance Correction Table button, which brings up the Transformer Impedance Correction Dialog. To define a brand new impedance correction table for the transformer, enter an unused table number and then click Insert/View Impedance Correction Table to prescribe the correction table. Note that the association between a transformer and an impedance correction table is not finalized until you select either OK or Save on the Branch Information Dialog or Branch Options dialog.
View Transformer Correction Table or Insert Transformer Correction Table
Click on this button either to view or to insert transformer correction tables. Clicking on this button displays the Transformer Impedance Correction Dialog. Note that a table must contain at least two points in order to be defined.
The Time Step Options tab contains control options specific for the Time Step Simulation tool.