Simulator 16 User Guide - PowerWorld

Shows the sensitivity of the voltage magnitude at the regulated bus to a change in the
transformer's tap ratio. You can use this field to assess whether or not the transformer can
effectively control the regulated bus voltage. In an ideal case, such as when the LTC transformer
is being used to control the voltage at a radial load bus, the sensitivity is close to 1.0 (or -1.0
depending upon whether the tapped side of the transformer is on the load side or opposite side
of the transformer). However, sometimes the transformer is very ineffective in controlling the
voltage. This is indicated by the absolute value of the sensitivity approaching 0. A common
example is a generator step-up transformer trying to control its high-side voltage when the
generator is off-line. Simulator automatically disables transformer control if the transformer
sensitivity is below the value specified on Power Flow Solution Tab of the Simulator Options
dialog.
Line Drop/Reactive Current Compensation
Typical specification of the bus at which the voltage should be controlled by a transformer is an
actual bus in the power system model. However, some control schemes require that the voltage
at some fictitious bus a specified impedance away from the transformer be controlled instead.
This can be accomplished using the line drop and reactive current compensation control method.
This method requires that the regulated bus for a transformer be specified as one of the
transformer's terminal buses. This provides a reference point for specifying the location of the
fictitious bus that is the actual controlled point. An impedance must also be specified that will
determine the location of the fictitious bus in reference to the selected regulated bus.
Check the Use Line Drop/Reactive Current Compensation checkbox to use this control
method. Specify the impedance for the location of the fictitious controlled bus using the Line
Drop/Reactive Current Compensation Resistance (R) and Line Drop/Reactive Current
Compensation Reactance (X) fields. The impedance should be specified in per-unit.
Impedance Correction Table
This field 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,
then 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.
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