Simulator 16 User Guide - PowerWorld

Branch Options: Transformer Control
Transformers are used to transfer power between different voltage levels or to regulate real or
reactive flow through a particular transmission corridor. Most transformers come equipped with taps
on the windings to adjust either the voltage transformation or the reactive flow through the
transformer. Such transformers are called either load-tap-changing (LTC) transformers or tapchanging-under-load
(TCUL) transformers.
Another type of transformer is known as a phase-shifting transformer (phase shifter or phase angle
regulator). Phase-shifting transformers, which are less common than LTC transformers, vary the angle
of the phase shift across the transformer in order to control the MW power flow through the
transformer.
Options for specifying transformer control are found on the Transformer Control tab of the Branch
Options dialog when in Edit mode and the Transformer tab of the Branch Information Dialog when in
Run mode.
Off-nominal Turns Ratio and Phase Shift Degrees
The Off-nominal Turns Ratio field indicates the voltage transformation, while the Phase Shift
Degrees field show the phase shift angle. If the transformer is not on automatic control, these
values can be changed manually. The off-nominal tap ratio determines the additional transformation
relative to the nominal transformation. This value normally ranges from 0.9 to 1.1 (1.0 corresponds
to no additional transformation). For phase-shifting transformers the phase shift value normally
ranges from about -40 to 40. The phase angle field can be non-zero for LTC and fixed
transformers, most notably +/- 30 if the transformer configuration is a delta-wye or wye-delta
configuration. The transformer configuration is very important when performing a fault analysis
study.
Automatic Control Type provides the type of transformer. Valid types are 1) No Automatic Control
(in which the taps are assumed fixed), 2) voltage regulation (AVR), 3) Reactive Power Control, and 4)
Phase Shift Control.
Simulator provides you with a great deal of flexibility in being able to specify which transformers will
actually be used for automatic control in the Power Flow Solution. For a transformer to be used for
voltage or flow control, three criteria must be met:
For an LTC transformer, the transformer's Automatic Control Enabled field must be checked.
This field can also be modified on the Transformer Records display. When the transformer is a
phase shifter, the Automatic Control Enabled field has three options. Select Not Enabled to
completely disable the phase shifter for automatic control. Select Enabled for Power Flow to allow
automatic control actions during the power flow solution. Select Enabled for OPF Only to allow the
phase shifter to be a control as part of the OPF solution but not on automatic control as part of the
power flow solution.
The transformer's area must have automatic transformer control enabled. This is specified on the
Options Tabof the Area Records display.
Transformer control must not be disabled for the entire case. This is specified on the Power Flow
Solution Tab of the Simulator Options Dialog. Automatic control for LTC transformers and phase
shifters can be disabled separately at the case level.
The type of transformer can be changed on the Transformer Control Info dialog opened by clicking
the Change Automatic Control Options... button. This dialog contains different information
depending on the type of transformer control that is selected. The Common Options tab of this
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