Two Winding Transformer - LTC (Load Tap Changer) Tab

Load tap changer (LTC) position can be placed on either side of the transformer by selecting From or To. If the transformer does not have an LTC, select None for standard fixed taps. Fixed off-nominal taps can be entered in the main dialog's Tap kV field.

The default is 0.625 but you can type in your own percentage step size both here and in the power flow two-winding transformer temporary dialog box.

Minimum tap kV, which is used to determine the bottom limit that the tap can be adjusted to during a power flow analysis. This value should be the lowest tap on the transformer to get meaningful results. The default of 0.1 kV is not realistic and should be changed to the actual values if the LTC is used.

Maximum tap kV, which is used to determine the upper limit that the tap can be adjusted to during a power flow analysis. This value should be the highest tap on the transformer to get meaningful results. The default of 1500 kV is not realistic and should be changed to the actual values if the LTC is used.

: Control value, which is determined by the Control Type field.

• Voltage: The control value should be entered in per-unit voltage. A typical range would be .975-1.01 per-unit, with 1.0 per-unit as a starting point.
• MVAR: The value should be entered in actual MVAR rather than adjusted per-unit. To determine what MVAR range is appropriate for a given transformer size, determine the MVAR flow without using an LTC, and multiply by .975-1.01 for an approximate starting place. LTC control is much more limited in strength and range than large generator control.

Determines how the LTC model is used.

• Voltage: The LTC attempts to control the voltage of the bus on the other side of the LTC. For example, if the LTC is chosen to be on the From side, voltage will be controlled on the To side.
• MVAR: The LTC attempts to control the MVAR flow through the transformer to a given value.