Three windings transformer

The com.powsybl.iidm.network.ThreeWindingsTransformer interface is used to model a three windings power transformer. A three windings power transformer is connected to three voltage levels (side 1, side 2 and side 3) that belong to the same substation. We usually have:

• Side 1 as the primary side (side with highest rated voltage)
• Side 2 as the secondary side (side with the medium rated voltage)
• Side 3 as the tertiary side (side with the lowest rated voltage)

A Ratio Tap Changer and/or a Phase Tap Changer can be associated to all three sides of a three windings power transformer. Only one Tap Changer (either ratio or phase tap changer) is allowed to be regulating on the equipment at a given time.

# Characteristics

Attribute Type Required Default value Description
Leg1 ThreeWindingsTransformer.Leg yes - The leg at the primary side
Leg2 ThreeWindingsTransformer.Leg yes - The leg at the secondary side
Leg3 ThreeWindingsTransformer.Leg yes - The leg at the tertiary side

Attribute Type Unit Required Default value Description
id string - yes - Unique identifier of the transformer
name string - yes - Human-readable name of the transformer
RatedU0 double kV yes - The rated voltage at the star bus

Three windings transformers can also have current limits defined for each leg.

## Leg

ThreeWindingsTransformer.Leg is a nested interface used to model a leg of a three windings power transformer.

### Characteristics

Attribute Type Unit Required Default value Description
Terminal Terminal - yes - The terminal the leg is connected to
R double $\Omega\$ yes - The nominal series resistance specified at the voltage of the leg
X double $\Omega\$ yes - The nominal series reactance specified at the voltage of the leg
G double S yes - The nominal magnetizing conductance specified at the voltage of the leg
B double S yes - The nominal magnetizing susceptance specified at the voltage of the leg
RatedU double kV yes - The rated voltage
RatedS double MVA no - The normal apparent power

For the leg of a three windings transformer, the normal apparent power shall be identical at both sides (network side and star bus side).

# Model

Three windings transformers are modeled with three legs, where every leg model is electrically equivalent to a two windings transformer. For each leg, the network bus is at side 1 and the star bus is at side 2.

# Examples

This is an example of how to create a new ThreeWindingsTransformer in the network:

ThreeWindingsTransformer threeWindingsTransformer = substation.newThreeWindingsTransformer()
.setId("TWT3")
.setName("TWT3Name")
.setRatedU0(132)
.newLeg1()
.setVoltageLevel("VL1")
.setNode(11)
.setR(17.424)
.setX(1.7424)
.setG(0.00573921028466483)
.setB(0.000573921028466483)
.setRatedU(132.0)
.newLeg2()
.setVoltageLevel("VL2")
.setNode(22)
.setR(1.089)
.setX(0.1089)
.setG(0.0)
.setB(0.0)
.setRatedU(33.0)
.newLeg3()
.setVoltageLevel("VL3")
.setNode(33)
.setR(0.121)
.setX(0.0121)
.setG(0.0)
.setB(0.0)
.setRatedU(11.0)

transformer.addExtension(ThreeWindingsTransformerPhaseAngleClock.class, new ThreeWindingsTransformerPhaseAngleClock(transformer, 10, 1));