Two windings transformer

The com.powsybl.iidm.network.TwoWindingsTransformer interface is used to model a two windings power transformer. A two windings power transformer is connected to two voltage levels (side 1 and side 2) that belong to a same substation. A ratio tap changer and/or a phase tap changer can be associated with a two windings power transformer.

Characteristics

Attribute	Type	Unit	Required	Default value	Description
id	string	-	yes	-	Unique identifier of the transformer
name	string	-	yes	-	Human-readable name of the transformer
$r_{nom}$	double	$\Omega$	yes	-	The nominal series resistance at the side 2 of the transformer
$x_{nom}$	double	$\Omega$	yes	-	The nominal series reactance at the side 2 of the transformer
$g_{nom}$	double	S	yes	-	The nominal magnetizing conductance at the side 2 of the transformer
$b_{nom}$	double	S	yes	-	The nominal magnetizing susceptance at the side 2 of the transformer
$V_{1\ nom}$	double	kV	yes	-	The rated voltage at side 1
$V_{2\ nom}$	double	kV	yes	-	The rated voltage at side 2

Two windings transformers can also have current limits defined for each end.

Model

Two windings transformer are modelled with the following equivalent $\pi$ model:

Power line model

With the series impedance $z$ and the shunt admittance $y$ and the voltage ratio $\rho$ and the angle difference $\alpha$ and potentially parameters from the current step of a ratio tap changer and/or a phase tap changer, we have:

$r=r_{nom}.\left(1+\frac{r_{r, tap} + r_{\phi, tap}}{100}\right)\\ x=x_{nom}.\left(1+\frac{x_{r, tap} + x_{\phi, tap}}{100}\right)\\ g=g_{nom}.\left(1+\frac{g_{r, tap} + g_{\phi, tap}}{100}\right)\\ b=b_{nom}.\left(1+\frac{b_{r, tap} + b_{\phi, tap}}{100}\right)\\ \rho=\frac{V_{2nom}}{V_{1nom}}.\rho_{r, tap}.\rho_{\phi, tap}\\ \alpha=\alpha_{\phi, tap}\\ z=r+j.x\\ y=g+j.b\\ V_{0}=V_{1}.\rho e^{j\alpha}\\ I_{0}=\frac{I_{1}}{\rho e^{-j\alpha}}\\$

Using the above notation, the equations of the two windings transformer, in complex notations, are as follow:

$\left(\begin{array}{c} I_{1}\\ I_{2} \end{array}\right)=\left(\begin{array}{cc} \rho\text{²}(y+\frac{1}{z}) & -\rho e^{-j\alpha}\frac{1}{z}\\ -\rho e^{j\alpha}\frac{1}{z} & \frac{1}{z} \end{array}\right)\left(\begin{array}{c} V_{1}\\ V_{2} \end{array}\right)$

Examples

This example shows how to create a two windings transformer in the network:

TwoWindingsTransformer twoWindingsTransformer = substation.newTwoWindingsTransformer()
    .setId("TWT2")
    .setName("My two windings transformer")
    .setVoltageLevel1("VL1")
    .setVoltageLevel2("VL2")
    .setNode1(1)
    .setNode2(2)
    .setR(0.5)
    .setX(4)
    .setG(0)
    .setB(0)
    .setRatedU1(24)
    .setRatedU2(385)
    .add();