Linear Transformer (Power System Blockset)

Power System Blockset

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Linear Transformer

Examples See Also

Implement a two- or three-winding linear transformer

Library

Elements Library

Description

The Linear Transformer block model shown below consists of three coupled windings wound on the same core.

The model takes into account the winding resistances (R1 R2 R3), the leakage inductances (L1 L2 L3), as well as the magnetizing characteristics of the core which is modeled by a linear (Rm Lm) branch.

To comply with industry practice, you must specify the resistance and inductances per unit (pu) based on the transformer rated power (Pn in VA) and nominal voltage of the winding (V_n in V_rms). The base resistance and inductance are defined as follows:

For example, for the default parameters of winding one specified in the dialog box section:

Dialog Box

Specify in the first entry the nominal power rating and frequency of the transformer. Then specify in the following three entries the parameters of each winding (nominal voltage in volts rms, resistance and leakage inductance in pu). Specify in the last entry the resistance and inductance simulating the core active and reactive losses both in pu.

Inputs and Outputs

Input one, output one, and output three (if it exists) are at the same instantaneous polarity. If you set the entry for the third winding to zero, the block will become a transformer with two windings and a new icon will be displayed:

Limitations

Because of modeling constraints the following restrictions apply: The winding resistances cannot be set to zero, however leakage inductances can be set to zero. Use values as small as necessary to simulate quasi-zero resistances. Similarly, the magnetizing resistance Rm must have a finite value but the reactive magnetizing losses can be set to zero by specifying Lm=Inf.

Windings can be left floating (i.e, not connected by an impedance to the rest of the circuit). The floating winding will be connected internally to the main circuit through a resistor. This invisible connection does not affect voltage and current measurements.

Example

Typical residential distribution transformer network feeding line to neutral and line to line loads. This circuit is available in the psbtransformer.mdl file.