Three-Phase Transformer (Three Windings) - Implement three-phase transformer with configurable winding connections

Library

Elements

Description

This block implements a three-phase transformer by using three single-phase transformers with three windings. You can simulate the saturable core or not simply by setting the appropriate check box in the parameter menu of the block. See the Linear Transformer and Saturable Transformer block sections for a detailed description of the electrical model of a single-phase transformer.

The three windings of the transformer can be connected in the following manner:

Y
Y with accessible neutral (for windings 1 and 3 only)
Grounded Y
Delta (D1), delta lagging Y by 30 degrees

Delta (D11), delta leading Y by 30 degrees

Note The D1 and D11 notations refer to the following clock convention. It assumes that the reference Y voltage phasor is at noon (12) on a clock display. D1 and D11 refer respectively to 1 PM (delta voltages lagging Y voltages by 30 degrees) and 11 AM (delta voltages leading Y voltages by 30 degrees).

The block takes into account the connection type you select, and the icon of the block is automatically updated. An input port labeled N is added to the block if you select the Y connection with accessible neutral for winding 1. If you ask for an accessible neutral on winding 3, an extra outport port labeled n3 is generated.

The saturation characteristic, when activated, is the same as the one described for the Saturable Transformer block, and the icon of the block is automatically updated. If the fluxes are not specified, the initial values are automatically adjusted so that the simulation starts in steady state.

The leakage inductances and resistance of each winding are given in pu based on the transformer nominal power Pn and on the nominal voltage of the winding (V1, V2, or V3). For an explanation of per units, refer to the Linear Transformer and to the Saturable Transformer.

Dialog Box and Parameters

Configuration Tab

Winding 1 connection (ABC terminals)

The winding connection for winding 1.

Winding 2 connection (abc-2 terminals)

The winding connection for winding 2.

Winding 3 connection (abc-3 terminals)

The winding connection for winding 3.

Saturable core

If selected, implements a saturable three-phase transformer. See also the Saturation characteristic parameter on the Parameters tab.

Simulate hysteresis

Select to model a saturation characteristic including hysteresis instead of a single-valued saturation curve. This parameter is visible only if the Saturable core parameter is selected.

Hysteresis Mat file

This parameter is visible only if the Simulate hysteresis parameter is selected.

Specify a .mat file containing the data to be used for the hysteresis model. When you open the Hysteresis Design Tool of the Powergui, the default hysteresis loop and parameters saved in the hysteresis.mat file are displayed. Use the Load button of the Hysteresis Design tool to load another .mat file. Use the Save button of the Hysteresis Design tool to save your model in a new .mat file.

Specify initial fluxes

If selected, the initial fluxes are defined by the Initial fluxes parameter on the Parameters tab. The Specify initial fluxes parameter is visible only if the Saturable core parameter is selected.

When the Specify initial fluxes parameter is not selected upon simulation, SimPowerSystems software automatically computes the initial fluxes to start the simulation in steady state. The computed values are saved in the Initial Fluxes parameter and will overwrite any previous values.

Measurements

Select Winding voltages to measure the voltage across the winding terminals of the Three-Phase Transformer block.

Select Winding currents to measure the current flowing through the windings of the Three-Phase Transformer block.

Select Fluxes and excitation currents (Im + IRm) to measure the flux linkage, in volt seconds (V.s), and the total excitation current including iron losses modeled by Rm (for saturable transformers only).

Select Fluxes and magnetization currents (Im) to measure the flux linkage, in volt seconds (V.s), and the magnetization current, in amperes (A), not including iron losses modeled by Rm (for saturable transformers only).

Select All measurements (V, I, Flux) to measure the winding voltages, currents, magnetization currents, and the flux linkages.

Place a Multimeter block in your model to display the selected measurements during the simulation. In the Available Measurements list box of the Multimeter block, the measurements are identified by a label followed by the block name.

If the Winding 1 connection (ABC terminals) parameter is set to Y, Yn, or Yg, the labels are as follows.

Measurement	Label
Winding 1 voltages	`Uan_w1:, Ubn_w1:, Ucn_w1:` or `Uag_w1:, Ubg_w1:, Ucg_w1:`
Winding 1 currents	`Ian_w1:, Ibn_w1:, Icn_w1:` or `Iag_w1:, Ibg_w1:, Icg_w1:`
Flux linkages	`Flux_A:, Flux_B:, Flux_C:`
Magnetization currents	`Imag_A:, Imag_B:, Imag_C:`
Excitation currents	`Iexc_A:, Iexc_B:, Iexc_C:`

The same labels apply for winding 2 and winding 3, except that the 1 is replaced by 2 or by 3 in the labels.

If the Winding 1 connection (ABC terminals) parameter is set to Delta (D11) or Delta (D1), the labels are as follows.

Measurement	Label
Winding 1 voltages	`Uab_w1:, Ubc_w1:, Uca_w1:`
Winding 1 currents	`Iab_w1:, Ibc_w1:, Ica_w1:`
Flux linkages	`Flux_A:, Flux_B:, Flux_C:`
Magnetization currents	`Imag_A:, Imag_B:, Imag_C:`
Excitation currents	`Iexc_A:, Iexc_B:, Iexc_C:`

Parameters Tab

Units

Specify the units used to enter the parameters of the Three Phase Transformer block. Select pu to use per unit. Select SI to use SI units. Changing the Units parameter from pu to SI, or from SI to pu, will automatically convert the parameters displayed in the mask of the block.

Nominal power and frequency

The nominal power rating, in volt-amperes (VA), and nominal frequency, in hertz (Hz), of the transformer.

Winding 1 parameters

The phase-to-phase nominal voltage in volts RMS, resistance, and leakage inductance in pu for winding 1.

Winding 2 parameters

The phase-to-phase nominal voltage in volts RMS, resistance, and leakage inductance in pu for winding 2.

Winding 3 parameters

The phase-to-phase nominal voltage in volts RMS, resistance, and leakage inductance in pu for winding 3.

Magnetization resistance Rm

The magnetization resistance Rm, in pu.

Magnetization inductance Lm

The magnetization inductance Lm, in pu, for a nonsaturable core. The Magnetization inductance Lm parameter is not accessible if the Saturable core parameter is selected.

Saturation characteristic

This parameter is accessible only if the Saturable core parameter is selected.

The saturation characteristic for the saturable core. Specify a series of current/ flux pairs (in pu) starting with the pair (0,0).

Initial fluxes

Specifies initial fluxes for each phase of the transformer. This parameter is visible only if the Specify initial fluxes and Saturable core parameters are selected on the Configuration tab.

Advanced Tab

Break Algebraic loop in discrete saturation model: When you use the block in a discrete system, you will get an algebraic loop. This algebraic loop, which is required in most cases to get an accurate solution, tends to slow down the simulation. However, to speed up the simulation, in some circumstances, you can disable the algebraic loop by selecting Break Algebraic loop in discrete saturation model. You should be aware that disabling the algebraic loop introduces a one-simulation-step time delay in the model. This can cause numerical oscillations if the sample time is too large.

Example

The power_transfo3wdn circuit uses two Three-Phase Transformer blocks. Two Multimeter blocks are used to measure the phase A voltage (or AB for delta connections) of each winding