Three-Phase Tap-Changing Transformer (Three-Windings)

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

Winding connection for winding 1.

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

Winding connection for winding 2.

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

Winding connection for winding 3.

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

Select Three single-phase transformers to implement a three-phase transformer using three single-phase transformer models. This core type is used in very large power transformers found in utility grids.

Select Three-limb core (core type) to implement a three-limb core three-phase transformer. In most applications, three-phase transformers use a three-limb core (core-type transformer). Selecting this core type will produce accurate results during an asymmetrical fault for both linear and nonlinear models (including saturation). During asymmetrical voltage conditions, the zero-sequence flux of a core-type transformer returns outside the core, through an air gap, structural steel, and tank. Consequently, the natural zero-sequence inductance L0 (without delta winding) of a core-type transformer is usually very low (typically 0.3 pu < L0 < 2 pu) compared with a three-phase transformer that uses three single-phase units (L0 > 100 pu). This low L0 value affects voltages, currents, and flux unbalances during linear and saturated operation.

Inductance L0, in pu, of the three-limb core transformer.

Dependencies

To enable this parameter, set Core Type to Three-limb core (core type).

Magnetization resistance Rm, in pu.

Magnetization inductance Lm, in pu, for a nonsaturable core.

Dependencies

To enable this parameter, clear Simulate saturation.

Select this parameter to implement a saturable three-phase transformer.

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

Dependencies

To enable this parameter, select Simulate saturation.

If selected, the initial fluxes are defined by the [phi0A, phi0B, phi0C] (pu) parameter.

When the Specify initial fluxes parameter is cleared, the Simscape Electrical Specialized Power Systems software automatically computes the initial fluxes to start the simulation in steady state. The computed values are saved in the Initial Fluxes parameter and overwrite any previous values.

Dependencies

To enable this parameter, select Simulate saturation.

Initial fluxes for each phase of the transformer.

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

Dependencies

To enable this parameter, select Simulate saturation and Specify initial fluxes.

Select Winding voltages to measure the voltage across the winding terminals.

Select Winding currents to measure the current flowing through the windings.

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

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

Select All measurements (V I Fluxes) 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 simulation. In the Available Measurements parameter of the Multimeter block, the measurements are identified by a label followed by the block name.

Minimum tap position of the transformer. This value is typically between -20 and +20. At the minimum tap position, the transformer voltage ratio is:

U2/U1 = 1 /( 1+ Minimum tap position * Voltage step per tap (pu)).

For example, for a minimum tap position of -20 and a voltage step of 0.015, the voltage ratio is:

U2/U1 = 1/(1+ -20*0.015) = 1.428 pu.

Maximum tap position of the transformer. This value is typically between -20 and +20. At the maximum tap position, the transformer voltage ratio is:

U2/U1 = 1 /(1+ Maximum tap position * Voltage step per tap (pu)).

For example, for a maximum tap position of +20 and a voltage step of 0.015, the voltage ratio is:

U2/U1 = 1/(1+ 20*0.015) = 0.769 pu.

Initial position of the tap when the simulation starts. The initial position must be a value between the minimum tap position and the maximum tap position. When the tap position is 0, the transformer voltage ratio is equal to 1 pu (nominal value).

Voltage step between two taps of the transformer, in pu. This value is typically in the order of 0.01 to 0.05 pu.

The transformer voltage ratio is given by:

U2/U1 = 1 /(1+ Tap position * Voltage step per tap (pu)).

For example, a voltage step per tap value of 0.015, and a tap position of -20, would produce a voltage ratio of:

U2/U1 = 1/(1+ -20*0.015) = 1.428 pu.

The value of the Voltage step per tap (pu) parameter must be chosen in accordance with the value specified for the Minimum tap position parameter. Follow this constraint according to the above equation:

Minimum tap position * Voltage step per tap > -1

For example, for a Voltage step per tap (pu) parameter of 0.05 pu, the minimum value you can specify for the Minimum tap position parameter is: -19. A value of –20 gives an infinite voltage ratio and a value lower than -20 yields to a negative voltage ratio, which is not relevant.

Time for the tap to move from one position to the next. This value is typically between 3 and 10 seconds.

Select Tap control to control the tap position of the transformer with the ctrl input signal. Select Voltage regulation to control the tap position of the transformer using an internal voltage regulator monitoring the Vm (pu) input signal.

Control value at which the tap changes position. To increase the tap position, apply a control signal ctrl greater than this value. To lower the tap position, apply a control signal ctrl smaller than the negative of this value.

Dependencies

To enable this parameter, set Mode to Tap control.

Reference voltage of the voltage regulator, in pu.

Dependencies

To enable this parameter, set Mode to Voltage regulation.

Dead band of the voltage regulator, in pu.

Reference voltage of the voltage regulator, in pu.

Dependencies

To enable this parameter, set Mode to Voltage regulation.

Delay of the voltage regulator, in sec.

Dependencies

To enable this parameter, set Mode to Voltage regulation.