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

Three-phase tap-changing transformer

Since R2021b

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Libraries:
Simscape / Electrical / Specialized Power Systems / Power Grid Elements

Description

The Three-Phase Tap-Changing Transformer (Two Windings) block models a three-phase, tap-changing transformer with two windings. The tap changer is on winding 1. Winding 1 is connected in wye. Winding 2 can be connected in wye or delta.

The transformer voltage ratio is determined by the position of the tap and by the method used to control it. When Mode is set to Tap control, the position of the tap is controlled by the input signal. When Mode is set to Voltage regulation, the position of the tap is controlled by an internal voltage regulator that compares the input signal to the reference voltage.

When you use a Three-Phase Tap-Changing Transformer block, set the powergui block Simulation type to Discrete and select Automatically handle Discrete solver. The robust discrete solver is used to discretize the electrical model. Simulink® returns an error if the robust discrete solver is not used.

Examples

OLTC Regulating Transformer

OLTC Regulating Transformer

A tap-changing transformer that regulates positive sequence voltage at a 25 kV bus

Ports

Conserving

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Electrical conserving port associated with the phase A terminal of winding 1.

Electrical conserving port associated with the phase B terminal of winding 1.

Electrical conserving port associated with the phase C terminal of winding 1.

Electrical conserving port associated with the neutral terminal of winding 1.

Electrical conserving port associated with the phase A terminal of winding 2.

Electrical conserving port associated with the phase B terminal of winding 2.

Electrical conserving port associated with the phase C terminal of winding 2.

Simulink

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Signal used to control the tap position of the transformer. The tap position of the transformer increases when the ctrl input signal becomes greater than the specified Threshold parameter value. The tap position decreases when the ctrl input signal becomes less than the negative of the Threshold parameter value.

The new tap position becomes effective after the time specified by the Tap selection time parameter.

Dependencies

To enable this port, set Mode to Tap Control.

Signal used to control the tap position of the transformer with an internal voltage regulator. Use the magnitude of voltage, in pu, measured at the secondary winding or at a remote bus.

The tap position of the transformer increases when the difference between the Vm (pu) input signal and the Reference voltage Vref parameter value becomes greater than the value of the Dead band parameter divided by 2, for a time duration greater than the Delay parameter value.

The tap position decreases when the difference between the Vm (pu) input signal and the Reference voltage Vref (pu) parameter value becomes lower than the value of the negative of the Dead band parameter divided by 2, for a time duration greater than the Delay parameter value.

Dependencies

To enable this port, set Mode to Voltage regulation.

Output signal that gives the current tap position.

Parameters

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Transformer

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.

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.

Tap-Changer

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.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2021b

See Also

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