# Three-Phase V-I Measurement

Measure three-phase currents and voltages in circuit

## Library

Simscape / Electrical / Specialized Power Systems / Fundamental Blocks / Measurements

• ## Description

The Three-Phase V-I Measurement block is used to measure instantaneous three-phase voltages and currents in a circuit. When connected in series with three-phase elements, it returns the three phase-to-ground or phase-to-phase peak voltages and currents.

The block can output the voltages and currents in per unit (pu) values or in volts and amperes.

If you choose to measure phase-to-ground voltages in per unit, the block converts the measured voltages based on peak value of nominal phase-to-ground voltage:

where

`${V}_{\text{base}}=\frac{{V}_{\text{nom}}\left(Vrms\right)}{\sqrt{3}}\cdot \sqrt{2}$`

If you choose to measure phase-to-phase voltages in per unit, the block converts the measured voltages based on peak value of nominal phase-to-phase voltage:

where

`${V}_{\text{base}}={V}_{\text{nom}}\left(Vrms\right)\cdot \sqrt{2}$`

If you choose to measure currents in per unit, the block converts the measured currents based on the peak value of the nominal current:

`${I}_{\text{abc}}\left(pu\right)=\frac{{I}_{\text{abc}}\left(A\right)}{{I}_{\text{base}}\left(A\right)}$`

where

`$I\text{base}=\frac{{P}_{\text{base}}}{{V}_{\text{nom}}}\ast \frac{\text{sqrt}\left(2\right)}{\text{sqrt}\left(3\right)}$`

Vnom and Pbase are specified in the Three-Phase V-I Measurement block dialog box.

The steady-state voltage and current phasors measured by the Three-Phase V-I Measurement block can be obtained from the Powergui block by selecting Steady-State Voltages and Currents. The phasor magnitudes displayed in the Powergui stay in peak or RMS values even if the output signals are converted to pu.

## Parameters

Voltage measurement

Select `no` if you do not want to measure three-phase voltage. Select `phase-to-ground` (default) if you want to measure the phase-to-ground voltages. Select `phase-to-phase` if you want to measure the phase-to-phase voltages.

Use a label

If selected, the voltage measurements are sent to a labeled signal. Use a From block to read the voltages. The Goto tag of the From block must correspond to the label specified by the Signal label parameter. If cleared, the voltage measurements are available via the Vabc output of the block. Default is cleared.

Signal label

Specifies a label tag for the voltage measurements. default is `Vabc`.

Voltages in pu, based on peak value of nominal phase-to-ground voltage

If selected, the measured phase-to-ground voltages are converted in pu. Default is cleared.

### Note

For new models, this parameter is not available if the Voltage measurement parameter is set to `phase-to-phase` or `no`. However, this parameter is available and selected for a model saved from a previous release with the Voltage measurement parameter set to `phase-to-phase` and the Voltages in pu option selected. In such a case, you can choose to keep this parameter as is for compatibility purposes. You can also choose to clear this parameter and select the Voltages in pu, based on peak value of nominal phase-to-phase voltage parameter. You then need to take into account the impact of this new per unit conversion in your model

Voltages in pu, based on peak value of nominal phase-to-phase voltage

If selected, the measured phase-to-phase voltages are converted in pu. This parameter is not available if Voltage measurement parameter is set to `phase-to-ground` or `no`. Default is .

Nominal voltage used for pu measurement (Vrms phase-phase)

The nominal voltage, in volts RMS, used to convert the measured voltages in pu. This parameter is not available if the Voltage measurement parameter is set to `no`. Default is `500e3`.

Current measurement

Select `yes` (default) if you want to measure the three-phase currents that flow through the block.

Use a label

If selected, the current measurements are sent to a labeled signal. Use a From block to read the currents. The Goto tag of the From block must correspond to the label specified by the Signal label parameter. If cleared, the current measurements are available via the Iabc output of the block. Default is cleared.

Signal label

Specifies a label tag for the current measurements. Default is `Iabc`.

Currents in pu

If selected, the three-phase currents are measured in pu. Otherwise they are measured in amperes. Default is cleared.

Base power (VA 3 phase)

The three-phase base power, in volt-ampere (VA), used to convert the measured currents in pu. The Base power (VA 3 phase) parameter is not available if Currents in pu is cleared.

Output signals in

Specifies the format of the measured signals when the block is used in a phasor simulation. The Output signals in parameter is enabled when the Simulation type parameter of the powergui block is set to `Phasor` or `Discrete phasor`.

Set to `Complex` (default) to output the measured voltages and currents as complex values. The outputs are complex signals.

Set to `Real-Imag` to output the real and imaginary parts of the measured voltages and currents.

Set to `Magnitude-Angle` to output the magnitudes and angles of the measured voltages and currents.

Set to `Magnitude` to output the magnitudes of the measured voltages and currents. The output is a scalar value.

## Inputs and Outputs

`Vabc`

The three measured phase-to-ground or phase-to-phase voltages. The Vabc output disappears when the Use a label parameter is selected or when the Voltage measurement menu is set to `no`.

`Iabc`

The three measured line currents. The Iabc output disappears when the Use a label parameter is selected or when the Current measurement menu is set to `no`.

## Examples

See the `power_3phseriescomp` example (blocks B1, B2, and B3) for a typical application using the Three-Phase V-I Measurement block.