Since R2021a

Libraries:
Simscape / Electrical / Passive

## Description

The Constant Current Load (Three-Phase) block implements a constant current load for a three-phase supply.

This block consumes a current equal to the value of the Consumed current (RMS) parameter as long as the voltage from the three-phase supply is equal to or greater than the value specified for the Minimum supply voltage (phase-to-phase RMS) parameter.

When the voltage from the three-phase supply drops below the value of Minimum supply voltage (phase-to-phase RMS), the load behaviour changes and the block models a load with constant resistance.

### Equations

If the three-phase voltages are balanced, the phase-to-phase RMS voltage is defined by this equation:

${V}_{lin{e}_{RMS}}=\sqrt{{\left({v}_{a}-{v}_{dc}\right)}^{2}+{\left({v}_{b}-{v}_{dc}\right)}^{2}+{\left({v}_{c}-{v}_{dc}\right)}^{2}},$

where ${v}_{dc}=\frac{{v}_{a}+{v}_{b}+{v}_{c}}{3}.$

The currents for each of the three phases are defined by this equation:

${i}_{k}\left(t\right)=\frac{{v}_{k}\left(t\right)}{{R}_{equiv}},$

where Requiv is the equivalent resistance and depends on value of the Minimum supply voltage (phase-to-phase RMS) parameter.

If the voltage from the three-phase supply is greater than the value specified for the Minimum supply voltage (phase-to-phase RMS) parameter, the equivalent resistance is defined by:

${R}_{equiv}=\frac{\frac{{v}_{pk}}{\sqrt{2}}}{{I}_{RM{S}_{consumed}}},$

where vpk is the voltage peak magnitude and IRMSconsumed is the value of the Consumed current (RMS) parameter.

If the voltage from the three-phase supply is less than the value specified for the Minimum supply voltage (phase-to-phase RMS) parameter, the equivalent resistance is defined by:

${R}_{equiv}=\frac{{v}_{phRM{S}_{min}}}{{I}_{RM{S}_{consumed}}},$

where ${v}_{phRM{S}_{min}}=\frac{{v}_{lineRM{S}_{min}}}{\sqrt{3}}$ is the phase-to-ground RMS minimum voltage.

### Faults

To model a fault in the Constant Current Load (Three-Phase) block, in the Faults section, click the Add fault hyperlink next to the fault that you want to model. In the Add Fault window, specify the fault properties. For more information about fault modeling, see Fault Behavior Modeling and Fault Triggering.

The Constant Current Load (Three-Phase) block allows you to model an electrical fault as an open circuit. The block can trigger fault events either:

• At a specific time

• When a power limit is exceeded for longer than a specific time interval

If the block is in a network that is compatible with frequency-time simulation mode, you can perform a load-flow analysis on the network. A load-flow analysis provides steady-state values that you can use to initialize a machine.

For more information, see Perform a Load-Flow Analysis Using Simscape Electrical and Frequency and Time Simulation Mode.

## Ports

### Conserving

expand all

Expandable three-phase electrical port associated with the three-phase voltage.

## Parameters

expand all

Whether to model composite or expanded three-phase ports.

Composite three-phase ports represent three individual electrical conserving ports with a single block port. You can use composite three-phase ports to build models that correspond to single-line diagrams of three-phase electrical systems.

Expanded three-phase ports represent the individual phases of a three-phase system using three separate electrical conserving ports.

### Main

Root mean square current consumed by the block.

Minimum voltage, in phase-to-phase RMS, that the supply must provide for the block to act as a current load.

### Faults

Option to add an open-circuit fault in the Constant Current Load (Three-Phase) block.

Conductance during the open-circuit state.

#### Dependencies

To enable this parameter, add a fault to the Constant Current Load (Three-Phase) block by clicking the Add fault hyperlink in the Open circuit fault parameter.

After you create the fault, you can change the properties in the Fault Inspector window. When you open a block that has a fault, the Open Fault Inspector hyperlink appears instead of the Add fault hyperlink. For an example that shows how to include faults, see Analyze a DC Armature Winding Fault.

Simulation time at which the block enters the faulted state.

#### Dependencies

To enable this parameter, in the Fault Inspector window, set Trigger Type to Timed.

This parameter appears in the Trigger section of the Fault Inspector window. For more information, see Set Fault Triggers.

Maximum permissible power value. If the power exceeds this value for longer than the Time to fail when exceeding power parameter value, then the block enters the faulted state.

#### Dependencies

To enable this parameter, in the Fault Inspector window, set Trigger Type to Behavioral.

This parameter appears in the Trigger section of the Fault Inspector window. For more information, see Set Fault Triggers.

Maximum length of time that the power can exceed the maximum permissible value without triggering the fault.

#### Dependencies

To enable this parameter, in the Fault Inspector window, set Trigger Type to Behavioral.

This parameter appears in the Trigger section of the Fault Inspector window. For more information, see Set Fault Triggers.

## Version History

Introduced in R2021a