Component Immittance

Application Overview:

• See Component Immittance Setup for details on user input options for this application.  

• For general details on running an application, selecting and displaying output variables, see Running DEW Applications.  

• The Available Output Variables for the application are described in the last section of this topic.

Immittance is a term applied for either impedance or admittance.  The Immittance Application addresses the calculation of impedances and admittances.

• Immittance is a fundamental DEW application - other applications (i.e. Power Flow, Fault Analysis, etc) will not run without the Immittance application.  

• Results from Immittance application are generated only at runtime and are not stored to the database.

• Immittance calculations may be performed for 60 hertz and harmonics thereof.  The immittance calculations default to 60 hertz.

• For grounded systems, earth resistivity is a function of the specified earth return type.

• For bare conductors, line resistance (i.e. impedance) is dependent upon temperature, thus results may vary with selected month for analysis.

• Default component Sequence Impedances (in ohms) are included in parts database, but may be directly specified via the Sequence Impedance Dialog for particular lines, cables, or transformers.  

• If user specified impedances are available, then these are used in place of impedance values calculated from data stored in the Part Tables.

Application Run / Results:

Impedances (in ohms) are modeled for the following:

• Multi-phase  (i.e. any combination of phases A, B, or C may be present), multi-grounded lines and cables with neutral return

• Multi-phase, multi-grounded overhead lines without neutral return

• Multi-phase, ungrounded lines and cables with neutral return

• Three-phase or two-phase, ungrounded overhead lines with no neutral return

• User specified line/cable impedances

• Transformers

• User specified transformer impedances

• Transmission system Thevenin equivalents

• Special loads, such as synchronous motors

• Mutual impedances between lines and cables

Admittances in siemens (i.e., mhos) are modeled for the following:

• Multi-phase, multi-grounded lines and cables with neutral return

• Multi-phase, multi-grounded overhead lines without neutral return

• Multi-phase, ungrounded lines and cables with neutral return

• Three-phase or two-phase, ungrounded overhead lines with no neutral return

Matrix Reduction:

• Depending upon the number of current paths present, either 3x3, 4x4, 5x5, 6x6, or 7x7 primitive immittance matrices are calculated for lines and cables.  

• All primitive immittance matrices are reduced to 3x3 matrices, where all neutral and earth return currents are eliminated from the immittance model.  

• For an ungrounded system, the 3x3 reduced immittance matrix is transformed so that line voltage drops may be calculated the same as for grounded systems.  

• The 3x3 reduced immittance matrices are made available to other applications, such as power flow and fault analysis.  

• Matrices representing impedance, admittance, and mutual coupling between circuits are linked to the component objects in DEW.  

Interactive Run/Results:

The application runs interactively when the Component Immittance Setup Output Option is set for View Component Results.  When run with this setting selected, the user will be prompted with the mouse pointer () to select a component.  Upon selection, the results for the component are displayed in the Component Immittance Results dialog (shown below), where the user can toggle the view between the Impedance and Admittance results via the View radio buttons.  After review, the user can [Pick Component] to select another component for review or can [Close] to complete the interactive run and exit the dialog.
 

Available Output Variables:

The output variables available for display from the Component Immittance application are described in the following table.  They can be setup to display directly on the network drawing, interactively viewed for selected component during the application run, or plotted versus time and distance from the substation.