Line Geometry

Layout of Conductors for a 735kV Line

Number of phase conductors (bundles)	Specify the number of phase conductors (single conductors or bundles of sub conductors) to be used. This parameter, together with the Number of ground wires (bundles) parameter, will determine the number of rows of the table of conductors.
Number of ground wires (bundles)	Specify the number of ground wires (single conductors or bundles of sub conductors) to be used. Ground wires are usually not bundled. This parameter, together with the Number of phase conductors (bundles) parameter, will determine the number of rows of the table of conductors. In the table of conductors, five rows are visible at a time. If more than five conductors (phase conductors plus ground wires) are specified, a scroll bar appears at the right side of the table to give you access to the different rows of the table.
Phase number	Specify the phase number to which the conductor belongs. Several conductors may have the same phase number. All conductors having the same phase number are lumped together and will be considered as a single equivalent conductor in the R L C matrices. For example, if you want to compute the line parameters of a three-phase line equivalent to a double-circuit line, you specify phase numbers 1, 2, 3 for conductors p1, p2, p3 (circuit 1) and phase numbers 3, 2, 1 for conductors p4, p5, p6 (circuit 2), respectively.

If you prefer to simulate this line as two individual circuits and have access to the six-phase conductors, you would rather specify phase numbers 1, 2, 3, 6, 5, 4 respectively for conductors p1, p2, p3, p4, p5 and p6.
In three-phase systems, the three phases are usually labeled A, B, C. The correspondence with the phase number is 1, 2, 3, 4, 5, 6, 7, 8, 9,. = A, B, C, A, B, C A, B, C.
You can also use the phase number to lump conductors of an asymmetrical bundle. For ground wires, the phase number is forced to zero. All ground wires are lumped with the ground and they do not contribute to the R L C matrix dimensions.

Note: If you need to access the ground wire connections in your model, you must specify these ground wires as normal phase conductors and connect them to the ground by yourself.

X	Specify the horizontal position of the conductor in meters or feet. The location of the zero reference position is arbitrary. For a symmetrical line you normally choose X = 0 at the center of the line.
Y tower	Specify the vertical position of the conductor (at the tower) with respect to ground, in meters or feet.
Y min	Specify the vertical position of the conductor with respect to ground at mid-span, in meters or feet. The average height of the conductor is given by:

Where:

Y_tower: height of conductor at tower

Y_min: height of conductor at mid span

sag=Y_tower-Y_min

Instead of specifying two different values for Y_tower and Y_min, you may specify the same Y_average value.

Line Height

Conductor (bundle) type	Specify one of the conductor or bundle type numbers listed in the first column of the table of conductor characteristics.
Compute Electrical parameters	Computes the RLC parameters. After completion of the parameters computation, results are displayed in the window entitled "Electrical Data Parameters"
Display Electrical Values	The displayed electrical parameters are: • R matrix, L matrix, and C matrix parameters. • TI tranformation matrix. • R, L, and C vectors of values for modal parameters. • R, L, and C vectors of self impedance values are displayed for zero & positive sequence parameters. • R, L and C vectors for mutual impedance values between lines are displayed for mutual zero-sequence.
IMPORTANT	The R, L, C parameters are always displayed respectively in ohms/km, henries/km, and farads/km, even if the English units have been used to specify the input parameters.

Conductor & Bundle Characteristics

Details of a Bundle Conductor

Number of conductor types or bundle types	Specify the number of conductor types (single conductor or bundle of subconductors) to be used. This parameter sets the number of rows for the conductors types table.. The phase conductors and ground wires can be either single conductors or bundles of subconductors.
Conductor internal inductance evaluated from...	Select one of the following three parameters to specify how the conductor internal inductance is computed:

1) T/D ratio, 2) Geometric Mean Radius (GMR), or 3) Reactance Xa at 1-foot spacing (or 1- meter spacing if the Units parameter is set to “METRIC”).

(If you select T/D ratio, the internal inductance is computed from the T/D value specified in the table of conductors, assuming a hollow or solid conductor, where D is the conductor diameter and T is the thickness of the conducting material.)

The conductor self-inductance and resistance are computed from the conductor diameter, T/D ratio, DC resistance, and relative permeability of conducting material and specified frequency.
If you select Geometric Mean Radius (GMR), the conductor GMR is used to evaluate the internal inductance. When the conductor inductance is evaluated from the GMR, the specified frequency does not affect the conductor inductance. You have therefore to provide the manufacturer's GMR for the desired frequency (usually 50 Hz or 60 Hz).
Selecting Reactance Xa at 1-foot spacing (or 1-meter spacing) uses the positive sequence reactance at the specified frequency of a three-phase line having 1-foot (or 1- meter) spacing between the three phases to compute the conductor internal inductance.

Include conductor skin effect	Select this check box to include the impact of frequency on conductor AC resistance and inductance (skin effect). If this parameter is not checked, the resistance is kept constant at the value specified by the Conductor DC resistance parameter and the inductance is kept constant at the value computed in DC, using the Conductor outside diameter and the conductor T/D ratio. When skin effect is included, the conductor AC resistance and inductance are evaluated considering a hollow conductor with T/D ratio (or solid conductor if T/D = 0.5). The T/D ratio is used to evaluate the AC resistance even if the conductor inductance is evaluated from the GMR or from the reactance at one-foot spacing or one-meter spacing. The ground skin effect is always considered and it depends on the ground resistivity.
Conductor (bundle) type	Lists the conductor or bundle types by increasing number, starting from 1 and ending at the value specified in the parameter Number of conductor types or bundle types.
Conductor outside diameter	Specify the conductor outside diameter in centimeters or inches.
Conductor T/D ratio	A T/D value of 0.5 indicates a solid conductor. Specify the T/D ratio of the hollow conductor, where T is the thickness of conducting material and D is the outside diameter. This parameter can vary between 0 and 0.5.

For Aluminum Cable Steel Reinforced (ACSR) conductors, you can ignore the steel core and consider a hollow aluminum conductor (typical T/D ratios comprised between 0.3 and 0.4).

The T/D ratio is used to compute the conductor AC resistance when the “Include conductor skin effect” parameter is checked. It is also used to compute the conductor self inductance when the parameter box “Conductor internal inductance evaluated from” is set to T/D ratio.

Conductor GMR	This parameter is accessible only when the parameter box “Conductor internal inductance evaluated from” is set to Geometric Mean Radius (GMR). Specify the GMR in centimeters or inches. The GMR at 60 Hz or 50 Hz is usually provided by conductor manufacturers. When the parameter box “Conductor internal inductance evaluated from” is set to T/D ratio, the value of the corresponding GMR giving the same conductor inductance is displayed. When the parameter box “Conductor internal inductance evaluated from” is set to Reactance Xa at 1- foot spacing or (1-meter spacing), the title of the column changes to the parameter name as explained below.
Conductor relative permeability	Specify the relative permeability r of the conducting material. r = 1.0 for nonmagnetic conductors (aluminum, copper). This parameter is not accessible when the “Include conductor skin effect” parameter is not checked.
Number of conductors per bundle	Specify the number of subconductors in the bundle or 1 for single conductors.
Bundle diameter	Specify the bundle diameter in centimeters or inches. This parameter is not accessible when the Number of conductors per bundle is set to 1. When you specify bundled conductors, the subconductors are assumed to be evenly spaced on a circle. If this is not the case, you must enter individual subconductor positions in the Line Geometry table and lump these subconductors together by giving them the same Phase number parameter.
Angle of conductor 1	Specify an angle in degrees that determines the position of the first conductor in the bundle with respect to a horizontal line parallel to ground. This angle determines the bundle orientation. This parameter is not accessible when the number of “Conductors per bundle” is set to 1.
Transposition options The transposition options are:
Unstransposed	A constant real transformation matrix is deternined automatically by the program with the eigenanalysis routines.
Transposed	The line is modelled as perfectly transposed. The generalized Clarke transformation is used for an m-phase line.
Transposed by 3 phases	Applies only to the double-circuit lines. It is assumed that there is only zero-sequence coupling between the two seperate circuits. Each circuit is perfectly balanced.