Transmission Line Data

This dialog box includes the following areas and tabs:

• Connection Information
• Specifications
• Imported Data
• Comments
• Hyperlinks

Figure 1: Transmission Line Data Dialog Box

Connection Information

ID Name: Uniquely identifies the transmission line. This ID name is sometimes referred to as the transmission line name, and can be up to 12 characters long. The names default to X-1, X-2, X-3, and so on as you enter new transmission lines on the one-line diagram, but you can change those names if desired.

From Bus: The bus from which the transmission line connects, which must already exist on the one-line. Ensure that the From Bus has the same base kV as the transmission line's To Bus. For reference, the From Bus base kV is displayed next to the bus name.

To Bus: The bus to which the transmission line connects, which must already exist on the one-line. Ensure that the To Bus has the same base kV as the transmission line's From Bus. For reference, the To Bus base kV is displayed next to the bus name.

Show Entire Line: This check box is selected by default and causes the entire line to be displayed. By clearing the check box, the line is only be shown as a short section at each end with labels indicating the bus to which the other end is attached.

Specifications

Unit: Choose either US or Metric.

No/Phase: Total number of lines modeled. The default of one (1) means one conductor per phase. Two (2) means two conductors in parallel per phase, and so on. When two or more conductors are in parallel, the impedance of the circuit is decreased by that factor. The impedances shown in the dialog box are for one conductor only, and are not based on the No./Phase field. If you enter these values instead of using Calculate, make sure they are for one conductor only. This lets you to easily check handbook values without additional arithmetic. The Calculate button does not consider bundled conductors at this time.

Material: Material (copper, aluminum, aluminum cable steel reinforced, or copper weld).

Size: Conductor size in AWG or MCM. For more information, see the Aluminum Electrical Conductor Handbook.

Length: The length of the line in miles or meters.

Temp: Temperature of the loaded conductor. This can be varied from 25°C to 250°C depending on the type of study being performed. This temperature is used in determining the resistance of the conductor.

Earth Res: Earth resistivity in ohm-meters. This value is used to determine ground impedance. A default value of 100 ohm-meters is typically used when measured data is not available.

GMD: Geometric Mean Distance of the conductor spacing. This value is used to determine the impedance of the line. Typical default values are used based on the kV of the line.

Average Height: Average height of the transmission line in feet. This value is also used to determine the line impedance. Typical default values are used based on the kV of the line.

Impedances

Impedances are described in ohms/mile or ohms/km, except for Xc, which is in megaohm miles or megaohm km. For more information, see the Westinghouse Transmission and Distribution (T&D) book.

R1: Positive sequence resistance.

X1: Positive sequence reactance.

R0: Zero sequence resistance. If you enter this value as zero (0.0), the positive sequence impedance is used.

X0: Zero sequence reactance. If you enter this value as zero (0.0), the positive sequence impedance is used.

Xc: Shunt capacitive reactance. If you enter this value as zero (0.0), "infinity" is assumed.

Xc0: Shunt capacitive zero sequence reactance. If you enter this value as zero (0.0), "infinity" is assumed.

Rating: Conductor rating in amperes. This field is used to determine line overloads in power flow analysis. If you use Calculate, this value is brought from the device library and is for one conductor. EasyPower does not calculate a new rating if there are multiple conductors per phase. You will need to input the proper rating.

Harmonics

Use the Harmonics tab to indicate whether this equipment item is introducing harmonics into your power system.

Resistance Factor

EasyPower offers two methods for calculating R_H:

• Resistance varying with a power of the harmonic (R-EXP):

R_H = R_Fund * H ^R-EXP

• Resistance varying with a percent eddy current factor (%ECF):

R_H = R_Fund * (1+ECF*H²)/(1+ECF)

EasyPower defaults all skin effect correction to R-EXP and a value of 0.5.

Fundamental Amps

Use to set the fundamental amps. The options are as follows:

• Equipment Rating sets Fundm Amps to the equipment rating of the item described in the Specifications tab. 
• User Specified activates the Fundm Amps field, enabling you to specify a value. 

To use fundamental current calculated by power flow, select Calculated from Power Flow in the Summation Fundamental Voltage area of the Harmonics Options > Control dialog box.

Imported Data

This tab is read-only and appears only if you have imported data from an SKM Data Format file. See Importing an SKM Format File for more information.

Comments

See Comments for information.

Hyperlinks

See Hyperlinks for information.

More Information