Modeling of Transmission Lines GUC（输电线路GUC建模）.pdf

Modeling of Transmission Lines Electric Power Transmission • The electric energy produced at generating stations is transported over high-voltage transmission lines to utilization points. • The trend toward higher voltages is motivated by the increased line capacity while reducing line losses per unit of power transmitted. • The reduction in losses is significant and is an important aspect of energy conservation. • Better use of land is a benefit of the larger capacity. Concept of transmission TRANSMISSION LINE PARAMETERS • An electric transmission line is modeled using series resistance, series inductance, shunt capacitance, and shunt conductance. • The line resistance and inductive reactance are important. • For some studies it is possible to omit the shunt capacitance and conductance and thus simplify the equivalent circuit considerably. Factors affecting line parameters  The main factors are 1. Voltage level. 2. line length. 3. type of conductor used. 4. Number of conductors. 5. the spacing of the conductors as they are mounted on the supporting structure. Types of Conductors There are many types of cables and they include: • Aluminum Conductors; Homogeneous designs; Composite designs ; Expanded ASCR (Al Steel Core) • Steel Conductors Galvanized steel conductors with various thicknesses of zinc coatings are used. ACSR Line Resistance • The resistance of the conductor is the most important cause of power loss in a power line. Direct-current resistance is given by : ρ = resistivity of conductor, l = length , A = cross-sectional area • There are several factors that affect the value of the DC line resistance. Factors affecting line resistance 1. Conductor stranding. 2. Skin Effect : When ac flows in a conductor, the current is not distributed uni