Performance & Characteristics of Transmission Lines

Demonstrative Video

Overview

  • Lecture-16: Performance & Characteristics of TL

  • Lecture-17: Short Transmission Line

  • Lecture-18: Medium Transmission Line

  • Lecture-19: Long Transmission Line

  • Lecture-20: Surge Impedance Loading

  • Lecture-21: Ferranti Effect

  • Lecture-22: Tuned Power Lines

  • Lecture-23: Equivalent Circuit of Long TL

Objectives of this Chapter

  • Objective:

    • Develop formulas to calculate the voltage, current, and power at any point on the T/L, provided we know the values at one point, usually at one end of the line.

    • To understand the effects of parameters of the line on bus voltages and the flow of power.

    • Introduction to the study of transients on lossless lines in order to indicate how problems arise due to surges caused by lightning and switching.

Representation of Line

  • Representation of Line:

    • SHORT LINE: less than 80 Kms : capacitance neglected

    • MEDIUM LINE: 80-240 Kms

    • LONG LINE: longer than 240 Kms

  • For short and medium line: lumped parameters are used

  • Long line: Distributed parameters are used

  • Normally, TL are operated with balanced 3-\(\Phi\) load

image

  • Nomenclatures used:

\[\begin{aligned} z &= \text{series impedance per unit length per phase}\\ y &= \text{shunt admittance per unit length per phase to neutral}\\ l &= \text{length of the line}\\ Z &= zl = \text{total series impedance per phase}\\ Y &= yl = \text{total shunt admittance per phase to neutral} \end{aligned}\]

Relation between Sending end & Receiving end Quantities

$$\boxed{ \left[\begin{array}{c} V_S \\ I_S \end{array}\right]=\left[\begin{array}{ll} A & B \\ C & D \end{array}\right]\left[\begin{array}{l} V_R \\ I_R \end{array}\right] \Longrightarrow\left[\begin{array}{l} V_R \\ I_R \end{array}\right]=\left[\begin{array}{cc} D & -B \\ -C & A \end{array}\right]\left[\begin{array}{c} V_S \\ I_S \end{array}\right] }$$

Characteristics & Performance of Transmission Lines

  • \[= \text{Power sent from sending end} - \text{Line losses}\]
    Power delivered at receiving end
  • \[\dfrac{\text{Power delivered at receiving end}}{\text{Power sent from sending end}} \times 100\%\]
    Efficiency of TL
  • \[\dfrac{\text{No load receiving end voltage - F.L. receiving end voltage}}{\text{F.L. receiving end voltage}} \times 100\%\]
    % Regulation