Introduction: Alternating Current Transmission Line

AC System Disadvantages

Introduction: Alternating Current Transmission Line

Alternating Current Transmission Line is the massive interconnected network with very high voltage level. The advantage of having higher voltage is to reduced the losses of grid. Electrical energy is transported from generating station to their loads through a over head line and underground cable. The importance consideration in the operation of the transmission lines are voltage drop and power loss occurring in the line and efficiency of transmission. The performance of a transmission line is governed by its four parameters.

Series Resistance:-

The resistance R is due to the fast that every conductor offers opposition to the flow of current.

Inductance ‘L’ :-

The inductance L is due to the fact that the current carrying conductor is surrounded by the magnetic lines of force.

Shunt Capacitor :-

The capacitance is due to the potential difference between the conductor of the transmission line causes the conductor to be charge and this effect will be produce charging current.

Shunt Conductance:-

It is neglected for overhead transmission line.

The resistance and inductance in series form impedance, i.e Z = R + JXι

The capacitance and shunt conductance form shunt admittance, i.e Y=JBC=JwC

The Characteristic impedance can be expressed as

Zc=√Z/Y =√(R+JXι)/JwC

If we neglected Resistance. Then Zc=√JwL/JwC =√L/C

This Zc is commonly known as Surge impedance.

The power deliver by the transmission line when it is terminated by its surge impedance is known as surge impedance load (SIL)

SIL=( Vι)2(rated) /Zc

  1. When the loading of the line is heavier then Surge Impedance Line. The voltage will be decreasing along the line. This implies that reactive power generated from the line charging is less then reactive  power consumption i.e. Transmission line act as inductance.
  2. When the loading of the Transmission line is light, less the Surge Impedance Line, the line reactive charging is greater then line reactive consumption. Then, transmission line act like a capacitance and the voltage along the line will be increasing.
  3. The voltage profile along the line is the same when the loading of the line is at its Surge Impedance Line.

Since, Based on length of line, the transmission line is classified as:

  1. Short- Transmission Line (<180 Km)
  2. Medium- Transmission Line ( 80 km – 250 km )
  3. Long- Transmission Line ( > 250 km )

AC transmission line + DC transmission line + Short Transmission Line + Medium Transmission Line + Long Transmission Line + Surge Impedance line + Resistance characteristics + Capacitor characteristics + Inductance characteristics + T-Model short Transmission Line + Π- Model short Transmission Line + Alternating Current Transmission Line + Short Alternating Current Transmission Line + Long Alternating Current Transmission Line + Medium Alternating Current Transmission Line