Transmission Line Properties and Performance

This is a pair of electrical conductors that carry electrical signals from one place to another. There are two major types of electrical signals namely; small signals and large signals. Large electrical signals carry electrical power from the generation station to the distribution center. On the other hand, small signals are used for communication purposes between devices. The post will majorly look at a large signal transmission line.

Transmission line signals


The main features of transmission line comprise the following;

  • Conductors- at least two conductors are used to carry the signal along the line. The conductor’s properties must be carefully and technically chosen to efficiently carry the signal. Aluminum and its alloys conductors are mostly used either singly or bundled.
  • Insulators- the conductors are connected only to the sending point (source) and receiving point (load). Along the path, conductors are electrically insulated from each other and from any conductive part such as support structures. Overhead conductors use air as an insulator.
  • Support structures- transmission line is mostly used, overhead conductors. To support them Pylons are erected at appropriate spans.
  • Clearance- this is the height difference between the ground and the lowest point of the conductor. It should be high enough to avoid humans, animals, or moving objects coming into contact. Tall trees should be cut below the line.


There are important features for every line that determines its performance. The key role is to effectively carry signal from source to receiving point without deration of quality or decrease of quantity. Critical parameters in electrical signals are voltage, current and frequency. To receive a signal that is exact replica of the sent one only exists in ideal world. The practical world seeks to get as close as possible to ideal. The conductor’s properties that affect the signal transmission include;

  1. Inductance- alternating current creates changing magnetic flux which in turn impedes change of current. It’s determined by the length, frequency, and material of the conductor.
  2. Resistance- this is opposition to the flow of current. Usually, it’s very small and sometimes taken as negligible. It’s determined by the length and nature of the material.
  3. Capacitance- there exist capacitance between two conductors as long as they are separated by a dielectric medium. The parameter increases with the length of conductors, conductor spacing, and nature of the dielectric medium.
  4. Conductance- since the dielectric medium is imperfect there exists a path for slam current signals to flow between them. The ability of a medium to permit the flow of electric current is referred to as conductance. It depends on the nature of the dielectric and spacing between conductors.

It’s important to note that the resistivity of a conductor carrying alternating current at high frequency is affected by the skin effect. The higher the frequency, the more the conductor charger carriers are pushed towards the surface leaving the inner part free. The resistivity increases with frequency.


We will consider four of the most important factors that are analyzed in performance of a line. This are enumerated below for your easy capture.

  • Efficiency- the sole function of a line is to transmit power is a signal from the source to the receptacle. Due to imperfection, there are power losses that are determined to assess whether they are allowable. Efficiency is the ratio of output power to input power of a line, usually given as a percentage. The higher the value, the better (means fewer losses)
  • Voltage and current limits- the amount of power transmittable is rated in terms of voltage and current. The size of the conductor determines current while insulation, spacing, and clearance determine voltage.
  • Voltage regulation- the ratio of voltage drops along the line and the voltage at the source. The lower the drop the better.
  • Propagation delay- for a very long transmission, the signal applied at the source takes an appreciable time to travel to the receiving end. The wavelength of the signal affects this delay. The shorter the wavelength the longer the delay.


A road is for automobiles, a sea line for ships and boats, a railway line for trains, and a transmission line is for the electrical signals. The line is necessitated by geographical distance separation of generation stations and load centers. You may be interested in learning more about this, feel free to engage me. What are the problems encountered in power transmission and how are they solved? That’s for you to find out.

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