Disadvantages of corona, radio interference, inductive interference between power and communication lines
Introduction
Disadvantages of corona.
Radio interference.
Inductive interference between power and communication lines
2. Introduction
Disadvantages of corona.
Radio interference.
Inductive interference between power and
communication lines
3. It has been observed that, if the spacing between two
conductors is less than their diameters, & if applied potential
between them gradually increased, a violet glow occurs round
the conductor, along with a hissing sound, at a certain value
of the potential. This phenomenon is known as corona.
The conductors have air gap between them, so air acts as a
dielectric medium. The dielectric strength of air at normal
temperature and pressure is 30kV/cm.
4. The phenomenon of violet glow, hissing noise and
production of ozone gas in an overhead transmission line is
known as corona.
For corona effect to occur effectively, two factors here are of
prime importance as mentioned below:-
1) Alternating electrical potential difference must be supplied
across the line.
2) The spacing of the conductors, must be large enough
compared to the line diameter.
5. This breakdown accompanied by following phenomenon :
Hissing noise is produced.
A faint violet glow appears which is visible in the dark.
Production of ozone gas.
Radio interference occurs.
There is a loss of power.
6. Due to corona formation, the air surrounding the conductor
becomes conducting and hence virtual diameter of the
conductor is increased. The increased diameter reduces the
electro static stress between the conductors.
Corona reduces the effect of transient produced by surges.
Effects of transients produced by lightning surges and other
causes are reduced. Charge induced on the line by surges
will be partially dissipated as a corona loss. In this way it
acts as a safety valve.
7. Corona is accompanied by a loss of energy. This affects the
transmission efficiency of the line.
Ozone is produced by corona and may cause corrosion of
the conductor due to chemical action.
Harmonics are produced in the line.
During the formation of corona, ozone gas is formed. This
gas reacts with the material of the conductors and causes
corrosion.
8. Electromagnetic interference, also called radio frequency
interference (RFI) when in the radio frequency spectrum, is a
disturbance generated by an external source that affects an
electrical circuit by electromagnetic induction, electrostatic
coupling, or conduction.
9. High voltage transmission lines and substations can cause
radio interference.
Since radio noise is associated with corona, it mainly depends
on the potential gradients at the conductors.
It is also influenced by all those factors which influence
corona, such as air density, humidity, wind contaminates,
imperfections and precipitation.
The radio noise in bad weather is about 10-25 db higher than
the radio noise during fair weather.
The radio interference is caused by electro-magnetic waves in
the frequency range of broad cast frequencies.
Radio interference : 0.5 – 1.6 MHz
By using bundled conductors, surface voltage stress, corona
and radio interference can be reduced.
10. Corona produces inductive interference between
transmission lines and wireless lines, signal.
Radio interference due to corona is of the importance for
lines above 200 kV.
The electromagnetic and the electrostatic effects mainly
depend on what is the distance between power and
communication circuits and the length of the route over
which they are parallel.
The unacceptable disturbance which is produced in the
telephone communication because of power lines is called
Telephone Interference.
11. This noise is lesser in bed weather.
Radio interference field produces by transmission line is
inversely proportional to radio frequencies.
This shows that higher frequency band service like T.V.,
frequency modulated broadcasting, microwave relay and
radars have less chance of affecting their services.
In Extra High Voltage lines the radio noise is a very
important consideration is designing a line.
12. There are various factors influencing the telephone
interference. These factors are as follows:
1) Because of harmonics in power circuit, their frequency
range and magnitudes.
2) Electromagnetic coupling between power and telephone
conductor.
3) Due to unbalance in power circuits and in telephone
circuits.
4) Type of return telephone circuit i.e. either metallic or ground
return.
5) Screening effects.
