2. What is Corona Discharge?
• Corona discharge is a process
by which a current flows in a
conductor with a
high potential into a neutral fluid,
usually air, by ionizing that fluid so
as to create a region
of plasma around the Conductor.
• The ions generated
pass charge to nearby areas of
lower potential, or recombine to
form neutral gas molecules.
• When the potential (electric field)
is large enough (33 KV =disruptive
potential gradient) the air ionizes
HV
3. • the ionized region continues to grow until it reaches
another conductor at a lower potential, a low resistance
conductive path between the two will be formed, resulting
in an electric arc, then a faint luminous glow of violet color
appears together along with hissing noise. This phenomenon is
called corona.
Welding Circuit breaker arc
real video
4. Which factors affect
Corona? Conductor:
Corona Effect is considerably affected by the shape, size and surface
conditions of the conductor. Corona Effect decreases with increases in the
size of the conductor, this effect is less for the conductors having round
conductors compared to flat conductors.
Line Voltage:
Corona Discharge effect is not present when the applied line voltages are
less. When the Voltage of the system increases corona Effect will be more.
Atmosphere:
Breakdown voltage directly proportional to the density of the atmosphere
present in between the power conductors. In a stormy weather the ions
present around the conductor is higher than normal weather condition.
Spacing between the Conductors:
Electro static stresses are reduced with increase in the spacing between
the conductors. Corona Discharge Effect takes place at much higher voltage
when the distance between the power conductors increases.
5. How to reduce Corona ?
By increasing the spacing between the conductors:
Corona Discharge Effect can be reduced by increasing the
clearance spacing between the phases of the transmission lines.
However increase in the phases results in heavier metal supports.
Cost and Space requirement increases.
By increasing the diameter of the conductor:
Diameter of the conductor can be increased to reduce the corona
discharge effect. By using hollow conductors corona discharge
effect can be improved.
By using Bundled Conductors:
By using Bundled Conductors also corona effect can be reduced
this is because bundled conductors will have much higher effective
diameter compared to the normal conductors.
By Using Corona Rings or Grading Rings:
Corona Rings or Grading Rings are present on the surge arresters to
equally distribute the potential along the Surge Arresters or
Lightning Arresters which are present near the Substation and in
the Transmission lines.
6. Advantages
Due to the corona formation,
the air surrounding the
conductor becomes conducting
and hence the virtual diameter
of the conductor is increased ,
The increased diameter
decreases the electro static
stresses between the
conductors .
Corona reduces the effects of
transients voltages.
Disadvantages
Corona is accomplished 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.
The current drawn by the line
due to corona is non-
sinusoidal and hence non-
sinusoidal voltage drop occurs
in the line ,This may cause
inductive interference with
neighboring communication
lines.
