Corona Effect in Transmission Lines
Corona Effect
in transmission lines
Presented to Dr. Amlak
1
What is Corona Discharge? Corona discharge is a process by which
a current flows in a conductor with a highpotentialinto a neutral
fluid, usually air, byionizing that fluid so as to create a region
ofplasmaaround the Conductor.The ions generated passchargeto 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 (1 Cm) and it
becomes conductive.
HV
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 anelectric arc, then a
faint luminous glow of violet color appears together along with
hissing noise. This phenomenon is called corona.
WeldingCircuit breaker arcreal videoApplicationOf electric
arc
Problem?!!
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.
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.
AdvantagesDue 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.
DisadvantagesCorona 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.
PresentersAbdallah Saied RahmyEhab Mohamed AttiaMohamed
IbrahimAhmed Abd El-Aziz
Thanks!
