Corona
Content
CORONA, SAG AND CONDUCTOR VIBRATION Batch IX
CORONA
The phenomenon of violet glow, hissing noise and production of ozone gas in an overhead transmission line is known as ¶corona· When the applied voltage exceeds a certain value called critical disruptive voltage the conductors are surrounded by a faint violet glow called corona
APPEARANCE OF CONDUCTORS
Polished and smooth conductors will have
uniform glow throughout the length of the conductors but rougher points will appear brighter.
In case of dc positive conductor will have uniform glow whereas the negative conductors has a spotty glow.
THEORY OF CORONA FORMA TION
Under normal conditions the air around the
conductors contains some ionised particles(free electrons and +ve ions)and neutral molecules. When potential difference is applied b/w the conductors , potential gradient is set up in the air which will have maximum value at the conductor surfaces. When Pot. grad . reaches 30kV per cm the velocity of free electron will be sufficient to strike a neutral molecule and produces one or more electrons. This process produces large no of ions and electrons leading to corona or spark between conductors.
FACTORS AFFECTING CORONA 1.
Atmosphere : ionisation of air ² corona. Stormy weather-ions more than normal-
increased corona. 2.
Conductor size: rough and irregular
conductor- more corona 3.
4.
Spacing between conductors: larger
distance between the conductors-reduces reduced corona. electrostatic stresses ² lower Line voltage: lower line voltage ² corona. increased voltage-increased electrostatic air around conductor is conducting stress ² increased corona.
TION CONDUCTOR VIBRA
Wind
exerts pressure on the exposed surface of the conductor . If the wind velocity is small the swinging of conductors is harmless provided the clearance is sufficiently large so that conductors do not approach within the sparking distance of each other.
Dancing occurs by action of strong wind leading to kite like movement of whole span.
Harmful
Dampers are used for protection.
effect of this occurs at the clamps or supports where fatigue or breakage of wire occur.
CORONA
The phenomenon of violet glow, hissing noise and production of ozone gas in an overhead transmission line is known as ¶corona· When the applied voltage exceeds a certain value called critical disruptive voltage the conductors are surrounded by a faint violet glow called corona
APPEARANCE OF CONDUCTORS
Polished and smooth conductors will have
uniform glow throughout the length of the conductors but rougher points will appear brighter.
In case of dc positive conductor will have uniform glow whereas the negative conductors has a spotty glow.
THEORY OF CORONA FORMA TION
Under normal conditions the air around the
conductors contains some ionised particles(free electrons and +ve ions)and neutral molecules. When potential difference is applied b/w the conductors , potential gradient is set up in the air which will have maximum value at the conductor surfaces. When Pot. grad . reaches 30kV per cm the velocity of free electron will be sufficient to strike a neutral molecule and produces one or more electrons. This process produces large no of ions and electrons leading to corona or spark between conductors.
FACTORS AFFECTING CORONA 1.
Atmosphere : ionisation of air ² corona. Stormy weather-ions more than normal-
increased corona. 2.
Conductor size: rough and irregular
conductor- more corona 3.
4.
Spacing between conductors: larger
distance between the conductors-reduces reduced corona. electrostatic stresses ² lower Line voltage: lower line voltage ² corona. increased voltage-increased electrostatic air around conductor is conducting stress ² increased corona.
TION CONDUCTOR VIBRA
Wind
exerts pressure on the exposed surface of the conductor . If the wind velocity is small the swinging of conductors is harmless provided the clearance is sufficiently large so that conductors do not approach within the sparking distance of each other.
Dancing occurs by action of strong wind leading to kite like movement of whole span.
Harmful
Dampers are used for protection.
effect of this occurs at the clamps or supports where fatigue or breakage of wire occur.
