Corona Discharge, kasinabi usab nga Corona Effect, usa ka electrical discharge phenomenon nga mahitabo kon usa ka conductor nga nagdala og mataas nga voltage ionizes ang mga surrounding fluid, kasagaran ang hangin. Ang corona effect mahitabo sa high-voltage systems kon walay sapat nga pag-atiman aron limitahan ang strength sa surrounding electric field.
Kon ang corona discharge adunay energy loss, ang mga engineers molihok aron mapugos ang corona discharge aron makamini ang electrical power loss, production of ozone gas, ug radio interference.
Ang corona discharge makapahimo og audible hissing o cracking noise tungod kay ionizes ang hangin sa palibot sa conductors. Kini common sa high-voltage electric power transmission lines. Ang corona effect makapahimo usab og violet glow, production of ozone gas sa palibot sa conductor, radio interference, ug electrical power loss.
Ang corona effect natural nga nahitabo tungod kay ang hangin dili perfect insulator—aduna'y daghang free electrons ug ions sa normal conditions. Kon ang electric field mahimo sa hangin sa pagitan sa duha ka conductors, ang free ions ug electrons sa hangin mag-experience og force. Tungod niini, ang ions ug free electrons ma-accelerate ug mobiya sa uban pa direction.
Ang charged particles sa ilang motion mag-collide sa uban ug sa slow-moving uncharged molecules. Busa ang numero sa charged particles maoas ra nga madaghan. Kon ang electric field matigas, ang dielectric breakdown sa hangin mahitabo ug arc mahimo sa pagitan sa conductors.
Electric power transmission naka-deal sa bulk transfer sa electrical energy, gikan sa generating stations nga naa sa dako nga layo gikan sa main consumption centers o cities. Tungod niini, ang long-distance transmission conductors importante aron effective power transfer—which in-evidently results in huge losses across the system.
Minimizing these energy losses has been a major challenge for power engineers. Corona discharge can significantly reduce the efficiency of EHV (Extra High Voltage) lines in power systems.
Duha ka factors importante para mahitabo ang corona discharge:
Alternating electrical potential differences must be supplied across the line.
The spacing of the conductors must be large enough compared to the line diameter.
Kon ang alternating current gibuhian sa duha ka conductors sa transmission line nga adunay spacing dako kaysa sa ilang diameters, ang hangin sa palibot sa conductors (composed of ions) subjected sa dielectric stress.
Sa low values sa supply voltage, wala mahitabo tungod kay ang stress dili matigas aron ionize ang hangin sa labas. Apan kon ang potential difference mas taas pa sa threshold value (known as the critical disruptive voltage), ang field strength mas matigas aron ang hangin sa palibot sa conductors dissociate into ions—making it conductive. This critical disruptive voltage occurs at approximately 30 kV.
Ang ionized air resulta sa electric discharge sa palibot sa conductors (tungod sa flow sa mga ions). Kini makahimo og faint luminescent glow, sama sa hissing sound accompanied by the liberation of ozone.
This phenomenon of electric discharge occurring in high-voltage transmission lines is known as the corona effect. Kon ang voltage sa lines continue to increase, ang glow ug hissing noise mas intense—inducing a high power loss into the system.
The line voltage of the conductor is the main determining factor for corona discharge in transmission lines. At low values of voltage (lesser than the critical disruptive voltage), the stress on the air is not high enough to cause dielectric breakdown—and hence no electrical discharge occurs.
With increasing voltage, the corona effect in a transmission line occurs due to the ionization of atmospheric air surrounding the conductors – it is mainly affected by the conditions of the cable as well as the physical state of the atmosphere. The main factors affecting corona discharge are:
Atmospheric Conditions
Condition of Conductors
Spacing Between Conductors
Let us look into these factors in greater detail:
The voltage gradient for the dielectric breakdown of air is directly proportional to air density. Consequently, on stormy days, the number of ions surrounding the conductor increases due to continuous airflow, making electrical discharge more likely than on clear weather days.
The voltage system must be designed to accommodate these extreme conditions.
Corona’s impact is highly dependent on the conductors and their physical condition. The phenomenon is inversely proportional to the diameter of the conductors, implying that an increase in diameter considerably reduces the corona effect.
Moreover, the presence of dirt or roughness on the conductor reduces the critical breakdown voltage, making the conductors more susceptible to corona losses. This factor is particularly significant in cities and industrial areas with high pollution, where mitigation strategies are essential to counter its negative effects on the system.
The spacing between conductors is a crucial element for corona discharge. For corona discharge to occur, the spacing between the lines should be much larger than its diameter.
However, if the spacing is excessively large, the dielectric stress on the air decreases, reducing the corona effect. If the spacing is too large, corona might not occur at all in that region of the transmission line.
Given that corona discharge invariably leads to power loss in the form of light, sound, heat, and chemical reactions, it’s crucial to employ strategies to minimize its occurrence in high-voltage networks.
Corona discharge can be reduced by:
Increasing the conductor size: A larger conductor diameter results in a decrease in the corona effect.
Increasing the distance between conductors: Increasing conductor spacing decreases the corona effect.
Using bundled conductors: Bundled conductors increase the effective diameter of the conductor – hence reducing the corona effect.
Using corona rings: Electric fields are stronger at points of sharp conductor curvature, hence corona discharge first occurs at sharp points, edges, and corners. Corona rings, which are electrically connected to the high-voltage conductor, encircle the points where the corona effect is most likely to occur. They effectively ‘round out’ the conductors, reducing the sharpness of the conductor surface, and distributing the charge over a wider area, thereby reducing corona discharge. Corona rings are used at the terminals of very high-voltage equipment (such as at the bushings of high-voltage transformers).
A closer look at the relationship between corona discharge and current reveals further insights into this phenomenon’s impact on high-voltage systems.
The flow of electric charge plays a vital role in the occurrence of corona discharge. When a high voltage is applied to a transmission line, the current flowing through the conductors creates an electric field around them.
This electric field ionizes the air molecules surrounding the conductors, leading to the corona effect.
The magnitude of the current flowing through the transmission line is proportional to the severity of corona discharge. Higher current levels generate a stronger electric field, leading to more ionization and a higher likelihood of corona discharge.
The interaction between current and corona discharge contributes significantly to power losses in transmission systems. As the current increases, the corona discharge becomes more intense, leading to more power being lost in the form of light, heat, sound, and ozone production.
