|  | Public Health Safety | Environmental Health

The Effects of the Dissipation Factor on Corona

The velocity of random ion movement is increased by high electric field intensities. Coronas are formed when neutral molecules lose electrons upon collision with fast moving ions, creating ion pairs of opposite charges. This is called ionization by collision. Coronas occur in electrical equipment and high-voltage transmission lines, causing malfunction.

  1. Effects of Corona

    • Coronas pose a major industrial and environmental problem. In aerial transmission lines, coronas increase the chances of power loss, thus reducing transmission efficiency. The effect of coronas also shorten the lifespan of dielectric material. In air, corona stimulates the production of greenhouse gases such as ozone and nitrogen oxides. Coronas also induce radio interference.

    Preventing Corona

    • Insulation, usually under hydrostatic pressure, protects against corona formation. Stator bars form part of the insulation system used to prevent coronas in transmission lines and other high-voltage equipment such as underground cables. Oil is used to insulate transformers, and serves additional purposes such as reducing thermal resistance and increasing dielectric strength.

    Dissipation Factor

    • The dielectric dissipation factor is also referred to as tan delta. It is used to express stator bar loss including solid loss such as dielectric absorption and conductivity, and ionization loss. Dissipation factor is measured at two voltage levels. The lower level is generally below the discharge inception voltage of the stator bar but high enough to stimulate dielectric loss. The higher level is located close to the service voltage of the stator bar.

    Effect on Corona

    • The dissipation factor of commercial dielectrics is generally constant at a known temperature and voltages over the normal range of operation, provided corona is not present. However, a high dissipation factor is representative of an increase in electric field intensity, which ultimately leads to corona formation. Thus, the dissipation factor is directly proportional to corona formation and is used as a marker for it presence.

Environmental Health - Related Articles