An arc light refers to the heat and light that is produced from an electric arc that is supplied adequate electrical energy. The electrical energy is capable of causing substantial damage, injury or fire. The electrical arc goes through an increase in negative resistance leading to a decrease in the electrical resistance accompanied by an increase in the arcs temperatures. The temperatures can go beyond 19,000 degree Celsius according to arcflash.ie. The event can produce large amounts of dangerous energy resulting in the ionization of the air. Arc flash can result from many factors as discussed below. Some of the factors that may lead to an arc flash include an accidental contact, contamination or tracking over insulated surfaces, and corrosion of the surface among many other factors.
The arc formation usually goes through phases described below:
- The compression phase: the release of the energy results in the heating of the air surrounding the system. The volume of air remaining inside the cubicle becomes heated through convection and radiation. At the initial stages, temperatures and pressure vary from one region to another.
- The Expansion phase: at this juncture, a hole is formed through which superheated air escapes into the atmosphere. The process is experienced right from the first instant of internal pressure. The pressure rises to its maximum value and then it starts decreasing as a result of the hot air release.
- The Emission Phase: overpressure experienced in the system results in the ejection of all the superheated air due to the continued contribution of energy by the arc.
- The thermal phase: when all the superheated air has been ejected from the system, the system’s inner temperature nears that of the electrical arc. The final stage lasts until the arc has been quenched, after all, the metals together with the insulating materials have come into contact. An erosion of the switchgear results leading to the production of molten material, gas, and fumes.
The faults that are likely to occur in the electrical equipment are mainly of two types; these include the phase-to-ground fault and the phase-to-phase fault. Both types of defects may result from an accidental contact with a person or a tool with the active parts.
Physical effects of an arc flash may include:
- A pressure wave may occur in the environment where the arc is generated.
- Heating of the materials that may come into contact with the arc flash.
- Potentially dangerous and harmful light and sound may be produced.
Personnel hazards that may result from an arc flash may include:
- Burns; this may be caused by the high temperatures gasses released by the electrical arc.
- Expulsion of incandescent metal particles may also result in burns.
- Ejected materials may also produce injuries to most sensitive organs of the body such as eyes. Sharp materials may penetrate the cornea leading to severe injuries to the eye.
- Gasses may also cause injuries to the mucosa such as to the retina or the cornea.
- Hearing loss may result from the bad sound.
- Inhalation of toxic gasses may cause problems to the respiratory system.
- Common causes of arc flash:
- Carelessness.Carelessness is the most predominant cause of arc flash. Neglect may result from distractions, weariness, or pressure to restore the power shortage. These factors may cause one to work unprotected not follow the standard operating procedure while working on the power shortage. Carelessness may also cause one to use a faulty operating equipment producing a hazard while working.• Worn out or broken conductor insulation.
An arc flash occurs whenever there is a loss of insulation between two conductive objects. High power electrical equipment has high short circuit power hence leading to a high energy associated with the electrical arc in the case of a fault. The energy released by the arc as a result of the arc leads to increased temperatures and pressure in the surrounding system. As a result, mechanical and thermal stress is experienced in the nearby equipment, thus, leading to a potential for serious injuries. High power electrical equipment such as transformers and service entrance generators are the ones mostly associated with these occurrences.
- Exposed live parts may cause injuries when an individual or an operating equipment comes into contact with it.
- Improperly maintained switches and circuit breakers.
- Liquids such as water in touch with the electrical circuit.