Читать книгу Arc Flash Hazard Analysis and Mitigation - J. C. Das - Страница 17

The electrical arc is recognized as high-level heat source. The temperatures at the metal terminals are high, reliably reported to be 20,000 K (35,000°F). The special types of arcs can reach 50,000 K (about 90,000°F). The only higher temperature source known on earth is the laser, which can produce 100,000 K. The intermediate (plasma) part of the arc, that is, the portion away from the terminals, is reported as having a temperature of 13,000 K.

In a bolted three-phase fault, there is no arc, so little heat will be generated. If there is some resistance at the fault point, temperature could rise to the melting and boiling point of the metal, and an arc could be started. The longer the arc becomes, the more of the system voltage it consumes. Consequently, less voltage is available to overcome supply impedance and the total current decreases.

Human body can exist only in a narrow temperature range that is close to normal blood temperature, around 97.7°F. Studies show that at skin temperature as low as 44°C (110°F), the body temperature equilibrium starts breaking down in about 6 hours. Cell damage can occur beyond 6 hours. At 158°F, only a 1-second duration is required to cause total cell destruction.