(click for video of Arc Flash incident)

Arc-flash hazard analysis evaluates the heat released in the event of a fault in the distribution system; this fault is expected to appear as a result of user actions such as a failure in the operation of the equipment, the dropping of tools onto energized parts, or any other actions that short circuit energized parts. In the event of an arc-flash incident, the intense energy from the arc vaporizes the adjacent material that produces a sudden air expansion through the open side of the enclosure toward the maintenance worker. The energy released by the arc is function of voltage of the system, the magnitude of the current and the duration of the arc. There are four variables to consider when evaluating the energy available from an arc-flash hazard:

• The voltage and maximum short circuit current available at that point,
• The time to operate of the protective device (Or time current curve of the power fuses)
• The pick-up current of the protective device (Or TCC of the power fuses)
• Worker exposure to the Arc

The affect of the above variables is as follows:

• The combination of the maximum short circuit current and the time that the protective device takes to isolate the fault define the type of personal protective equipment (PPE) required to perform a specific work in that area.
• The pickup current of the instantaneous element is set to allow normal system operation and coordination with down stream protective devices, while reducing the arc energy to the minimum. The protective device should operate not only for bolted faults, but for faults that involved some type of impedance.
• The type of work being done defines workers exposure, for example “Reading a panel meter” since the switchgear’s door is closed requires different PPE than “Working in energized parts including voltage testing”

Arc-flash hazard analysis combines the information available from short circuit analysis and protective device coordination to optimize relay performance, having done that, details the minimum PPE required in each area based on the characteristics and environment of the task to be performed.

Standards for electrical safety in the work place require that any fault should be cleared quickly as to reduce the duration and magnitude of the heat released by the short circuit currents. New engineering practices are skewed to obtain faster fault clearing times even if that means some compromise in device coordination.

Magna Electric provides these studies and recommendations to help improve your overall power system safety. In today’s ever changing environment of electrical power distribution equipment and systems, safety and reliability are becoming the focal point of utility and industrial switchgear users. Many of these locations have upgraded their systems by converting older air circuit breakers to vacuum or by ordering new systems that are “Arc Resistant”. However, many are not aware of the opportunity to upgrade existing switchgear cubicles to arc resistant retrofits achieving optimum safety for operating personnel and reliability of installed systems. Arc Proof retrofits of existing metal clad and metal enclosed switchgear is available for lineups of most manufacturers and vintages.