The Arc Flash Hazard Analysis identifies the levels of incident energy throughout the system.
An arc flash is the result of a rapid release of energy (light and heat) due to an arcing fault between electrical conductor(s) and another electrical conductor(s) or ground with enough electrical energy to cause damage or fire, and injury. During an arc fault air becomes the conductor. A massive amount of energy discharges during the arc flash or blast. This energy burns the conductors, vaporizing the copper and thus causing an explosive volumetric increase, the arc blast. This explosion propels deadly shrapnel and molten metal as it dissipates. This rapid release of energy can cause debilitating burns, other injuries and even death. Without an Arc-Flash Hazard Analysis, employers cannot properly protect their personnel from arc-flash.
Elements of the Hazard Analysis
- Short Circuit Study- The short circuit study calculates the maximum short circuit current the electrical power system may be subjected to at each equipment location through out the distribution network from the sources such as utilities, generators, and motors. The equipment includes substations, switchgear, motor control centers, and panels with their respective over current protective devices; generators; transforms; motors; and UPS equipment. The short circuit results determine the required ratings for electrical equipmen6t to adequately sustain the fault current capacity of the system. If a short circuit occurs, the electrical power system’s available energy is directed to the point of the fault in amounts that greatly exceed the normal operating currents, and the equipment must have the ability tow withstand and interrupt these large currents until the protective device opens to clear the faulted portion of the circuit.
- Protective Device Evaluation - The protective device evaluation study determines if the equipment ratings needed to sustain the fault currents calculated by the Short Circuit Study are adequate. Each circuit breaker, bus, etc., is reviewed in regards to the available short circuit to determine that the equipment can adequately withstand the fault current.
- The Protective Device Time Current Coordination - The protective device time current coordination study reviews the relay and circuit breaker trip settings, fuses, and their operating time and current characteristics in order to properly coordinate these settings with upstream and downstream devices so that any faults are isolated to the location of the fault; hence, limiting the impact to the remaining portions of the system. The coordination study is used in an Arc Flash study to determine the length of time an arc would occur which is directly related to the incident energy associated with an arc flash event.
What the Analysis Reveals
The Hazard Analysis will identify the locations which require PPE greater than Category 0. The review determines if there are possible arc flash mitigation recommendations that can be implemented to reduce the incident energy levels. Such recommendations might include device setting changes, replacement of molded case type circuit breakers with static trip type circuit breakers, changing fuse types, or installation of additional fused disconnects or circuit breakers. As a result of reducing the incident energy levels the corresponding Category of PPE required to work on the equipment while energized is reduced.
FOR MORE INFORMATION: Emerick Martin, PE, Senior Electrical Engineer