Short Circuit, Coordination and Arc Flash Analysis are three integral parts of electrical system maintenance and reliability. Numerous concerns may arise regarding how to maintain your electrical systems in order to optimize each piece of equipment, such as:
- Staff or contractors working on or operating live equipment without proper Personnel Protective Equipment (PPE) because available incident energy values data is unavailable and thus not marked on equipment
- System was not properly coordinated causing nuisance tripping of protective devices and in some cases, resulting in major power disruption to critical and life safety equipment
- Short circuit faults resulting in equipment damages due to inadequate bus bracing
NEC Article 110.16 states electrical equipment that is likely to require examination, adjustment, servicing or maintenance while energized shall be field-marked to warn qualified persons of potential electric arc flash hazards. This can be achieved by performing an Arc Flash Hazard Analysis and installing arc flash labels on the field equipment.
Short Circuit Analysis
The purpose of the Short Circuit Analysis is to determine the available fault current at each bus in the electrical power system, and compare the calculated values with the interrupting or withstand rating of the faulted buses. A comparison between the two values determines whether the equipment is adequately rated.
The purpose of the Coordination Analysis is to evaluate the adequacy of the protection provided for the components of the system (such as cables and transformers) and to develop recommendations for settings of the protective devices to improve the selectivity of the distribution system. A properly coordinated power system assures that system components are protected in the required manner and that protective devices operate to isolate an abnormal condition by interrupting a minimum portion of the system. A system exhibiting the latter characteristic is said to operate selectively.
An arc flash is the result of a rapid release of electrical energy into the surroundings due to an arcing fault originating from electrical equipment. Electrical systems with operating voltages exceeding 120V are susceptible to arc faults. The fault condition may be initiated by something creating a path of conductivity or by a system failure such as the deterioration of the electrical insulation. The cause of the fault quickly dissipates during the initial flash then the arcing fault is sustained by the formation of highly conductive plasma. The plasma transfers as much energy as is available and is only limited by the impedance of the arc.
Arc Flash Analysis
The purpose of an Arc Flash Analysis is to determine the incident energy available at every bus in the distribution system. The results of both the Short Circuit Analysis and Coordination Analysis are utilized to prepare the arc flash calculations. This incident energy calculation is then used to determine the PPE value for personnel that may work on this equipment while it is energized. The intent of this calculation is to create and install labels on the equipment that display the calculated incident energy and PPE recommendations at that respective equipment. These PPE recommendations should be considered when service personnel are performing maintenance on the energized equipment.