What are Short Circuit Currents?
Short-Circuit Currents are currents that introduce large amounts of destructive energy in the forms of heat and magnetic force into a power system, as indicated by IEEE. IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems ( Buff Book).
Risks Associated With Short Circuit Currents?
The building/facility may not be properly protected against short-circuit currents. These currents can damage or deteriorate equipment. Improperly protected short-circuit currents can injure or kill maintenance personnel. Recently, new initiatives have been taken to require facilities to properly identify these dangerous points within the power distribution of the facility.
Advantages to Obtaining Short Circuit Analysis
Short Circuit (Fault Current) studies are required to insure that existing and new equipment ratings are adequate to withstand the available short circuit energy available at each point in the electrical system. Fault currents that exceed equipment ratings are capable of extensive equipment damage and are a serious threat to human life.
On large systems, short circuit studies are required to determine both the switchgear ratings and the relay settings. No substation equipment, motor control centers, breaker panels, etc. can be purchased without knowledge of the complete short circuit values for the entire power distribution system.
The short circuit calculations must be maintained and periodically updated to protect the equipment and the lives. It is not necessarily safe to assume that new equipment is properly rated.
Typical Analysis Report Includes:
Short circuit calculations, which highlights any equipment that is ascertained to be underrated as specified; suggested modifications to rectify the underrated equipment; (trip sizes within the same frame, the time curve characteristics of induction relays, CT ranges, etc.). The Protective Device Setting and Coordination Study is the suggested follow on analysis to develop the coordination curves, highlighting areas lacking coordination. Present a technical evaluation with a discussion of the logical compromises for best coordination.