IEC evaluated Units GT1 & GT2 electrical systems from the point of interconnection with the grid to the 480V motor control centers. The detailed arc flash calculations were generated using SKM Power Tools version 18.104.22.168 modeling software. Equipment data and settings for the plant modeling were collected and supplied by plant personnel. Short circuit currents were calculated at the 34KV, 13.8KV, 2.4KV, and 480V buses and then used to calculate the arc flash energy and boundary at the various bus voltages. The duration of the arc flash current was based on existing fuses, breakers and relays settings.
The results of the arc flash study were provided in a complete report to the client. The report identified hazard potential according to the arc flash regulations of NFPA 70E (Standard for Electrical Safety in the Workplace) and IEEE 1584 (Guide for Performing Arc-Flash Hazard Calculations). The results detailed requirements for the proper Personal Protective Equipment (PPE) that must be worn by qualified personnel to operate and work on live electrical equipment. The report also included: Bus Summary Report (lists all system buses and only protective devices limiting fault to that bus); Bus Detail Report (lists system buses, protective devices and calculation outputs for all circuits); Bus Detail Table (summarizes details of each bus into a table); Bus Arc Flash Safety Label (provides labels formatted for printing onto self adhesive label paper and attaching to bus enclosures; Personal Protective Equipment Table (summarizes PPE levels and clothing requirements); Work Permit (sample work permits to be incorporated into the plants maintenance and safety program; and Single Line (the single line developed and used to model the plant. It also shows directionality and magnitudes of the Single Line to Ground (SLG) and 3 Phase (3P) short circuit currents (Isc).
IEC also recommended several next steps to the City of Pasadena to consider as a result of the study. Recommendations included installation of arc flash labels, incorporation of arc flash study results into existing plant electrical operating and safety procedures, ensuring proper personnel protective equipment is available to trained personnel, and ensuring arc flash study results are incorporated into the plant training program. IEC also recommended reviewing the plants protection scheme, performing a protection coordination study, and revising protection equipment settings to decrease the potential arc flash incident energy.