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Transformer protection schemes commonly use percentage restrained differential elements for winding protection, often delayed or desensitized by 2nd and 4th harmonic elements during inrush of LV and MV transformer banks. Differential relays are now commonly applied to smaller transformers and the zone of protection can now include cables, bus duct, circuit breakers, and other components. Harmonic controlled differential relays are seeing wider use for arc flash mitigation, and other harmonic-controlled schemes have also been proposed. Preliminary observations suggest that the harmonic spectra of arcing fault currents can differ substantially, which begs the question - when can harmonic-supervised protection be employed with harmonic restraints set to avoid operation for inrush while still operating quickly for arcing faults? This paper explores this topic by analyzing relay responses to real arcing faults using relays from multiple vendors that employ different harmonic detection algorithms.

This paper provides a follow-up to the paper The Effects of System Grounding, Bus Insulation and Probability on Arc Flash Hazard Reduction—The Missing Links . In that paper, system grounding and bus insulation were considered a means of reducing the probability of an arc flash incident by approximately two orders of magnitude. In September 2013, additional testing was conducted on a low-voltage motor control center (LVMCC) with the expectation that engineering enhancements such as insulated vertical bus, high resistance grounding, and other techniques could be implemented to further reduce the probability of an arc flash incident. The testing performed was with faults initiated in locations typically found in operating petrochemical facilities, in LVMCCs, with the starter unit door open. This paper discusses the findings of testing on real-world electrical equipment in an effort to further understand and minimize the probability of an arc flash incident. This paper reviews the physics of the arcing fault and how ignition wire, geometry, and the number of anode/cathode pairs all contribute to arcing fault energy and personnel exposure.

This paper develops a practical, cost-effective method of retrofitting existing low voltage motor control centers to reduce the arc flash energy for open door work to a much safer level. These self-extinguishing solutions are designed to reduce the arc flash energy from a calculated value in excess of 40 calories per square centimeter (cal/cm2) at an 18 inch working distance to an average tested value of less than 1 cal/cm2. The research presented focuses on the low voltage motor control center where technicians perform troubleshooting tasks on a daily basis with the motor starter door open and the circuit energized. The paper discusses engineered and tested modifications that will greatly improve the safety of the low voltage motor control center with little procedural change for the technician in the field. These solutions allow the process owner the option of upgrading existing equipment to extend the operating life of the equipment while addressing safety issues and reducing mean time to repair.

This paper provides a follow-up to the paper The Effects of System Grounding, Bus Insulation and Probability on Arc Flash Hazard Reduction—The Missing Links . In that paper, system grounding and bus insulation were considered a means of reducing the probability of an arc flash incident by approximately two orders of magnitude. In September 2013, additional testing was conducted on a low-voltage motor control center (LVMCC) with the expectation that engineering enhancements such as insulated vertical bus, high resistance grounding, and other techniques could be implemented to further reduce the probability of an arc flash incident. The testing performed was with faults initiated in locations typically found in operating petrochemical facilities, in LVMCCs, with the starter unit door open. This paper discusses the findings of testing on real-world electrical equipment in an effort to further understand and minimize the probability of an arc flash incident. This paper reviews the physics of the arcing fault and how ignition wire, geometry, and the number of anode/cathode pairs all contribute to arcing fault energy and personnel exposure.