Protection coordination studies and arc flash hazard analyses are both essential for electrical safety. While they serve different technical purposes, they depend on each other’s results and should be performed in a coordinated manner to provide a comprehensive and valid understanding of fault conditions. Each study addresses fundamentally different hazards and must be performed to ensure equipment protection, maintain system reliability, and ensure personnel safety.
The key difference lies in how fault currents are analyzed—specifically, bolted fault current versus arcing fault current. Bolted fault current refers to the maximum or minimum prospective short-circuit current during a solid (three-phase) fault. In contrast, arcing fault current flows through an electric arc plasma, which has a non-linear and dynamic impedance greater than metallic conductors. As a result, arcing fault current is generally lower than the corresponding bolted (prospective) fault current, but the ratio can vary widely (reported to range from 35%-95% of bolted fault current*) dependent mainly on system voltage and prospective fault levels; therefore it should be calculated using IEEE 1584 ** (including its arcing-current variation approach) rather than assumed as a fixed percentage.
When conducting a protection coordination study, engineers routinely perform a short-circuit analysis for various fault types—three-phase, line-to-ground, line-to-line, and line-to-line-to-ground—to inform the grading and coordination of protective devices. Because protection coordination and arc flash hazard analyzes address distinct aspects of system safety, relying on only one to represent both can result in incomplete protection strategies, non-compliance with standards, and an increased risk of equipment failure or serious injury.
But here’s the question: Why don’t we also consider arcing current in this process, especially when it can significantly differ from bolted fault current?
As engineers, can we confidently say that our protection coordination studies fully ensure equipment safety, system reliability, and personnel protection without accounting for arcing current?
Benefits of Considering Arcing Current in Protection Coordination Studies
Incorporating arcing current into protection coordination studies offers several critical advantages:
Improved Device Coordination and Faster Fault Clearing
Protective devices may respond differently under arcing fault conditions than under bolted fault conditions. By incorporating arcing current into the coordination study this ensures that relays and breakers will operate in the shortest practical time and coordinate better during real world fault current conditions. Faster, more selective, and predictable fault clearing — enabled by considering arcing current — can significantly reduce thermal and mechanical stress or damage to electrical equipment, extending its lifespan, reducing nuisance trips and downtime.
Improved Arc Flash Hazard Analysis
Arc flash studies rely on accurate arcing current values to calculate incident energy and determine appropriate PPE levels. Integrating this data into coordination studies ensures consistency and reliability across both analyses.
Arc-flash hazards arising from arcing faults can result in severe injuries or fatalities. By accounting for arcing current, engineers can more accurately assess fault-clearing times and incident energy exposure risk. This information allows engineers to determine protection system improvements using various methods and technologies, which, when implemented and combined with safe work practices, can significantly reduce risk to electrical workers.
PSC’s Expertise in Protection Coordination & Arc Flash Hazard Analysis
PSC has extensive experience in conducting protection grading studies and Arc Flash hazard analysis. We support our clients throughout the entire process—from the initial data collection of electrical networks to the final stage of arc flash label installation. Our team possesses in-depth knowledge of key industry standards, including:
- IEEE 1584 – Guide for Performing Arc-Flash Hazard Calculations
- NFPA 70E – Standard for Electrical Safety in the Workplace
- *The Electricity at Work Regulations 1989
This expertise ensures that operational personnel remain safe and compliant with regulatory requirements.
PSC also specializes in calculating relay settings and performing protection grading studies to ensure that, in the event of a fault, only the necessary parts of the system are isolated. This targeted protection approach safeguards both the plant and the network while ensuring compliance with relevant grid code requirements.
In the aftermath of a fault, PSC can carry out detailed fault investigations, analyzing system records to determine the root cause and providing actionable recommendations to prevent future occurrences.
References
*H. W. Tinsley, M. Hodder and A. M. Graham, “Arc flash hazard calculations,” in IEEE Industry Applications Magazine, vol. 13, no. 1, pp. 58-64, Jan.-Feb. 2007
** IEEE Guide for Performing Arc-Flash Hazard Calculations,” in IEEE Std 1584-2018 (Revision of IEEE Std 1584-2002), vol., no., pp.1-134, 30 Nov. 2018
How PSC can help
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