Arc Flash Hazard Calculations
In the previous article we have discussed the definition, hazards, level of risk (read: Arc Flash: Definition, Hazards and Risks) and the causes of arc flash (read: Arc Flash Causes and Location). This article will discuss in more detail the standards and methods of calculation or how to calculate the value of the arc flash hazards or incident energy and boundary with a mathematical calculating formula developed by IEEE 1584.
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IEEE 1584 – Guide for Performing Arc-Flash Hazard Calculations
IEEE Std 1584-2018, Guide for Performing Arc-Flash Hazard Calculations, is a standard of the Institute of Electrical and Electronics Engineers that provides a method of calculating the incident energy of arc flash event.
Arc Flash Hazard calculations are currently implemented in most of the industry plants due to Safety regulations. The IEEE 1584 is an international standard that empirically derived model accurately accounts for a wide variety of setup parameters including:
- Voltages in the range of 208–15,000 V, three-phase.
- Frequencies of 50 Hz to 60 Hz.
- Bolted fault current in the range of 700–106,000 A.
- Grounded or ungrounded.
- Equipment enclosures of commonly available sizes with various conductor configurations, or open air.
- Gaps between conductors.
- Faults involving three phases.
For cases where voltage is over 15 kV or gap is outside the range of the model, the theoretically derived Lee method can be applied
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Arcing Short-Circuit Calculations
The formula or equation for estimating arcing short-circuits based on IEEE 1584-2002 is as follows:
which of:
- Ia = arcing current (kA)
- k = – 0.153 for open air and – 0.097 for arcs in a box
- Ibf = bolted short-circuit current (kA)
- V = system voltage (kV)
- G = conductor gap (mm)
Factors for Equipment and Voltage Classes
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Incident Energy Calculations
The next step is to calculate the incident energy in calories/cm2 (cal/cm2). Incident energy is defined as the amount of energy impressed on a surface at a certain distance from the source. The distance from the source is referred to as working distance.
Two equations are used for this step. The first equation is used to determine the incident energy based on a normalized working distance of 24 inches and a clearing time of 0.2 seconds. The second equation is used to adjust the normalized data to specific conditions. The clearing time is normally determined from the upstream protective device’s time current curve using the estimated arcing current.
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Arc Flash Boundary Calculations
The Arc Flash Boundary (AFB) known as Flash Hazard Boundary in IEEE 1584, is defined as an approach limit at a distance from exposed live parts within which a person could receive a second degree burn if an electrical arc flash were to occur. This boundary is typically calculated as the distance where the incident energy falls off to 1.2 cal/cm2.
Work performed within the AFB requires adequate PPE based on NFPA 70E requirements. It is always better to place the equipment in an electrically safe condition and not to perform live work.
To determine the Arc Flash Boundary
- DB = distance from arc in mm
- EB = incident energy at the arc flash boundary, typically 1.2 cal/cm2 or 5 Joules/cm2
- Ein = incident energy
- Cf = calculation factor
- t = arcing time in seconds from overcurrent device time current curve
- x = distance exponent from Table 1
- conversions: 1 inch = 25.4 mmm and 0.24 cal/cm2 = 1 Joule/cm2
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Contact Omazaki Consultant if you are looking for consultant services for studying and assessing the hazards and risks of arc flash, especially to calculate the incident energy generated by potential arc flash on your electrical system throughout Indonesia.
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Related Articles
- Arc Flash: Definition, Hazards and Risks
- Arc Flash Causes & Location
- Arc Flash Boundary and Requirements of Personal Protective Equipment (PPE)
- Arc Flash Study and Assessment
- Electric Shock Protection Study
- Power System Study and Analysis
- Short Circuit Study and Analysis
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References
- https://standards.ieee.org/standard/1584-2018.html
- https://brainfiller.com/arcflashforum/download/Arc%20Flash%20Calculation%20Guide%20Jim%20Phillips.pdf
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