Electrical arc flash analysis: Calculating incident energy and arc flash boundary.
1 Answer
Electrical arc flash analysis is a critical safety assessment in electrical systems. It involves calculating two important parameters: the incident energy and the arc flash boundary. These values help determine the level of personal protective equipment (PPE) required for personnel working on or near electrical equipment.
Incident Energy (IE):
Incident Energy is the amount of thermal energy released during an electrical arc flash event and is measured in calories per square centimeter (cal/cm²) or joules per square centimeter (J/cm²). It represents the potential heat exposure to a worker at a specific distance from the arc flash source. To calculate the Incident Energy, follow these steps:
Step 1: Gather necessary data
Equipment information: Voltage, fault current, and clearing time (typically from protective devices like circuit breakers).
Working distance: The distance from the arc source to the worker's face and chest (usually 18 inches or 46 centimeters).
Step 2: Calculate the Arc Clearing Time
Determine the time it takes for the protective devices to clear the fault. This information can be obtained from coordination studies or protective device settings.
Step 3: Calculate the Incident Energy (IE)
The formula for calculating the Incident Energy (IE) is as follows:
IE (cal/cm²) = (K × I² × t) / D²
Where:
K is a constant that depends on the units used for current and distance. For imperial units (amps and inches), K = 0.00995. For metric units (amps and centimeters), K = 4.184.
I is the available fault current in amperes (A).
t is the clearing time in seconds (s).
D is the working distance in centimeters (cm).
Arc Flash Boundary (AFB):
The Arc Flash Boundary is the minimum safe distance from the arc source where the incident energy is less than a certain level (e.g., 1.2 cal/cm²). Workers must wear appropriate PPE within this boundary to protect against potential arc flash hazards.
To calculate the Arc Flash Boundary, use the following formula:
AFB (in centimeters) = 91.44 * √(IE × 4.184)
Where:
IE is the incident energy in joules per square centimeter (J/cm²).
Remember that arc flash analysis should be conducted by qualified electrical engineers or professionals who have the necessary knowledge and experience to handle electrical system assessments safely. The data used for the calculations should be accurate and up-to-date. Additionally, always adhere to the appropriate safety standards and guidelines in your region when performing an arc flash analysis.
Incident Energy (IE):
Incident Energy is the amount of thermal energy released during an electrical arc flash event and is measured in calories per square centimeter (cal/cm²) or joules per square centimeter (J/cm²). It represents the potential heat exposure to a worker at a specific distance from the arc flash source. To calculate the Incident Energy, follow these steps:
Step 1: Gather necessary data
Equipment information: Voltage, fault current, and clearing time (typically from protective devices like circuit breakers).
Working distance: The distance from the arc source to the worker's face and chest (usually 18 inches or 46 centimeters).
Step 2: Calculate the Arc Clearing Time
Determine the time it takes for the protective devices to clear the fault. This information can be obtained from coordination studies or protective device settings.
Step 3: Calculate the Incident Energy (IE)
The formula for calculating the Incident Energy (IE) is as follows:
IE (cal/cm²) = (K × I² × t) / D²
Where:
K is a constant that depends on the units used for current and distance. For imperial units (amps and inches), K = 0.00995. For metric units (amps and centimeters), K = 4.184.
I is the available fault current in amperes (A).
t is the clearing time in seconds (s).
D is the working distance in centimeters (cm).
Arc Flash Boundary (AFB):
The Arc Flash Boundary is the minimum safe distance from the arc source where the incident energy is less than a certain level (e.g., 1.2 cal/cm²). Workers must wear appropriate PPE within this boundary to protect against potential arc flash hazards.
To calculate the Arc Flash Boundary, use the following formula:
AFB (in centimeters) = 91.44 * √(IE × 4.184)
Where:
IE is the incident energy in joules per square centimeter (J/cm²).
Remember that arc flash analysis should be conducted by qualified electrical engineers or professionals who have the necessary knowledge and experience to handle electrical system assessments safely. The data used for the calculations should be accurate and up-to-date. Additionally, always adhere to the appropriate safety standards and guidelines in your region when performing an arc flash analysis.