What is an arc flash
An arc flash is a condition which is caused by the release of energy by an electrical arc, it usually occurs when an insulation or isolation between electrical conductors is breached or cannot withstand the applied voltage, it can also be caused by the movement near or contact with the equipment, or the failure of the equipment may cause a phase to ground or phase to phase fault by the arc flash incident a heavy explosion can be produced
An arcing fault is the flow of current through the air between phase conductors or phase conductor neutral and ground. it could release a large amount of radiated energy, with high temperature and a pressure blast. The arc flash will propagate through the air which produces a high-temperature plasma it will create an intense light, pressure shock wave, toxic gases, and blast fragments.
What can cause arcing faults
- Careless cover or device removal
- Misalignment of moving contacts
- Dielectric breakdown or dirt contamination
- Entry of foreign body like squirrel or snake
- It can be caused if any foreign object (tool) is dropped in the equipment
How to prevent arcing faults
- Periodic inspection and maintenance could provide the extension of equipment life and it could ensure operation efficiency
- Mechanical and electrical testing
- Cable testing, relay, and metering calibration
- Infrared testing, ATS testing/troubleshooting
- Arc-resistant switchgear can be used
- Line diagram for the electrical system must be maintained
- Protective device must be maintained according to the manufacturer’s instruction
- Maintenance of overcurrent protective devices
- Arc flash hazard analysis must be updated when a modification or renovation takes place
- Equipment must be field marked with a label which contains the available incident energy
- Improper or inadequate maintenance must not be done for the protective devices
- Training for workers
- Tools for safe work
An arc flash analysis is not required in these conditions
- If the circuit is rated at 240v or less
- If the circuit is supplied by one transformer
- If the transformer which supplies the circuit is less than 125Kv
Limits of approach
There are certain limits of approach for a person to avoid arcing impact if an arc flash occurs and these limits are shown in the above figure
Prevention of arc faults
Reducing the arcing current
If we limit the current available for faults in a protective device and then we can see the reduction in incident energy
Increasing the working distance
Increasing the working distance will reduce the incident energy, the working distance can be increased by using the remote operating devices and extension tools
By using arc flash relay
An arc fault will result in a huge amount of light, so we can use arc flash relay to detect the light it uses optical sensors to detect the rapid increase of light we can use solid state relay for a quick response
By using the fiber optic
Arc flash detection can be done by using optical fiber, a plastic fiber with glass core is routed throughout all high voltage compartments where an arc could occur it will act quickly whenever there is an arc flash, for fast tripping solid state relay is used , if the optical and the electrical system indicate an arc flash fault then the relay issues a trip signal