Maintain site safety with Schneider Electric arc flash protection solutions.
An arc flash is an electrical accident that creates a high-temperature explosion. It can vaporise surrounding metal, set fires, and result in severe burns.
Although rare, arc flashes can have grave consequences, so it is important to ensure workers and sites are always protected.
An arc flash can happen during abnormal use due to corruption of isolation, or in circumstances involving animals, flooding, vibrations, or corrosion. It can also occur during commissioning or maintenance, rendering equipment unusable and forcing costly downtime.
When an arc flash takes place, high voltage current flows through ionised air between two or three live parts or between the live part and the ground.
An arc flash in the bus bar of a distribution panel is an example of the worst-case scenario. In this case, an arc flash heats up surrounding air rapidly, resulting in overpressure within the electrical panel.
An arc flash may be initiated by a component failure or over voltage, such as a lightning strike somewhere in the power system. Unfortunately, it is often the result of human error.
Arc flash prevention
Arc flashes are both dangerous and preventable. It is essential for electrical workers to understand the arc incident energy produced by a potential arc flash. Without this information, the worker cannot properly assess whether the protective equipment and clothing being used are adequate. Therefore, proper signage for arc incident energy should be in place.
If the arc flash risk cannot be eliminated, the arc incident energy is a key aspect in risk control. Energy release can have several manifestations, such as thermal radiation, pressure build-up, or shrapnel. Additionally, incident energy is responsible for potential damage to the installation and the asset.
The arc incident energy is largely determined by the fault current and fault clearance time. The shorter the fault duration, the smaller the arc incident energy. This is where fast power system protection becomes essential.
The practice of power system protection is a well-established science, and the challenges are well understood. To achieve selective protection schemes, delayed tripping is commonly used to coordinate different protection stages.
Unfortunately, using time coordination results in relatively long fault clearing times, which negatively impacts arc incident energy.
Selective protection can be achieved by using more advanced protection methods such as differential protection.
Differential protection is absolutely selective when well designed. The selective property is what makes differential protection fast, as there is no need for time-delayed coordination. However, differential protection tends to be expensive and demanding from an engineering perspective.
Dedicated arc flash protection can provide a solution for short fault clearing to reduce arc incident energy.
The most common form of arc flash protection is the detection of light emanating from the arc flash. Light-detection arc flash protection is selective by nature, so there is no need for time delay coordination. The fault can then be cleared as fast as possible because the sensor only triggers due to light from an arc flash.
Dedicated arc flash protection devices can provide a trip command as fast as two milliseconds (ms).
The actual fault clearing time depends on the circuit breaker used. Typically, the circuit breaker can clear the fault in 50–60ms. Even faster fault clearing is possible by utilising arc quenching devices together with the arc protection device.
Arc flash protection devices
Light detection technology used in arc mitigation systems can trigger safety measures that contain or extinguish the arc, thereby preventing potential damage or harm. These safety measures may include activating circuit breakers, isolating the affected circuit, or deploying specialised arc quenching devices.
By integrating light detection technology into arc mitigation systems, organisations can significantly enhance the safety of their electrical installation. Detection and isolating the energy source should take place in the shortest possible time to reduce the incident energy.
The arc flash mitigation solution can be installed in new or installed cubicles without corrupting the isolation of electrical circuits.
The design of arc mitigation solutions should consider:
- electrical installation accessibility
- electrical distribution network understanding: identify sources of energy and current flows in case of an arc fault
- understanding of selective protection deployed in the electrical distribution network.
When an arc flash fault occurs in electrical installation, the consequences can be dangerous. Schneider Electric is helping customers stay safe around electrical equipment with a range of safety solutions.
This feature appeared in the July 2024 issue of Australian Mining.
