- Safety Corner | August 14, 2018
Technologies Advancing Incident Energy Reduction
Technological advancements have changed the landscape when it comes to incident energy and arc flash problems in the industry. In the 1970s, the industry had ground-fault protection equipment (GFPE), the latest in electrical safety technology for the times. Since then, the integration of electronics and overcurrent protective devices (OCPD) has brought forth even more capabilities from which both owners and electrical workers can benefit. The arc quenching technologies on the market today, also referred to as active arc flash mitigation systems, have taken arc flash reduction to a whole new level. It is important for us to be aware of technological advancements to ensure the solutions employed on projects are the latest available for the safety of electrical workers and the reliability of the electrical distribution system. These technologies can not only save lives but also a lot of money for owners.
Time and Current
The amount of incident energy at any given point in the power distribution system is a matter of the amount of available fault current and the amount of time that fault current is permitted to flow. The control of the amount of time that current is permitted to flow within a circuit has historically been left to the performance of the overcurrent protective device alone, whether it be a fuse or a circuit breaker. Overcurrent protective devices can only detect current for interruption. Some arc flash reduction systems come in the form of relays that trigger the opening of an upstream overcurrent protective device based upon current flow. The bottom line is the faster the opening time, the lower the incident energy.
Quenching Technologies vs. Others
Recently, technology has entered the market that does not rely upon the clearing time of the upstream overcurrent protective device to limit incident energy. These systems are called quenching systems, as they create a lower impedance current path, located within a controlled compartment, causing the arcing fault to transfer its energy to this new lower impedance current path. An arc flash relay that looks at current and light is used to detect the ignition of an arcing fault using two main parameters instead of only one. Upon detection of an arcing fault, the arc flash relay simultaneously sends a trip signal to the main circuit breaker and a trigger signal to the arc fault quenching equipment. The arcing fault quenching equipment commutates the arcing fault in sub-cycle times, some systems in less than three milliseconds. This arc transfer time is an order of magnitude faster than the clearing time of a power circuit breaker and thus results in an order of magnitude reduction in incident energy.
When the latest evolution of arc quenching systems is used, known as current limiting arc fault quenching systems, the technology causes the arcing fault to transfer to a controlled compartment and significantly reduces the peak fault current, at least 25% less. Peak current reductions translate into lower electromechanical forces and therefore less stress on the power distribution system that has to carry the fault current. Since electromechanical forces are related by the square of the current, current limiting arc fault quenching systems can reduce system stress by at least 44% during a quenching operation. Less stress on the power distribution system means less wear and tear and can translate into longer life of the equipment.
Characteristics of an Arc Flash
An arc flash event is comprised of standard characteristics that make them detectable by sensing equipment. To understand how the arc quenching technologies function, we must understand the most common characteristics of