ARC FLASH Mitigating in
process heating applications Dennis Long, chief system designer for energy and environmental technologies business unit at industrial heating technology manufacturer Watlow and how manufacturers can mitigate their risk
M
edium or high voltage equipment for industrial applications always carries prime example of a rare, but potentially fatal, situation that can be mitigated with the right technology.
As electric process heaters become a popular alternative for larger applications that it’s vital to consider how they incorporate arc
Concerns about decarbonisation, automation and safety have driven many with larger electrical alternatives. As medium voltage process heaters are relatively novel to many applications, they represent a potential new source of risk that manufacturers must recognise.
Potential risks
occurs when there is a short circuit in a system, which can be caused by a build-up of corrosion or conductive dust. If the voltage is high enough, and if there is a path to ground or a lower voltage, the resistance of the air is overcome and results in an arc. damage. As the energy release increases, the release is high enough, molten conductor metal and high-pressure plasma energy that
can escape from the cabinet, posing a risk to anyone in the vicinity.
by several factors including equipment voltage, available current and the duration of the event. While it may be practical to reduce and death makes them a great concern.
Reducing the effects
There are three main strategies for minimising the distance from the potential source of an event, reducing the available fault current and decreasing the duration of the event. All strategies can be combined to ensure maximum safety, but this is not practical when the duration of the event is the most viable largest impact on the total amount of energy released.
There are two key approaches to compare: arc-resistant cabinets and arc mitigation technologies. Arc-resistant cabinets aim to reduce exposure to arc events by encasing the system in a metal-clad cabinet with a venting system. The heated gas and pressure is redirected through a duct, reducing the energy that could potentially explode. However, a drawback lies in the fact that the cabinet must be closed for the arc-resistant cabinet to work, as many arc events occur during maintenance, when the doors are open.
Mitigation technologies Instead of redirecting the energy from the event, arc mitigation seeks to reduce the energy of the event itself by limiting its duration. This is done by detecting the arc appropriate circuit. This can be done via sensing current, referred to as current arc
30 SEPTEMBER 2023 | ELECTRONICS FOR ENGINEERS
mitigation, or sensing light, known as optical arc mitigation.
In optical arc mitigation, the light emitted by the arc within the enclosure builds quickly, which can be detected by a photoelectric receptor, even in the early stages of the event. When detected, the signal is then sent to a protective relay, which trips the breaker automatically without the need for human intervention.
One of the main advantages of this approach is that it is independent of the actual magnitude of the arcing fault current. This allows the system to detect arcing in an early stage of its development and trigger the break sooner, which limits the duration of the event and the total energy produced. On the other hand, current arc mitigation uses current transducers to sense an increase in current produced by the arc. If the transducers are not sized correctly, they may not shut the system down or may be unable to clear the event.
Arc mitigation technologies also reduce damage to equipment, as it can function even when the doors are open and maintenance is being performed. For example, in the Watlow POWERSAFE thermal system, sensors can be placed within the thermal controller, SCR node single contact or node, which are protected by a feeder. When the sensor senses an arc shuts down the lineup to limit damage caused by the arc.
Watlow
www.watlow.com
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