HEALTH & SAFETY ARC MITIGATION TECHNOLOGY
WATLOW
Mitigating arc flash events in process heating applications
Medium or high voltage equipment for industrial applications always carries certain safety risks . Arc flash events are a 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 have historically favored gas-fired heaters , it ’ s vital to consider how they incorporate arc flash mitigation features . Here , Dennis Long , chief system designer for energy and environmental technologies business unit at industrial heating technology manufacturer Watlow , shares insight into why arc flashes happen and how manufacturers can mitigate their risk .
Concerns about decarbonization , automation and safety have driven many organizations to replace gas fired heaters 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 recognize .
POTENTIAL RISKS
An arc flash is an electrical explosion that 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 .
Arc flash events can result in significant damage . As the energy release increases , the risk of fire and injury rises with it . If the energy 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 .
The potential arc flash energy is determined by several factors including equipment voltage , available current and the duration of the event . While it may be practical to reduce the potential arc flash energy while limiting voltage or current , overall project cost can make this difficult . Although arc flash incidents are rare , their potential for damage , injury and death makes them a great concern . Some estimates put the incidence of arc flash events between five to ten per day worldwide .
REDUCING THE EFFECTS
There are three main strategies for minimizing the effects of arc flashes , including increasing 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 considering overall project cost . That said , the duration of the event is the most viable influencer to reduce damage and has the 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 metalclad 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 flash early and automatically tripping the appropriate circuit . This can be done via sensing current , referred to as current arc 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 flash event in any compartment , the feeder shuts down the lineup to limit damage caused by the arc .
As medium voltage process heaters become more popular , they must be designed with safety in mind . Arc flash mitigation technologies represent the best approach here , as they decrease the duration of arc flash events and hence the energy released , helping to minimize the risk and damage involved .
For further information , please visit www . watlow . com / news
Issue 58 PECM 103