Arc Flash Management
In optical arc mitigation , the light emitted by the arc within the enclosure builds quickly . That light can be detected by a photoelectric receptor or length of fiber optic cable , 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 in turn limits the duration of the event and hence the total energy produced . 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 . Even when current transducers are properly sized , optical arc mitigation offers an advantage in clearing time over current arc mitigation . Optical sensing can reduce clearing time and arc energy release by 50 % over current transducers . However , a current arc mitigation is preferred over having no arc mitigation components integrated into the control system . If no arc mitigation is integrated into the control system , upstream equipment with undetermined clearing time will need to be configured to respond to an arc event . Unlike the arc-resistant cabinet , arc mitigation also reduces damage to equipment ( instead of simply
redirecting the energy that escapes the cabinet ). It can function even when the doors are open and maintenance is being performed , and it does not require the heavy metal-clad cabinet with its larger footprint . For example , in the POWERSAFE™ system developed at Watlow ® for medium voltage process heaters , sensors can be placed within the thermal controller , SCR node and / or single contactor node , all of which are protected by a feeder / breaker . Up to 12 heaters may be run from a single feeder / breaker , with each heater controlled by its own hub or switching circuit node . When the sensor senses an arc flash event in any compartment , the feeder / breaker will shut down the lineup to limit damage caused by the arc .
Takeaways Again , arc flashes are well understood , and industries using medium-voltage equipment should already be aware of strategies to increase distance from such events , reduce current or decrease the duration of the event ( as well as the appropriate use of PPE ). As medium voltage process heaters become more popular in hydrocarbon processing , they too must be designed with safety in mind . Arc mitigation technologies represent the best approach here , as they actually decrease the duration of arc flash events and hence the energy released , helping to minimize the damage and risk involved . Additionally , such technologies can achieve these things with minimum footprint and project cost .
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