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ELECTRICAL SAFETY Reducing the effects
There are three main strategies for minimising 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 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 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 minimise the risk and damage involved.
Watlow
www.watlow.com
W
ELEcTRIcaL InspEcTIons In ThE oIL and gas IndusTRy
hen electrical connections and components break down unexpectedly, the result may be unplanned downtime, costly repairs,
and production loss. There is also an increased risk of fire due to electrical short- circuits or cable burning. That is why it is important to perform routine checks to ensure that the electrical distribution system is in proper working order, including inspection of busbars, circuit breakers, fuses, and switchboards. Electrical distribution boards are typically housed inside cabinet enclosures, making them difficult to inspect for impending failures. Electrical connections and components
typically show signs of overheating before they fail. Thermal imaging technology can provide key information that the eyes alone cannot detect. A thermal camera, such as the FLIR E95, can show maintenance professionals hot spots on components and connections, helping them recognise stressed
elements of an electrical installation before failure and break down. This gives them the opportunity to solve electrical issues as part of planned maintenance before it causes a serious and costly problem. Maintenance professionals can also use thermal imaging in combination with other instruments including clamp meters, digital multimeters, and IR Windows to ensure the distribution system is operating optimally. Through regular thermal inspections,
maintenance professionals can quickly detect and locate temperature issues (hot spots) on electrical components and equipment. Loose connections, bad contact, fuse issues, unbalanced loads, and stressed earth leakage can be discovered using a thermal imager. Improve safety by reducing risk of electrical fire; avoid unexpected breakdowns; reduce risk of unplanned electrical outages; and organise planned repairs and preventive maintenance.
Teledyne FLIR
www.teledyneflir.com
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