What You Need To Know About Arc Flash

Published by Carelabs (Carelabz)

Image: Carelabz

Arc Flash is an energy release that takes place when electricity flows through the air and two live conductors causing short circuit. In a residential setting, arc flashes usually produce little more than a brief flash of light before extinguishing themselves harmlessly. In commercial or industrial setting, voltages are high, so electrical faults usually release high energy. As a result, arc flashes in data centers routinely produce powerful explosions marked by searing heat, toxic fumes, blinding light, deafening noise and massive pressure waves.

Human and Financial Repercussions of such Blasts can be Devastating
  • Injuries to employees: Without adequate protection, workers exposed to arc flash events can suffer third-degree burns, collapsed lungs, vision loss, eardrum ruptures, puncture wounds, and even death. Literally, electrical contact results in 3,600 disabling injuries annually and one workplace death every day in the U.S., according to statistics from the National Institute for Occupational Safety and Health.
  • Steep medical and insurance bills: Covering the cost of an injured employee’s medical leave after an arc flash incident can expensive. Further, businesses experienced an arc flash may difficult to get insurance and probably pay higher rates for any coverage they do acquire until they can prove proper safety measures have taken.
  • Exposure to fines and lawsuits: Any time employees would die or get injured during the job, costly lawsuits are almost sure to follow. Unless, it is important to pay fines from the Occupational Safety and Health Administration. Literally, Occupational Safety and Health Administration has known to impose fines aggregating millions of dollars after arc flash events, and has even great companies that have yet to suffer arc flashes for failure to comply arc flash safety standards.
  • Damage to equipment: Arc Flash events are likely to damage any servers, racks, networking gear and power distribution units in their immediate vicinity. Smoke condensation can cause further harm to sensitive electrical equipment at greater distances. Also, should an arc flash trigger your data center’s fire suppression system? You can complete easily with an entire room of valuable IT resources covered in water or thick flame proof foam.
  • Delays and downtime: Companies sometimes must wait for Occupational Safety and Health Administration to complete an investigation before repairing arc flash-related damage. That means organizations with inadequately redundant data centers can get through hours, days or even weeks of downtime after an arc flash event.
  • Impact on morale: Attracting and retaining qualified technicians can difficult if an arc flash incident causes current and prospective employees to view your data center as an unsafe place to work.
1.Perform a Hazard Analysis

Every Arc Flash reduction program should start by analysing risk aimed measuring how much energy an arc flash could release at various points along with power chain. Accuracy is essential with such measurements, so data centre managers who lack direct and extensive experience with arc flash incident energy assessment should always seek help from a qualified power systems engineer.

Beginning with integration of an arc Flash risk analysis, companies should take the following steps:

  • Equip data center staff with proper Personal Protective Equipment: Technicians should never come within range of a potential arc flash incident without wearing proper Personal Protective Equipment, such as flame-resistant clothing, eye protection and gloves. Personal Protective Equipment is available in different degrees of strength with different degrees of protection. Electrical engineers and fire safety professionals have developed two standards to help organizations analyse how much protection their employees need:
  • Institute of Electrical and Electronics Engineers 1584: Created by the Institute of Electrical and Electronics Engineers, one of the world’s most respected technical professional associations, Institute of Electrical and Electronics Engineers 1584 offers guidance on quantifying potential arc flash incident energy levels.
  • NFPA 70E: Produced by the National Fire Protection Association, a non-profit organization dedicated to fire, electrical, building and life safety, NFPA 70E defines thresholds for proper Personal Protective Equipment based on  severity of potential arc flash hazards. Drawing these two standards, data collected during an arc flash risk analysis, organizations can exactly analyse their risk factor, which would analyse what kind of Personal Protective Equipment their employees should wear while working in arc flash danger zones. Data centre managers should make sure that group from any vendors or third-party service who executes maintenance strategies on their server infrastructure wear exact Personal Protective Equipment at all times.
  • Post warning labels. To make sure data centre employees are always aware of potential arc flash hazards, companies should place warning labels on any piece of electrical equipment that poses an arc flash risk. They should record arc flash hazard zones on the floor so workers not wearing Personal Protective Equipment can clearly analyse how far from electrical equipment they must stand to avoid serious injury. Note that the NFPA 70E standard explicitly needs employers to post signage notifying employees of potential arc flash dangers. Organizations that ignoring this directive would dramatically increase their chances of paying serious fines and losing expensive litigation after arc flash incidents.
  • Execute an employee training program. To make sure data centre group understand arc flash dangers and know how to avoid them, be sure every existing and newly hired employee receives thorough arc flash safety training.
2.Reduce Available Fault Current

Even though it is not applicable to environments protection by fuses and electricity limiting breakers, data centers use Non-Current Limiting Breakers can decrease the risk of incident energy released during arc flashes by decreasing the amount of available fault electricity. The following four strategies can help data centers with NCLBs significantly reduce available fault current.

Operate with an open tie during maintenance: Managing two electrical feeds helps data centers to increase repetition of their power supply, and availability of their IT systems. The downside of this power architecture, however, is that it doubles the amount of current available when faults occur. In most of the situations, opening the tie between dual power feeds during maintenance strategies decreases arc flash dangers by cutting available fault current in half.

Of course, opening ties during maintenance also temporarily renders your power scheme less redundant, exposing IT equipment to heightened risk of failure. Given destructive human and financial toll arc flashes can take, most organizations trade-off worth making.

Switch to smaller kVA and/or higher impedance transformers: In the past, server power supplies commonly generated distortion that could overheat electrical transformers. To satisfy, data centers often used bigger and hence stronger transformers than their infrastructure needed. These days, most server power supplies “power factor corrected,” so they no longer pose a risk to transformers. As a result, data centers can safely use smaller transformers suiting their needs. Following such method would save money and improve arc flash safety. As a smaller transformer releases less energy during faults, lowering the scale and impact of arc flash events.

Employ High-Resistance Grounding: During ground faults, High-Resistance Grounding systems provide a path for ground current via a resistance that limits current significance. That greatly decreases the size of line-to-ground faults and associated arc flashes. High-Resistance Grounding can use on systems that service only three-phase loads. The U.S. National Electrical Code prohibits using High-Resistance Grounding on distribution systems serving loads that connected line-to-neutral, as are most servers. This limits practicality of High-Resistance Grounding system to the section of data center that powers cooling plants and other large three-phase loads.

Use current limiting reactors: Current-limiting reactors act as a bottleneck on electrical flows, restricting electricity failures. For example, low-voltage motor control centers can supply with three single phase reactors that restrict available short circuit electricity, resulting in less energy releases when errors occur.

3.Shorten Clearing Time

Just a smaller arc flashes release less energy, to do shorter ones. There are three techniques for shortening arc flash events by decreasing fault clearance times:

Utilize Zone Selective Interlocking: Zone Selective Interlocking is a security scheme that makes use of an “inhibit” signal transmitted from downstream breakers that see error to next breaker upstream. The upstream breaker analyse both the electricity failure and the inhibit signal and therefore delays tripping, allowing the downstream breaker to clear the fault. Should a fault occur between the downstream and upstream breaker, however, the downstream feeder doesn’t see the fault or send an inhibit signal to the upstream breaker. That causes the upstream breaker to bypass at any time, significantly decreasing arc flash incident energy.

Implement a bus differential scheme: These integrated zones of protection within an electrical system. If any error take place between main and feeder breakers, then the protective devices trip immediately, Resisting arc flash durations while confining arc flash damage to specific portions of your infrastructure. Bus differential systems are typically faster and more sensitive than Zone Selective Interlocking, but need further current transformers and relaying equipment. This generally makes them harder to apply and more expensive.

Deploy an Arcflash Reduction Maintenance System: An ArcFlash Reduction Maintenance System shortens faults by passing all time delays in the trip circuit at any time electricity exceeds maximal. That permits faults to clear even faster than a circuit breaker’s “instantaneous” function makes possible. Technicians must manually allow ArcFlash Reduction Maintenance System circuits before doing maintenance work and then disable them when work is complete, using familiar lockout strategies.

4.Adopt Remote Operation

Executing probably dangerous strategies casually can safeguard data center group from injuries. There are two ways to resist the number of maintenance activity, technicians must execute while in range of ArcFlash blasts:

Install remote monitoring, control and diagnostics software: Today’s sophisticated power management systems equip administrators to execute many administrative tasks remotely. They give companies to casually de-energize electrical equipment before data center staff approaches.

Use remote shaking devices: Normally, technicians should stand close to equipment, electrical connections shake and un-shaking breakers. Remote shaking devices allow operators to execute these extremely dangerous tasks from a safe distance.

5.Predict and Prevent Faults

One of the most effective ways to prevent arc flashes is to assume and ignore the conditions that cause them. The following three solutions permit data centers to spot possible ArcFlash risk before they have  chance to harm and keep group safely away from live connections.

Analyse insulation security: Deteriorating insulations is the leading cause of electrical failures. Analysing and repairing insulation before it fails could avoid arc flash explosions. Anticipative maintenance systems give warning of insulation failure in medium voltage switchgear, substations, generators, transformers and motors.

Monitor pressure junctions: Most of the electrical equipment has pressure junctions. Like, shipping splits, load lugs and compression fittings. Over time, vibration and thermal cycling can loosen these connections. When current flows through loosened connection, it cause overheating and ultimately produces an ArcFlash. Using non-conductors thermal sensors called pyrometers. Data centers can regulate pressure junctions regularly and receive advance notification of loose connections before they become very loose that they create an ArcFlash explosion.

Use infrared (IR) windows: Using contactless IR thermography technology, IR windows enable technicians to execute IR scans without removing switchgear side panels, lessening the likelihood of arc flash events caused by accidental contact with live bus.

6.Redirect Blast Energy

Equipment that directs arc flash energy away from data center group is called “arc resistant.” Arc-resistant switchgear, for example, utilizes sealed joints, top-mounted pressure relief vents, and reinforced hinges to have the energy and heat released by arc flashes and channel them by ducts to vacant area inside or outside the data center.

When all else fails, arc-resistant switchgear offers vulnerable data center employees a critical last line of defense from the explosive power of arc flash incidents. Anyhow, protective conditions said to effective only when equipment doors closed, it is important to train technicians to fasten doors safely while operating.

Source: https://carelabz.com/need-know-arc-flash/

Carelabs is authorized provider of Electrical Installation’s Study, Analysis, Inspection, and Certification services in UAE, and offer arc flash study and analysis services.

Contact Carelabs at 971 4 514 9730 or +971 55 792 1054 (Call or WhatsApp) or email at info@carelabz.com

Published by PQBlog

Electrical Engineer

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