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More Arc Flash Topics @ Power Better

Steps to Help Safeguard Against Arc Flash Accidents …
Promoting Worker Safety During Electrical Panel Maintenance and Upgrades

 


Brian Schmalberger, GE Industrial Solutions
April 2018  |  By Brian Schmalberger
Brian Schmalberger is an OEM segment market leader for ABB.

 

Arc flash incidents––a powerful and potentially deadly release of explosive energy, heat and sound––can often be traced to demanding operational conditions or poorly maintained systems. Factors such as worn cable insulation, dirty or corroded contacts or electrical parts, and even occasionally an ill-fated rodent, can all cause a catastrophic accident when an electrical current “arcs” between two electrical contacts.


The risk to equipment, uptime and, primarily, worker safety all create necessary caution when doing maintenance or upgrades on industrial electrical distribution and control panel equipment.


Like the residential electrician who cautiously turns off a circuit breaker before changing a light fixture, commercial facility work crews know the safest way to handle electrical maintenance and repairs is to de-energize the entire circuit or power system. That’s the recommendation OSHA makes in its electrical safety standards (1).  Yet these same OSHA standards recognize work situations where it’s not practical or possible to de-energize a circuit or electrical system before doing maintenance, repairs or upgrades. Situations where electrical circuits must remain active include the powering of:

- Life support equipment;
- Emergency alarm or security systems;
- Vital lighting or ventilation equipment;
- Live circuit or equipment testing; or
- Continuous industrial processes where production lines cannot be interrupted


Under these maintenance or repair conditions, employees may work near normally restricted or caution areas such as prescribed “arc flash,” “shock protection,” or “restricted” and “prohibited approach” boundaries. In addition, during maintenance work, personnel typically need to open protective access doors on the electrical units, further exposing themselves to active components inside the housings of motor control centers, switchboards or power panel boards. When conducting inspections or maintenance work under these active conditions, a sound combination of arc flash hazard planning, safety precautions and personnel protection, combined with employing active arc flash mitigation technology, can help safeguard employees and protect against an arc flash accident.
The following steps outline critical elements for arc flash safety that should be considered before performing maintenance or upgrades to electrical distribution equipment.


1.  Safety Planning and Arc Flash Protection

A safe arc flash program always begins with understanding the risks, and then putting together a plan with a set of procedures to avoid both technical and operational hazards. Many companies, such as ABB, work with companies to create comprehensive arc flash hazard plans, based on the guidelines of government and industry groups, including the National Fire Protection Association’s (NFPA®) 70E standard (NFPA 70-E2012, 130.3b)(1)). This and other industry standards and research define metrics for calculating potential arc flash incident energy levels and safe personnel boundary limits for workers. These standards also recommend both processes and technologies to mitigate the risk or impact of an arc flash incident.


Regulations from the National Electrical Code (NEC) and a well-executed plan also help detail the wording and placement of hazard warnings and safe boundary limits–labels that must be placed on power equipment.


Even when employing the best arc flash mitigation technology equipment and rigorously following all safety procedures, the use of personal protective equipment (PPE) provides another critical layer of worker safety. This protection, which varies according to the five ”Hazard/Risk” levels also defined by the NFPA 70E standard, begins with flame resistance (FR) clothing, safety glasses or full face shields, various hardhat standards and voltage-rated gloves, all the way up to “flash” hoods or protective “moon suits”.


2.  Active Arc Flash Mitigation

During any electrical equipment operation, but especially during system maintenance or repair, employing direct arc flash mitigation technologies offers an important line of defense. A range of technologies can be deployed to help prevent or mitigate the impact of an arc flash incident by either limiting the potential energy release or the duration of the event, or by actually rerouting or containing the arc flash energy.


Two core technologies can be employed separately or together, in various combinations, to impede the potential for arc flash accidents. These technologies work by controlling the selectivity and number of protection devices that are engaged while keeping the rest of the system powered, controlling the sensitivity and resulting speed, of a trip condition. These two technologies, instantaneous zone selective interlocking, and wave form recognition, do separate but related and supporting functions.

 

  • Instantaneous zone selective interlocking (I-ZSI) deploys multiple layers of large circuit breakers that operate as a system to protect against either small overloads or large faults. Each circuit breaker only operates when needed and acts as back-up only when necessary. I-ZSI capability provides virtually instantaneous protection selectively, regardless of the size of a power system or the main circuit breaker.
  • Wave Form Recognition (WFR) is an algorithm that instantly allows a feeder, or downstream circuit breaker (above a panel or motor control center [MCC] that has current limiting fuses or circuit breakers) to be set at very sensitive levels while still providing selectivity.  This technique provides a high level of virtually instantaneous protection where and when needed

 
Another key energy reduction technology is the use of reduced energy let-through, or RELT.  Sometimes referred to as a maintenance switch, personnel can use RELT technology to temporarily adjust the sensitivity of a trip device from 1.5 times up to 15 times the normal protection device rating, effectively controlling the duration, and severity, of an arc flash incident.


In situations when an arc flash event does occur, additional active protection systems can capture, or contain, the energy emission. Traditional arc resistant “containment” approaches rely on transferring the arc flash energy into a reinforced vessel, with the resulting heat and gas vented away from the impacted equipment.  Newer technologies, such as our Arc Vault*, employ a combination of light and current sensors to identify an arc fault signature and, via a logic controller, send a trip signal to the main breaker while triggering a plasma gun inside an absorption chamber. The plasma gun creates a low impedance, phase-to-phase path that directs the fault into a containment chamber where the arc fault energy is cooled and vented, all within eight milliseconds of the initial event.  From a maintenance vantage, it’s important to know that this technology works during arc events in either an open- or closed-door situation.


Given the risk and severity of an arc flash event on personnel and property, employing a host of design and planning protocols–aligned with both passive and active mitigation processes and technologies¬–offers industries a safer path for their workers when maintaining their electrical distribution, power control and protection systems.

     

 

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