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AC and DC Arc Hazard Analysis

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Project Objective

A company that owns and operates transportation vehicles and infrastructure in British Columbia requested an arc flash hazard analysis at its facilities. Arc hazard assessment is a safety analysis dedicated to protecting personnel from incident energy released from accidental arcs.

Upon the completion of the study requested, the company would have information on the Personal Protective Equipment (PPE) required by personnel when conducting live work at the equipment. The study would also specify the arc flash boundary distance for workers to stay outside of when not dressed in the PPE indicated. 

Arc hazard assessments are mandated by many safety standards bodies such as NFPA, OSHA, and CSA. They clearly state that it is the employers’ responsibility to ensure that the workers are provided with appropriate PPE.

Kinectrics is one of the few companies—if not the only one—that has laboratory-backed results for DC arc hazard equations.

Scope of Work

Kinectrics was awarded a contract to conduct both AC and DC arc hazard analysis at the company’s distribution system and stations.  The AC components are 12.5 kV and the DC components are 600 V.
At that time, no DC arc hazard incident energy equations existed; hence, as a part of the scope of work, Kinectrics had to conduct laboratory testing and derive equations to accurately predict incident energy levels released from DC arcs.
Work performed
Kinectrics performed site visits to gather field data such as the following:
  • Transformer sizes, voltages and impedances
  • Cable types, sizes and lengths
  • Rectifier specifications
  • Protective devices’ continuous ratings and various settings
Subsequently, Kinectrics modelled the circuits and determined a laboratory testing plan to ensure that the tests would reflect the actual working conditions.
For the tests, the following parameters were varied:
  • Fault currents
  • Fault durations
  • Arc gap distances (distances between electrodes)
  • Working distances (distances measured from the electrodes to the head/chest of the personnel)
  • Direction of the electrodes (pointing out vs. pointing down)
  • Open-air / enclosed arcs (switchgear/panel boards/open-air conductors and cables)
  • Kinectrics performed almost seventy tests and derived formula to determine arcing fault currents as well as incident energy released from DC arcs.
The client company’s facility is normally fed by BC Hydro, but under emergency circumstances, power can be supplied by other sources. Instead of installing multiple labels on the equipment door, which could create confusion, Kinectrics recommended only one label be placed on the equipment, capturing the worst case scenario.
Results and Client Benefits
In most situations, the upstream protective devices were able to clear the faults instantaneously; as a result, the incident energy levels were relatively low (< 8 cal/cm2).  However, in some other situations, fault currents were low such that they could not be detected by the upstream protective devices within their instantaneous protective zones.  For this reason, high fault clearing times and hence, high incident energy levels resulted.

On completion of the study, the company had acquired the knowledge to mandate appropriate Personal Protective Equipment to personnel when live work is being performed at each of the component locations. With the correct PPE specified and utilized, the theory holds that personnel would then face minimal chance of sustaining incurable burns; and at the same time, the employer would remain unlikely to incur hefty penalties and medical bills.

Kinectrics also provided possible arc hazard mitigation measures and tools that can be used to reduce incident energy levels such as the following:

  • Light point sensors and fiber optics
  • Breakers and relays with maintenance mode
  • Arc suppression blankets
  • Arc flash barriers
  • Arc resistive switchgear
  • Modification of company’s work practices and procedures