2010

UNSW ENGINEERING @ UNSW

13 Supervisor – A/Prof. Colin Grantham

Arc Flash Safety- An Industry Review

Introduction Arc flash is a major concern for many industries worldwide, but particularly the power distribution industry with workers operating on and within close proximity to live electrical assets. Arc incidents are often caused due to a fault across phases or phases to earth either from mechanical failure, protection failure or human error. Currently the Australian power distribution industry standard is cotton drill garments, insulating gloves and safety glasses when working on or near live electrical apparatus. The current standard provides no specific PPE(Personal Protective Equipment) for arc flash protection. The American IEE1854-2002 model has been shown to be fundamentally flawed and as such no reliable guideline exists for the selection and classification of PPE, safe work methods (SWM) and equipment ratings. Thesis Objectives

Data Analysis and Arc Flash Modelling The testing supported Dr Sweeting’s model that ~90% of the arc flash energy is in the plasma cloud, confirming the IEEE-1584 test method is flawed.

PPE Testing

The test rig utilised 3 parallel copper electrodes spaced 25mm apart and 500mm from the mannequin. Calorimeters measured the incident energy of each arc flash event and high speed cameras recorded each test.

Techasafe(Arc Rated) Work Shirts In comparison to cotton, the Techasafe work shirts performed extremely well and outperformed the cotton shirts in every way, most importantly they did not ignite. They withstood double the energy level before breakthrough.

Ausgrid PPE Recommendations • Procure and introduce a new workplace standard to wear

Tecasafe arc rated shirts, replacing cotton (drill and polo). • Procure and distribute Paulsen arc rated face shields as

soon as possible and progressively introduce them as part of mandatory PPE when operating within 500mm of exposed Low Voltage.

• Recall the current issue sweatbands in helmets and replace them with the woollen alternative.

• Advise against the use of non FR rated wet weather gear and issue a recall to those with the non FR reflective strip.

• Issue a safety bulletin to inform workers of the need for cotton undergarments rather than polyester.

• Issue a safety bulletin to inform workers of the changes to mandatory PPE and SWMS that are to take place.

The incident energy varied linearly with time and through applying Least Squares arrived at the following empirical model from the testing;

Incident Energy = 18.0958t + 0.16962

Conclusion The works in the thesis arrived at six distinct conclusions; • Cotton garments are completely inadequate in protecting

against an arc flash and worsens the injuries a worker sustains.

• The energy contained in the plasma cloud of an arc is around 83% of the total fault energy and as such it is vital to test PPE in a way that maximises exposure to this energy.

• Incident energy varies with a linear nature over time. • The IEEE 1584 empirical method underestimates incident

energy by up to a factor of 4 and is typically 2.85 times less. • Confirmed Dr Sweeting’s research, IEEE-1584 2002

standard is fundamentally flawed and inappropriate for the determination of PPE.

• Dr Sweeting’s NENS09 empirical model should be adopted as the Australian network standard.

The empirical model corresponded with Sweeting’s research (within 10%) and showed that the IEEE-1584 method underestimated incident energy by a factor of 2.85, while the Lee model overestimated by 2.5. Arc roots travel

through a constricted arcing column, ionising the air and carrying with it debris and superheated gasses. Slide 1 Demonstrates the importance of OAFP.

Assessor – A/Prof. Jayashri Ravishankar James Craig Moody 3289288

• Evaluate current international arc flash standards, specifically the IEEE-1584 2002, Lee Method and NENS09, and asses their validity.

• Perform world first arc flash testing alongside Ausgrid at the Lane Cove high power test centre.

• Verify the testing method against Dr Sweeting’s model in NENS09 and model the relationship between fault time and arc energy.

• Identify PPE that is unsuitable for electrical works • Make recommendations for the revision of industry

standard ENA NENS 13. • Determine the feasibility of retro-fitting OAFP (Optical

Arc Flash Protection) to electrical assets • Provide conclusions and recommendations to Ausgrid.

The prime objectives of this thesis and the testing performed at the Lane Cove Test centre with Ausgrid was to assess the performance of current issue PPE when exposed to an arc flash on parallel electrodes.

Cotton Work Shirts The testing revealed a very poor performance for cotton work shirts with all tests carried out above 2cal/cm² resulting in the breakthrough, ignition and complete burning of the shirts.