Practical Arc Flash Protection for Electrical Safety Professionals
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Transcript of Practical Arc Flash Protection for Electrical Safety Professionals
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Practical Arc Flash Protection for Electrical Safety
Professionals
Arc Flash Protection Technology Training that Workswww.idc-online.com/slideshare
Overview
• Hazards of general nature in industrial installations • Electrical hazards
– Direct and Indirect electric shock
– The deadly combination of heights and electric shock
– Hazards due to arcing/flashover
– Hazards from use of electrical equipment in explosive environment
– Hazards due to high temperature in electrical equipment
– Need for periodic inspection and maintenance for safe operation of electrical equipment
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Electrical Hazards• Electric shock and associated effects
• Injuries by electric shock combined with fall
• Arc flash causing external burns
• Explosion caused by electrical sparks
• Other thermal effects
• Hazards from electrical battery installations
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Electric Shock-Reasons
• An electric shock can happen– Due to exposure to live parts
(Direct contact)– Due to exposure to parts that
accidentally become live (Indirect contact)
• Due to potential difference in the ground under certain conditions
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Electric Shock: Effects• Causes current flow through body
• Causes muscular contraction
• Can cause stoppage of heart/breathing
• A shock is often accompanied by a fall– A non-fatal shock can result in a fatal fall– While working on electrical systems at heights, adopt
preventive measures to avoid a fall
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Burns• An electrical short circuit is accompanied by arcing• Extent of arcing depends on
– Fault energy level of the system (VA)– Time of fault clearance
• High energy faults can cause melting of components– Copper/aluminium conductors– Steel parts of enclosure– Results in deposition of toxic copper salts on the skin
• Skin burns can also be caused at the point of contact (without overt arcing)
• Internal damage due to passage of electricity (Example: Lightning current through a human body)
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Temperature Hazards
• External surfaces of electrical equipment often attain elevated temperature– Example: Bus ducts can often attain
surface temperatures of over 60 Deg C
• Exposed conducting parts can attain even higher temperatures– Example: Bus bars often run at
temperatures in excess of 100 Deg C
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Temperature Hazards
• Electrical joints/mating surfaces can have temperatures exceeding the conductor temperature
• This is because of increased localised resistance
• High surface temperature can cause ignition if flammable vapors are present in the environment
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Fire Hazard
• An external fire can often result from an electrical fault– Example: A wiring short circuit and presence of
combustible substances in the vicinity
• Certain electrical equipment contain inflammable substances and improper handling can result in fire– Example: Large transformers with mineral oil for
cooling
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Explosion Hazard• Special care for electrical equipment in hazardous atmosphere• Many electrical equipment produce arcing or sparking in normal
operation– Example: Contactors, Carbon brushes, Push buttons/switches
• Some equipment may generate arcs during abnormal conditions– Example: A terminal short circuit in a motor
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Battery Hazards
• Electric shock
• Lead dust toxicity
• Acid fumes
• Explosion
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Structure of an Electrical System• Incoming circuit• Step-down transformer• Primary distribution • In-plant generation (Primary)• Step down transformer• Secondary distribution• In-plant generation (Localised/secondary)• Local distribution centers (MCC/DBs)• Uninterrupted power supplies to specific critical loads• Loads on primary and secondary distribution system
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Main Components-1• Generation equipment-(Captive generation in
industry)
• Step-up/step-down Transformers
• Transmission lines (long distances)
• Cables (Medium distances)
• Bus ducts (Short distances)
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Main Components-2
• Distribution equipment– Isolation equipment (for safety purposes)– Bus bars– Switching equipment (circuit breakers/contactors)– Instrument transformers– Protection equipment
• Loads– Motive, Heating, Lighting
• Uninterrupted power supplies with battery
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Potential Hazards-1
• Generation equipment:– Electric shock, flash-over, mechanical hazards
• Transformers:– Electric shock, flash-over, fire hazard
• Overhead Transmission/distribution lines:– Electric shock, flash-over, fall from heights
• Cables:– Electric shock, flash-over, fire hazard
• Battery Installations:– Electric shock, toxicity, explosion/fire
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Potential Hazards-2
• Bus ducts– Electric shock, flash-over, thermal hazard
• Distribution equipment– Electric shock, flash-over, thermal hazard, fire hazard
• Motive equipment– Electric shock, flash-over, thermal hazard, mechanical hazards
• Heating equipment– Electric shock, flash-over, thermal hazard
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Potential Hazards-3
• Lighting equipment– Electric shock, flash-over, thermal hazard, fall from
heights
• Uninterrupted power supplies with battery– Electric shock, flash-over, hazards from corrosive
liquids and explosive gases, toxicity (lead, cadmium)
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Reasons for Electrical Accidents
• Failure to isolate or inadequate or insecure isolation (60%)
• Poor maintenance and faulty equipment (30%)
• Insufficient information about the system being worked on
• Carelessness and lack of safe procedures
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Summary of Safety Measures-Technical• Safe design/installation of plant and equipment• Safe operating and maintenance practices• Appropriate knowledge on the part of workers
– Training – Certification
• Warning signs at points of hazard• Use of equipment/sensors to warn incipient
problem
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Summary of Safety Measures-Procedural
• Documented procedures and instructions
• Proper periodic inspection and prompt repairs
• Use of personal safety equipment
• Avoiding live/hot work except where mandated by the relevant procedures
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Summary of Safety Measures-Organisational
• Creating an organisational safety structure to handle safety issues, lapses and accidents
• Updating documentation to reflect latest regulatory changes
• Employee training• Competence testing and certification• Create safety awareness by frequent safety
campaigns and rewarding accident-free operation
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DO YOU WANT TO KNOW MORE?
If you are interested in further training or information, please visit:
http://idc-online.com/slideshare