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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


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


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


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


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)


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


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


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


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


Battery Hazards

• Electric shock

• Lead dust toxicity

• Acid fumes

• Explosion


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


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)


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


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


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


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)


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


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


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


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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