Practical Arc Flash Protection for Electrical Safety Professionals

Practical Arc Flash Protection
for Electrical Safety
Professionals
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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
Technology Training that Works www.idc-online.com/slideshare
Arc Flash Protection
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

DO YOU WANT TO KNOW MORE?
If you are interested in further training or information, please
visit:
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Practical Arc Flash Protection for Electrical Safety Professionals

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