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Electrical substation safety is an important issue in utility networks as well as large industrial installations and requires adequate attention in the stages of system planning, design, installation, operation and maintenance. A number of serious accidents including fatalities occur every year in industrial establishments due to accidents involving electricity, resulting in huge financial losses and wasted man-hours. Electrical safety is a well-legislated subject and the various Acts and Regulations lay a lot of stress on the responsibility of both employers and employees in ensuring safe working conditions. In this workshop, we will take a look at the theoretical aspects of safety as well as the practical and statutory issues. Safety is not simply a matter of taking precautions in the workplace. It has to start at the stage of equipment design. Safety should be built into the design of electrical equipment and it is the responsibility of every manufacturer of electrical equipment to remove every possible hazard that can arise from its normal use. Correct selection and application of electrical machinery is also important for ensuring safety. A thorough inspection during initial erection and commissioning as well as on a periodic basis thereafter is also very essential to ensure safety. Batteries used in substations need particular attention since they contain toxic materials such as lead, corrosive chemicals such as acid or alkali. Electrical safety is not just a technical issue. Accidents can only be prevented if appropriate safety procedures are evolved and enforced. This includes appropriate knowledge of equipment and systems imparted through systematic training to each and every person who operates or maintains the equipment. We will cover all these aspects in detail. MORE INFORMATION: http://www.idc-online.com/content/practical-electrical-substation-safety-engineers-and-technicians-28
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Practical Electrical Substation Safety for Engineers & Technicians
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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 electrical equipment
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Electrical Hazards
• Electric shock and associated effects• Injuries by electric shock combined with fall• Burns on skin at point of contact• Internal organ damage due to passage of electricity through body• Flash-over causing external burns
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Mechanical hazards
• Injuries from moving parts of static machinery• Injuries from moving vehicles• Injuries from falling objects (including head injuries)• Injuries from flying objects following an explosion• Injuries to eye from moving particles• Injuries to eye from prolonged exposure to bright light• Loss of hearing due to prolonged exposure to noise
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Hazards from toxic materials
• External contact on skin and eyes
• Ingestion
• Inhalation
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Dealing with fire hazard
• Fire is often initiated by other hazards (electrical, explosion due to hazardous gases present in the environment etc.)
• Once initiated, it can be self sustaining
• Dealing with fire:– Prevention is often the best way– Alarm of incipient fire before it spreads– Fire fighting measures as appropriate
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Hot surfaces/liquids/gases• Many electrical equipment have fairly high surface temperatures• Many industries also handle materials at high temperatures• Effects:
– Burns due to contact– Explosions (e.g. molten steel and water)
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Handling of cold liquids
• Burns due to contact
• Explosions (e.g. liquid oxygen)
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Handling of corrosive liquids• Acids and alkalis are corrosive
• Safety issues– Burns/irritation due to contact with skin– Loss of sight or serious injury of eyes– Danger of ingestion– Danger of inhalation (fumes)
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Handling of explosive gases• Explosion by formation of explosive mixtures of
combustible gases and oxygen in air• Source of ignition is often electrical• Effects
– Burns by fire accompanying explosion– Injuries from flying objects following an explosion– Damage to limbs/internal injuries
• Prevent– Formation of explosive mixtures– Ignition– Damage due to explosion
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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
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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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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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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
• 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 problems• Proper periodic inspection and prompt repairs
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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
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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
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