Causes of Electrical Fires

Causes of Electrical Fires Points : causes of electrical fires, fires in electrical power stations/substations/plants are caused by one or more of the following As per philosophy of safety management, the root cause behind occurrence of an accident is either.
(1) Lapse in Safety Management. Several acts of negligence, carelessness usually accumulate and increase the fire hazard, e.g., lack of house keeping, poor quality of wiring, old and worn out equipment not replaced, loose connections not repaired, gas leaks ignored, poor quality of testing and maintenance.
(2) Human Error/Negligence Lack of awareness, Lack of training.
(3) Accident beyond human control.
Behind every fire incidence there may be several “chance misses” which did not materialize.
Fire accidents can be prevented and eliminated by adopting scientific engineering approach. Fires in Electrical power stations/substations/plants are caused by one or more of the following: 1. Electric Arcs, Flash Over, Short Circuits Failure of air insulation causes flashovers and arcs which continue and result in fires of surrounding flammable material in the plant/equipment/building. The fire risk increases with higher voltage levels and higher short circuit levels in the plant and use of flammable/explosive materials in the plant. 2. Loose connections resulting in sparks. Loose connection at terminals of equipment, joints in conducting path, butt joints fastened by nut bolts, joints between two cables etc. in main circuit/auxiliary circuit, temporary supply connections etc. are source of sparks, over heating, melting and fire. 3. Corona discharge/Arcing grounds at sharp, low clearance points The phase to ground capacitance gels charged from supply voltage. At some sharp points of low clearance distance, arcing takes place due to corona discharge during moist weather. The capacitance gets discharged forming arcing ground. The capacitance is charged again by supply voltage and discharges again through arcing ground. This process continues. If an inflammable material (wood/board/paper/cloth/oil drum etc. is in the vicinity, the same may catch fire due to the arcing ground. 4. Arcs due to Static Charges Statically induced charges, if not discharged, get accumulated on rubbing insulating surfaces/system capacitance. When earthed component is brought near the charged surface, spark discharge takes place. A flammable material in the vicinity may catch fire. 5. Welding sparks, hot metals Sparks and hot molten beads fall down during welding of structural steel work at heights. These sparks and hot metals fall in packing cases, stored flammable material on ground and fire is initiated. Care should be taken to remove flammable material from construction site. 6. Welding of Oil Filled Tanks Transformer tanks, oil storage tanks are carelessly welded at site to step leaks, the result is explosion of the oil filled tanks due to fire caused by welding. 7. Hot Resistors In many cases, the resistor elements in the equipment are under rated for current. The actual current f1o is more than the rated current of the resistors used. The resistors become red hot and release heat. If a flammable material is in the vicinity fire is initiated. 8. Bursting of Capacitor Cans Over voltage causes over heating of capacitor wilts, the capacitor units may burst releasing smoke and flame. Capacitor units must be properly encased for safety. 9. Exothermic Reaction Some chemical reactions release heat and create spontaneous fires. For examples coal stored in large quantity in open weather in sunlight (at high temperature) oxidizes with a possibility of spontaneous combustion and fire. Special storage procedures arc recommended to prevent fires. 10. Fires and Explosions in Oil Filled Equipment Electrical fires and explosions are more likely with transformers and other oil filled equipment like CTs. Bushings, Oil Circuit Breakers. Hot spot temperature of transformer winding and oil should not exceed following limits. 11. Switching Surges Following circuit breaker duties generate over voltages which may cause external flashovers/internal flashovers in the equipment: (1) Capacitor switching with restrict in circuit breaker (2) Inductive current switching with current chopping in circuit breaker. Internal flashover results in subsequent arcing and bursting of porcelain insulators. External flashover result in faults and outage. Surroundings of capacitor and breakers installations must be kept very clean and free from flammable materials and fenced. 12. Internal arcing in Metal Clad Switchgear. With minimum oil circuit breakers, breaker failure results in explosion inside metal clad switchgear. With vacuum and SF6. circuit breakers, the explosion risk is eliminated. Over voltages may cause internal flashovers. The insulating partitions and cable joints must be of fire retarding materials. 13. Fuels for Power generation, Furnace Burners Fuels include, diesel oil, furnace oil, Naptha, Coal etc. these are to be stored, handled, carefully. Leakages and subjecting to hot sport must be avoided. 14. Bulk Gas Systems These include Hydrogen for generator cooling. Ammonia for flue gas neutralizing, propane for burner initiation. These gases are highly inflammable. They must be handled, stored, used with safety procedures. Fires and explosions occur due to leakage and intense hot spots. 15. Discharge of Static Charges Tanks and Metal parts placed below transmission line and insulated form ground by rubber tires may have static charge. Static charges may develop in conveyor belts. The same must be discharged by connecting to earth. Otherwise, the discharge may initiate a spark.