IEEE C37 10-2011 pdf free download – IEEE Guide for Investigation, Analysis, and Reporting of Power Circuit Breaker Failures.
4. Procedure for investigation of circuit breaker failures For major failures, the local personnel should be adequately trained to deal with immediate hazards, isolation, grounding, etc.
These personnel will likely not be in charge of the investigation of the failure. Therefore, although 4.2 through 4.6 describe what needs to be done, an organization should decide who will be trained to perform the actions at the scene required to preserve evidence, such as those listed in item a), b), d), and e) in 4.2, as well as contacting the appropriate internal group who will organize or lead the formal investigation. There may be a separate protocol for different levels of investigation, depending on the nature and initially perceived severity of the failure. The user and manufacturer are very much encouraged to agree on the approach to evaluating the failure. Identify the prime reason for the investigation—e.g., is the prime importance to find the root cause of the failure or is it to repair the circuit breaker and return it to service? The method of investigation and disassembly could be quite different under these two scenarios.
4.1 Determining the hazards and risks associated with the circuit breaker inspection Electrical hazards must be considered during the circuit breaker failure investigation. Some components adjacent to the circuit breaker under investigation, as well as the parts of the control and protection circuits could remain energized or become energized during the investigation. Appropriate isolation and temporary protective grounding must be established prior to the investigation. Proper personal protection should be selected and used based on the company safety policies and/or results of the arc-flash studies. The failure of any electrical equipment could result in some level of hazardous material in, on, or around the circuit breaker site. These materials may be visible [such as an ash or discoloration of component(s)] or may be invisible products.
One must recognize that arc deposited residue may contain material that is hazardous to those working in and around the failed component(s). It is generally not possible to visually determine whether health hazards are present. A first level assumption must be made that the materials in and around the failure are hazardous until clarification and classification has been confirmed, generally from the manufacturer. If the equipment vendor cannot provide verification of the material content, you should arrange for the material to be sampled and identified by a specialist before anyone is exposed. Many workplace health and safety regulations apply in general (including OHSA, NFPA 70E, IEEE Std 1584, and NESC C2 in the USA).
Follow company procedures and practices. Use personal protective equipment (PPE) that is appropriate to the worksite and conditions. In addition, the following discussion describes some of the possible hazards. Some older circuit breakers incorporated arc chute designs that contained asbestos and that may also include levels of radon. The percentage content of these two materials varied from one manufacturer to the next. Some early models of power circuit breakers also incorporated mercury-filled switches in the circuit breaker cell design. Some older oil-filled circuit breakers may contain oil with polychlorinated biphenyl (PCB). Asbestos, mercury, and PCB are materials known to be hazardous to humans. A high degree of expertise is required to safely execute the environmental requirements for a safe investigation. Arc chutes were often constructed with some proportion of asbestos to resist the high temperatures of the electrical arc. Although tightly bound to the base material and not easily released to the atmosphere, (known as “non friable” asbestos) if these types of arc chutes are severely abraded, they may release dust that can become a hazard. When disturbed, flaking occurs resulting in airborne particles.
A failure of a circuit breaker containing asbestos will distribute a certain level of airborne and residual contamination. While asbestos has been banned by the environmental protection agencies for most countries, electrical equipment containing asbestos has been and continues to be in service even after more than 40 years.
A similar hazard can exist with asbestos wiring if it is shredded in the failure process. More recently, high-voltage circuit breakers utilize Sulfur Hexafluoride (SF 6 ) gas as the insulation and interruption medium. SF 6 is heavier than air and will not support life. Because SF 6 is heavier than air, SF 6 gas can accumulate or be trapped in low “pockets.” There can be a risk of asphyxiation and inhalation of toxic gases when SF 6 is released in an indoor substation. If released into the atmosphere, precautions should be observed in nearby trenches, depressions, and other locations where the gas can accumulate for short periods of time before dispersing into the atmosphere. Any tank previously containing SF 6 should not be entered without thorough ventilation and checks for suitable breathing atmosphere. Arced SF 6 gas is initially accompanied by a strong and irritating odor indicating toxic decomposition products. These products are injurious and exposure to them should be avoided. The arc byproduct powders are reactive with moisture and, if inhaled, could cause irritation in the nose, throat, and lungs. Contact with body perspiration could cause skin irritation.IEEE C37 10 pdf download