Electrical tree analysis

Fussell, J. B. 1975, Computer Aided Fault Tree Construction for Electrical System and Fault Tree Analysis, SIAM, Philadelphia, PA, p 37. 

Electrical trees are essentially breakdown channels whose size, typically 50 to 200 microns, together with the large variations in impurity concentrations in the surrounding polyethylene, makes the identification of the impurities associated with both kinds of trees very difficult by traditional techniques. The use of micro-PIXE for the location and analysis of trace elements in electrical and water trees found in the polyethylene insulation of high voltage cables will be described. 

Sarathi, R. Das, S. Kumar, C.R.A. Velmurugan, R. Analysis of failure of crosslinked polyethylene cables because of electrical treeing a physicochemical approach. J. Appl. Polym. Sci. 2004, 92, 2169-2178. 

In conventional fault tree analysis, one of the biggest benefits of the technique is that it highlights common cause events, i.e., those events that occur in two or more places on the tree and thus bypass safeguards. A common example would be electrical power failure. Loss of power could cause equipment to fail and could also lead to failure of some of the backup systems. 

The DBA fire scenario was an electrical wiring short or overheats that caused an electrical fire. Then the fire spread to combustible packaging material and spread to involve all of the radioactive material in storage. Power isolation could prevent a fire of combustible material other than the electrical wiring if the short or overheat condition were detected promptly by an operator or isolated by an automatic circuit protection device (circuit breaker). To investigate fire termination by power isolation, the event tree analysis for this DBA considered three scenario variations ... 

The radioactive material storage area is in continuous operation to store radioactive material, thus, at least some of the electrical circuits are in use for all of the 8760 hours per year. Failure probabilities for the various initiating events, operator response, system operation, and barrier resistance in the event tree analysis are as follows ... 

Sequences 6 and D correspond to hazard event RS-1 of the hazard analysis from Appendix 3C. The assessed event frequency per year for hazard event RS-1 was frequency bin III. This agrees well with the Sequence B frequency bin of III in the event tree analysis but not with the Sequence D frequency bin of IV. Sequence D was not considered typical of the overall operation of a radioactive material storage area. The failure to detect an electrical short or overheat and remove power in Sequence D depended on an operator being present Since operators are only present in a radiological material storage area approximately 5% of the time, this operating condition was not assessed as typical. Thus, the event tree analysis confirms the frequency assessment of the hazard analysis. 

The recommended techniques for preliminary hazard analysis are energy trace and barrier analysis (ETBA) and failure modes and effects analysis (FMEA). Recommended techniques for system and subsystem hazard analyses are FMEA, fault tree analysis (FTA), common cause analysis, sneak circuit analysis (for electrical, electronic, and some hydraulic or pneumatic circuits) and, of course, software hazard analysis for software. 

The hardware safety of medical devices is important because many of their parts, such as electronic parts, are vulnerable to factors such as electrical interferences and environmental stresses. This calls for analysis of each part of a medical device with respect to safety and potential failmes. There are several methods that can be used to perform such analysis, two of which are failure modes and effect analysis (FMEA) and fault tree analysis (FTA). 

Fault Tree Analysis Module of ITEM Tool Kit (Item Software [USA] Inc.) SAPHIRE (formerly IRRAS, U.S. Nuclear Regulatory Conunission) Probabilistic Risk Assessment Workstation (Electric Power Research... 

EPRI (2005). Fault Tree Analysis System. CAFTA 5.2 software. Data Systems Solutions/Electric Power Research Institute, Palo Alto, CA, USA. 

For this reason, more and more standards and guidelines for the development of safety-relevant systems demand safety analyses for the system and the software as part of a rigorous development process. Examples of this are lEC 61508 [1], lEC/TR 80002 [2], MISRA safety analysis guidelines [3], and ISO 26262 [4]. ISO 26262 is a committee draft for the development of road vehicles. It defines requirements on the development of electrical and electronic systems and particularly requirements on the development of software, which include qualitative safety analysis for software architecture as well as for software unit design. However performing a qualitative safety analysis technique such as failure mode and effect analysis (FMEA) or fault tree analysis (FTA) on software architectmal design is a complex task. One reason for this is that safety analyses do not fit well with software architectural design and do not... 

Reliability block diagrams are, similar as the fault tree analysis, are considered in ISO 26262 as example for deductive analysis. The blocks can be logically put into relations through Boolean algebra. If the blocks are quantified, the relations can also be described mathematically, whereas such descriptions are used as a foundation for formal description models. The simplest quantitative method is a simple summing up of the failure rates of the individual components of a function. The method is also called Part Count Method , which simply based on an addition of failure rates of electric parts. 

Function event trees include primarily the engineered safety features of the plant, but other systems provide necessary support functions. For example, electric power system failure amid reduce the effectiveness of the RCS heat-removal function after a transient or small UJ( A. Therefore, EP should be included among the systems that perform this safety function. Siipfiort systems such as component-cooling water and electric power do not perform safety functions directly. However, they significantly contribute to the unavailability of a system or group of systems that perform safety functions. It is necessary, therefore, to identify support systems for each frontline ssstcm and include them in the system analysis. 

The use of component logic models to build system fault logic has been discussed by several authors for chemical and electrical systems (Powers and Thompkins, 1974 Fussell, 197.S and Powers and Lapp, 1976). In addition, generic sabotage fault trees have been used for some time in the analysis of security concerns for nuclear power plants (NUREG /CR-0809, NUREG/CR. 121,... 

Results of the analysis are proposed in Table 8. Cultivation gives an important contribution to the final impact of truffle sauce, while truffle production has a reduced impact, because it is a very extensive production. Olive trees cultivation uses fertilizers, diesel fuel for field operations, electricity for the olives harvest, herbicides and pesticides. 

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