In electrical power systems, the fault frequently involves arcing and burning of wiring exposed to mechanical damage and other insulation stresses including wiring not fixed and connected by flexible ...cords and cables. IEC Standard 60364 ends the design of electric power systems at the outlets of branch circuits or at the fixed equipment. A complete design should include the connections of portable equipment and of extension cords (as requested by NFPA 70) that are exposed to arc faults and may cause fire and/or electric shock hazards. Since cords supplying Class II equipment are without a grounding protection conductor, the failure of the double insulation, caused by external damage, is unlikely to be easily detected as a ground fault. Protection must be provided to prevent the fault from extinguishing itself without being detected and remaining energized, thus presenting an electric shock hazard by direct contact with a live part, rendered accessible after local insulation failure. The authors highlight this worst case and suggest the protection achieved by wiring the circuits, particularly extension cords, with special power cables. Ground-fault forced cables (GFFCs) convert a line-to-line fault into a line-to-ground fault, that will be detected and protected by ordinary ground-fault protective devices. By adopting the GFFC type of cables internally to Class II equipment, the disconnecting protection could also be extended to equipment.
Daylight in interior offers a considerable contribution of energy saving, the key is to design an integrated lighting system between the electric lighting system configuration and its control ...strategy. An optimal lighting system has to consider the different presence of daylight in the zones to arrange the most favorable luminaires layout. An automatic control system could be employed to switch or dim selected groups of luminaires. The paper suggests a criterion to evaluate the yearly daylight impact on energy performance of internal lighting according to daylight availability, the lighting system layout, and the control system arranged. A simplified evaluation by the daylight lumen method is useful for designers to estimate the operation costs in reference to the initial costs in preliminary design.
This paper provides a summary of the IEC protection against electric shock. This protection is provided by appropriate basic measures as follows: (1) for protection both in normal service and in case ...of a fault (against both direct and indirect contact), use low and safe voltage of 50 V and below; (2) for protection in normal service (against direct contact), use insulation and/or enclose live parts or use isolation distance; and (3) for protection in case of a fault (against indirect contact), prevent conducting parts not normally energized from becoming live. This is accomplished by grounding and automatic disconnection of the supply, by use of Class II equipment (as double or equivalent insulation), or by separating the supply from ground, IEC publication 364-4-41 "Electrical installations of buildings", (Part 4, Chapter 41) classifies types of system grounding as TN-system, TT-system, and IT-system. Development of this summary is based on actual hazard risk analysis of potential incidents to suggest criterion by which the appropriate measures can be applied to avoid or mitigate injury or damage.
Natural daylight in interiors has two main characteristics: It is extremely pleasant to humans, and it is a free energy. The electric lighting system has to be able to combine the daylight ...contribution with consequent savings on the energy bill. The application of sensors, control systems, and information technologies can reduce significantly the need for human work. Controlling the electric lighting in such a way that the daylighting penetration matches the lighting level to the actual need allows saving on the energy costs and improving the human comfort and efficiency. This paper highlights that lighting controls work with effectiveness if the lighting system is well structured both in luminaire arrangement and control group subdivision, according with a comprehensive approach that considers working zones and daylight contributions. At this aim, this paper suggests an adaptive criterion and a rule of thumb to evaluate the daylight availability and its internal penetration since the preliminary design.
The growing demand for energy by end users linked to the diffusion of electric vehicles poses new challenges that must be addressed in order to guarantee an efficient and safe power supply network. A ...large diffusion of electric vehicles poses the need to have fast electric charging stations and parking lots for slow charging and topping up of the charge. The spread of electric vehicles is linked to a growing environmental sensitivity of people, who see electric mobility as a possible solution to greenhouse gas pollution. A large diffusion of electric vehicles poses the need to have fast electric charging stations and parking lots for slow charging and topping up of the charge. This paper proposes a solution to electrify a large vehicle park, consisting of numerous parking spaces, in order to rationalize its design. The EV parks will have an important impact on the energy demand of the building connected to it, but also on the development of microgrids.
The USA and Europe use different standards to provide electrical safety for employee workplaces. This paper examines the two standards NFPA70E and EN 50110, shows some of the similarities and ...differences, and looks at the possibilities for a gradual harmonization between the two systems. The paper would contribute to improve the electrical safety continuity in the worldwide globalization efforts.
In the operation of electrical installations, risk assessment evaluates hazards and conflicts. A kinematics analogy for analyzing the risk of "collisions" offers a new approach for operational ...procedures and allows the introduction of a "transition" theory for intersections. The architecture of electrical installations can be designed in increasing complexity related to its exigencies, taking actions on multiple sources and on the configuration. Analogies between the operation of highway intersections of multiple traffic lanes and the operation of nodes of electrical power systems are proposed as offering an equivalent well-known way for examining constraints in the transitions, for facilitating the understanding of the mathematical description, and for suggesting new approaches and new methodologies for solutions. Automatic transfer switches also assisted by engine generators and UPSs are available as basic equipment to support transitions. This paper describes the special configuration of the node "double two," constituted by two automatic transfer switches connectible in parallel.
Maintenance personnel must take the clearing procedures, operating the necessary steps to assure that the system or portion of the system on which they plan to work is in an electrically safe working ...condition. Complexity of the electrical system normally determines the level of detail required for planning the system clearing procedures. The clearing procedures should be completely written, checked, and understood by all persons involved before applying them to any portion of the power distribution system. This paper reviews and enhances previous papers. It investigates the basic concepts and definitions to give prominence to operating bonds and to help the procedure/project with alternative, independent ways. It proposes some simple rules and bond definitions to facilitate programming. It introduces a graphical representation and a logic code to write symbolically the electrical status. Both intuitive and mathematical approaches can heighten understanding. The model allows memorizing visually the logic procedures, counting the necessary locks, and executing an autocheck of the clearing procedure.
