TRANSMISSION LINES DESIGN and ELECTRICAL ENGINEERING HUB

The logic of protective relaying looks at a complex distribution system as an integration of various subsystems. In all cases, some common design criteria are applicable. This consists of five basic elements: (1) selectivity, (2)speed of operation (3) reliability, (4) simplicity, and (5) economics. Sometimes a sixth criterion of maintainability is also added. Selectivity. A protection system should operate so as to isolate the faulted section only. In a radial system of distribution, using inverse time relays as the primary protection, the desired selectivity is obtained by coordinating upstream relays with the downstream relays in steps, so that an upstream relay is slower than the downstream relay. This may increase the fault clearance time toward the source depending upon relay characteristics and the fault current distribution. A separate zone of protection can be established around each system element so that a fault occurring in that zone...

The Public Utility Holding Company Act of 1935 (PUHCA) erected a barrier for the entry of nonutility generators (NUGs) into the electricity generation market. The market monopoly was breached by the Public Utility Regulatory Policies Act of 1978 (PURPA). It opened the door for cogeneration and for small power production technology based on hydro, wind, and biomass, allowing them to enter the electricity market without being burdened with PUHCA requirements. Electric utilities retained some avenue through rules that allowed up to 50% ownership share in a qualifying facility (QF). Since PURPA, many utilities have established subsidiaries to exploit the potential benefits of participation in QF projects as sources of lower-risk capacity compared to plants directly built by the utility. As a result of PURPA, more than 20,000 MW of QF capacity were brought into operation. The initial purchases, which were based on the avoided cost of the utility...

Automatic transfer switch: A transfer switch that can transfer the electrical load from one power source to another without manual intercession. Bypass switch: A transfer switch for an uninterruptible power supply (UPS) that is operated automatically to transfer DC battery power to the DC-to-AC converter to sustain the AC load. The switch can be operated manually for maintenance or repair of the conversion circuitry of the UPS. Emergency power system: A separate source of electric power that can pick up all or part of an electrical load automatically following an outage of normal power. It can take over loads so rapidly that critical lights and equipment will continue to function, assuring the safety of personnel and preventing property damage or loss. Manual transfer switch: A switch that must be operated manually to transfer the electrical load from one power source to another. Normal AC power (also called commercial power): P...

Power interruptions are normal occurrence whenever there are massive weather disruption. Super storm Sandy however left around 2.8 million homes without electric power as it affected the transmission and distribution grid due to wind, gust and heavy flooding. Power interruption cost a substantial amount of money due to stoppage of salary or work payment, Cost of loss of profit opportunity, Overtime payment, Cost of loss of raw material, Cost of re-starting the process, and Cost of damaged equipment.But this super storm. But in cases like this, money is not the primary concern. The safety and health of the people within the area is. In a report by CBS news, Superstorm Sandy slammed into the New Jersey coastline with 80 mph winds Monday night and hurled an unprecedented 13-foot surge of seawater at New York City, flooding its tunnels, subway stations and the electrical system that powers Wall Street. The power was out for hundreds of thousa...

The following are recommended as minimum controls to be used in preparing sag and tension charts for OPGW as recommended by IIEE STD 1138-1994: a) OPGW sags should be such that the tensions do not exceed the limits for open supply conductors, which are given in the latest edition of the National Electrical Safety Code (NESC) or appropriate national code(s) for the country where installed. These limitations are based on the use of recognized methods for reducing the likelihood of fatigue failures by minimizing chafing and stress concentrations. b) Sag and tension recommendations regarding vibration protection should be obtained from the OPGW manufacturer or from other sources knowledgeable in the field of vibration protection of overhead cables. c) In addition, it is known that some types of cable construction exhibit increased attenuation of the optical signal at tensions, which are permitted by the National Electrical Safety Code (NESC) or appropriate ...

Swimming, wading, and decorative pools and fountains present special problems for lighting designers. Outdoor lighting must be capable of functioning properly under all weather conditions and wide temperature excursions, but electrification near bodies of water requires additional safeguards. It is imperative that all luminaires and wiring suitable for use near these installations be made to withstand long-term exposure to a wet environment. They must also incorporate features that eliminate the possibility of electrical shock to persons in or near them. An electric shock can be received near these installations in several ways, because electrical potentials exist with respect to ground and within the water itself. Any person in the pool who touches a faulty energized metal enclosure is subject to possibly fatal electrical shock because his or her body will conduct current through the water and pool to earth. For this reason NEC 20...

The single-line diagram may be used in a number of important ways in operating and maintaining an industrial or commercial power distribution system. Frequently, the single-line diagram, with all of the listed information, becomes too crowded for information to be used effectively in some of the operating activities. In those instances, it is wise to produce a set of single-line diagrams, with each different diagram in the set containing the pertinent information that is required for a particular activity or set of activities. Some of the needs for special single-line diagrams are a) Switching functions. When the primary use of the diagram is to provide information to system operators for switching in order to isolate portions for maintenance or for load control, then only the data required to make the decisions necessary for system switching are included on the diagram. Sometimes, when the distribution system is complex, a separate version of the single-line diagram in b...

Single-conversion UPS systems are those in which, during normal operation, the incoming line is used to provide power to the critical load either through a transformer or in conjunction with some series impedance. Some forms of single-conversion UPS products are classified as “line interactive”. The single conversion UPS usually provides a higher operating efficiency at lower cost than the double conversion UPS at a comparable system reliability. (Note that the recently revised NEMA PE 1-1993 [B23], identifies the single-conversion system as a “single-conversion converter.”) Unlike the double-conversion system, the incoming line to the single-conversion UPS is not rectified to produce dc power to provide input to the inverter. The normal ac power is supplied directly to the critical load through a series inductor or a linear or ferroresonant transformer. The normal ac also supplies a small charger used to maintain the UPS batteries in a fully charged condition. Thus the b...

To fabricate high-field magnets, flexible tapes, having the advantage of a small distance from the brittle A15 compound to the neutral phase in bending direction, have been used successfully. The large area-to-thickness ratio of the A15 layer leads to instability (flux jumps), especially if magnets have a rapid ramping rate. The solid-state diffusion process, as used for bronze conductors of Nb3Sn and V3Ga (31), has solved this problem, by dividing the core material into plenty of fine filaments. The formation of A15 layers is principally limited by the amount of Sn and Ga in the bronze. The solubility of Sn in Cu is 8.5 at.% and for Ga in Cu is 20 at.%. Bronze with about 7.5 at.% Sn or about 18 at.% Ga has been used. The diffusion process forms the A15 layer until the equilibrium for a given temperature is established. At a temperature of 620#C to 700#C, the diffusion for Ga ends at a remaining concentration at 14 at.% to 15 at.% Ga in the matrix. Sn diffusion from...

Residential electric water heaters are listed under UL Standard 174, Household Electric Storage Tank Water Heaters. Electrical contractors many times are also in the plumbing, heating, and appliance business. They need to know more than how to do the electrical hookup. The following text discusses electrical as well as other data about electric water heaters that will prove useful. All homes require a supply of hot water. To meet this need, one or more automatic water heaters are generally installed as close as practical to the areas having the greatest need for hot water. Water piping carries the heated water from the water heater to the various plumbing fixtures and to appliances such as dishwashers and clothes washers. The wattage ratings of electric water heaters can vary greatly, depending on the size of the heater in gallons, the speed of recovery desired, local electric utility regulations, and codes. Typical wattage ratings are 1500, 2000, 2500, 3000, 38...

The central fiber optic unit shall be designed to house and protect the optical fibers from damage due to forces such as crushing, bending, twisting, tensile stress, and moisture. The fiber optic unit and the outer stranded metallic conductors shall serve together as an integral unit to protect the optical fibers from degradation due to vibration and galloping, wind and ice loadings, wide temperature variations, lightning and fault current, as well as environmental effects that may produce hydrogen. The fiber optic unit may include an aluminum tube and/or channeled aluminum rod, but is not limited to these designs. Aluminum tube The fiber optic unit may include an aluminum tube to house the fibers. The aluminum tube may be fabricated as a seamless extruded tube, seam welded, or a tube without a welded seam. Aluminum rod An aluminum rod may be fabricated with one or more channels or grooves and formed into a helix to house the optical fibers. An oute...

High-voltage underground cables have been installed in response to adverse public response to the visually offensive high-rise transmission towers in or close to populated communities. Underground cables rated for voltages as high as 500 kV have been developed. They were first placed in service in the United States in 1976. Traditionally, underground cable systems have been installed in cities and other heavily populated areas, where open high-voltage lines present a safety hazard. They have also been installed where overhead lines were not practical, in locations such as air port approaches because of aircraft safety issues, or water crossings where overhead lines are not feasible because of interference with water traffic. For crossing large bodies of water, trenches are dug or dredged to depths related directly to the voltage being carried by the cable, and the crossings are marked near the shore lines. Extruded dielectric cables have become the U.S. standard for...