Three-phase electric power

Three-phase electric power is a common method of alternating current electric power generation and distribution. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power, it is used to power large motors and other heavy loads. A three-wire three-phase circuit is more economical than an equivalent two-wire single-phase circuit at the same line to ground voltage because it uses less conductor material to transmit a given amount of electrical power. Polyphase power systems were independently invented by Galileo Ferraris, Mikhail Dolivo-Dobrovolsky, Jonas Wenström, John Hopkinson and Nikola Tesla in the late 1880s; the conductors between a voltage source and a load are called lines, the voltage between any two lines is called line voltage. The voltage measured between any line and neutral is called phase voltage. For example, for a 208/120 volt service, the line voltage is 208 Volts, the phase voltage is 120 Volts. In a symmetric three-phase power supply system, three conductors each carry an alternating current of the same frequency and voltage amplitude relative to a common reference but with a phase difference of one third of a cycle between each.

The common reference is connected to ground and to a current-carrying conductor called the neutral. Due to the phase difference, the voltage on any conductor reaches its peak at one third of a cycle after one of the other conductors and one third of a cycle before the remaining conductor; this phase delay gives constant power transfer to a balanced linear load. It makes it possible to produce a rotating magnetic field in an electric motor and generate other phase arrangements using transformers; the amplitude of the voltage difference between two phases is 3 times the amplitude of the voltage of the individual phases. The symmetric three-phase systems described here are referred to as three-phase systems because, although it is possible to design and implement asymmetric three-phase power systems, they are not used in practice because they lack the most important advantages of symmetric systems. In a three-phase system feeding a balanced and linear load, the sum of the instantaneous currents of the three conductors is zero.

In other words, the current in each conductor is equal in magnitude to the sum of the currents in the other two, but with the opposite sign. The return path for the current in any phase conductor is the other two phase conductors; as compared to a single-phase AC power supply that uses two conductors, a three-phase supply with no neutral and the same phase-to-ground voltage and current capacity per phase can transmit three times as much power using just 1.5 times as many wires. Thus, the ratio of capacity to conductor material is doubled; the ratio of capacity to conductor material increases to 3:1 with an ungrounded three-phase and center-grounded single-phase system. Constant power transfer and cancelling phase currents would in theory be possible with any number of phases, maintaining the capacity-to-conductor material ratio, twice that of single-phase power. However, two-phase power results in a less smooth torque in a generator or motor, more than three phases complicates infrastructure unnecessarily.

Three-phase systems may have a fourth wire in low-voltage distribution. This is the neutral wire; the neutral allows three separate single-phase supplies to be provided at a constant voltage and is used for supplying groups of domestic properties which are each single-phase loads. The connections are arranged so that, as far as possible in each group, equal power is drawn from each phase. Further up the distribution system, the currents are well balanced. Transformers may be wired in a way that they have a four-wire secondary but a three-wire primary while allowing unbalanced loads and the associated secondary-side neutral currents. Three-phase supplies have properties that make them desirable in electric power distribution systems: The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load; this makes it possible to reduce the size of the neutral conductor because it carries little or no current. With a balanced load, all the phase conductors so can be the same size.

Power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations. Three-phase systems can produce a rotating magnetic field with a specified direction and constant magnitude, which simplifies the design of electric motors, as no starting circuit is required. Most household loads are single-phase. In North American residences, three-phase power might feed a multiple-unit apartment block, but the household loads are connected only as single phase. In lower-density areas, only a single phase might be used for distribution; some high-power domestic appliances such as electric stoves and clothes dryers are powered by a split phase system at 240 volts or from two phases of a three phase system at 208 volts. Wiring for the three phases is identified by color codes which vary by country. Connection of the phases in the right order is required to ensure the intended direction of rotation of three-phase motors. For example and fans may not work in reverse. Maintaining the identity of phases is required if there is any possibility two sources can be connected at the same time.

Urban planning education

Urban planning education is a practice of teaching and learning urban theory and professional practices. The interaction between public officials, professional planners and the public involves a continuous education on planning process. Community members serve on a city planning commission, council or board; as a result, education outreach is an ongoing cycle. Formal education is offered as an academic degree in urban, city or regional planning, awarded as a bachelor's degree, master's degree, or doctorate. Since planning programs are small, they tend not to be housed in distinct "planning schools" but rather, as part of an architecture school, a design school, a geography department, or a public policy school, since these are cognate fields. Speaking, planning programs in architecture schools focus on physical planning and design, while those in policy schools tend to focus on policy and administration; as urban planning is such a broad and interdisciplinary field, a typical planning degree program emphasizes breadth over depth, with core coursework that provides background for all areas of planning.

Core courses include coursework in history/theory of urban planning, urban design, land use/planning law, urban economics, planning practice. Many planning degree programs allow a student to "concentrate" in a specific area of interest within planning, such as land use, environmental planning, community development, economic development, historic preservation, international development, urban design, transportation planning, or geographic information systems; some programs permit a student to concentrate in real estate, graduate real estate education has changed giving rise to specialized real estate programs. Bachelor of Planning is an undergraduate academic degree designed to train applicants in various aspects of designing, engineering and resolving challenges related to urban human settlements, it is awarded for a course of study that lasts up to four years and contextual to modern challenges of urbanisation. It goes into the techniques and theories related to settlement design starting at the site planning level of a neighbourhood and moving up to the regional city planning context.

Understanding relations between built forms and the citizens in cities and rural areas, their implications on local environment, supporting utilities, transport networks, physical infrastructure forms the core of the planning course. With an engineering orientation, the graduates emerging as urban planners are equipped with not only tools for rational comprehensive planning but participatory and social development; the degree may be awarded as a Bachelor of Arts in Geography with an emphasis in urban planning, Bachelor of Arts in Urban Planning, or Bachelor of Science in Urban and Regional Planning. The distinction reflects university policies, or some universities may have greater course offerings in urban planning, sociology, or a related degree; the Master of Urban Planning is a two-year academic/professional master's degree that qualifies graduates to work as urban planners. Some schools offer the degree as a Master of City Planning, Master of Community Planning, Master of Regional Planning, Master of Town Planning, Master of Planning, Master of Environmental Planning or in some combination of the aforementioned, depending on the program's specific focus.

Some schools offer a Master of Master of Science in Planning. Regardless of the name, the degree remains the same. A thesis, final project or capstone project is required to graduate. Additionally, an internship component is always mandatory due to the high value placed on work experience by prospective employers in the field. Like most professional master's degree programs, the MUP is a terminal degree. However, some graduates choose to continue on to doctoral studies in urban planning or cognate fields; the Ph. D. is a research degree, as opposed to the professional MUP, thus focuses on training planners to engage in scholarly activity directed towards providing greater insight into the discipline and underlying issues related to urban development. Accreditation is a system for recognizing educational institutions and professional programs affiliated with those institutions for a level of performance and quality; the Planning Accreditation Board is the sole accreditor of planning programs in the United States.

The Planning Accreditation Board accredits graduate and undergraduate planning programs in the United States and Canada. As of January 1, 2016, PAB accredits 15 undergraduate programs and 71 graduate programs in 75 North America Universities; the Planning Accreditation Board accredits university programs in North America leading to bachelors and masters degrees in planning. The accreditation process is based on standards approved by the PAB and its sponsoring organizations: the American Planning Association. Graduation from a PAB accredited program allows a graduate to sit for the American Institute of Certified Planners Certification Exam earlier in their career than a student with a degree from a non-accredited program or school. Programs that desire accreditation through the PAB must apply for candidacy status; the program seeking candidacy must demonstrate that they meet the five preconditions to accreditation. The five preconditions are: Program graduation of at least 25 students in the degree.

Program's parent institution must be accr

Princess Elizabeth Land

Princess Elizabeth Land is the sector of Antarctica between longitude 73° east and Cape Penck. The sector is claimed by Australia as part of the Australian Antarctic Territory, although this claim is not recognized. Princess Elizabeth Land is located between 64°56'S and 90°00'S and between 73°35' E and 87°43'E, it is divided into two sectors: Ingrid Christensen Coast, 73°35'E to 81°24'E Leopold and Astrid Coast, 81°24'E to 87°43'EIt is bounded on the west by Amery Ice Shelf, Mac. Robertson Land, on the east by Kaiser Wilhelm II Land. Princess Elizabeth Land was discovered on 9 February 1931, by the British Australian and New Zealand Antarctic Research Expedition under Sir Douglas Mawson. Princess Elizabeth Land was named by Mawson after Princess Elizabeth, who became Queen Elizabeth II. Though Australia claims the entirety of this land, it is home to Russian stations including Vostok Station and Mirny Station which supplies it. List of mountains of Princess Elizabeth Land Queen Elizabeth Land Queen Elizabeth Islands Australian Antarctic Gazetteer: Maps of the Australian Antarctic Territory ANTARCTICA.

TXT — listing of most Antarctica features in one USGS file