TRANSMISSION & DISTRIBUTION - Electrical Engineering Objective Type Questions and Answers mcqs interview lab viva importanat questions pdf free download. Electric Power Generation, Transmission, and Distribution and Electrical Protective Equipment Final Rule The Occupational Safety and Health Administration (OSHA) updated its Electric Power Generation, Transmission, and Distribution and its Electrical Protective Equipment standards, further improving safety protections for America’s workers. Power Transmission and Distribution. Our modern day world increasingly relies on electricity to power us and make our lives possible. It is Electrical Engineers who build the generators and systems that provide electricity to cities and towns all over the world.
Electricity generation and transmission concept
The purpose of the electric transmission system is the interconnection of the electric energy producing power plants or generating stations with the loads. A three-phase AC system is used for most transmission lines.
The operating frequency is 60 Hz in the U.S. and 50 Hz in Europe, Australia, and part of Asia.
The three-phase system has three phase conductors. The system voltage is defined as the RMS voltage between the conductors, also called line-to-line voltage. The voltage between the phase conductor and ground, called line-to-ground voltage, is equal to the line-to-line voltage divided by the square root of three.
The generating station produces the electric energy. The generator voltage is usually around 15 to 25 kV. This relatively low voltage is not appropriate for the transmission of energy over long distances. At the generating station a transformer is used to increase the voltage and reduce the current.
In Figure 1 the voltage is increased to 500 kV and an extra-high voltage (EHV) line transmits the generator-produced energy to a distant substation.
The voltage is reduced at the 500 kV/220 kV EHV substation to the high voltage level and high voltage lines transmit the energy to high voltage substations located within cities.
At the high voltage substation the voltage is reduced to 69 kV. Sub-transmission lines connect the high voltage substation to many local distribution stations located within cities. Sub-transmission lines are frequently located along major streets.
Electricity distribution concept
The voltage is reduced to 12 kV at the distribution substation. Several distribution lines emanate from each distribution substation as overhead or underground lines. Distribution lines distribute the energy along streets and alleys.
Each line supplies several step-down transformers distributed along the line.
The distribution transformer reduces the voltage to 230/115 V, which supplies houses, shopping centers, and other local loads. The large industrial plants and factories are supplied directly by a subtransmission line or a dedicated distribution line as shown in Figure 1 above.
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Transmission and distribution concept
The purpose of the electric transmission system is the interconnection of the electric energy producing power plants or generating stations with the loads. A three-phase AC system is used for most transmission lines.
The operating frequency is 60 Hz in the U.S. and 50 Hz in Europe, Australia, and part of Asia. The three-phase system has three phase conductors. The system voltage is defined as the rms voltage between the conductors, also called line-to-line voltage.
Power Transmission And Distribution Book Pdf
The voltage between the phase conductor and ground, called line-to-ground voltage, is equal to the line-to-line voltage divided by the square root of three.
The figure shows the Phoenix area 230-kV system, which interconnects the local power plants and the substations supplying different areas of the city. The circles are the substations and the squares are the generating stations.
The system contains loops that assure that each load substation is supplied by at least two lines. This assures that the outage of a single line does not cause loss of power to any customer.
For example, the Aqua Fria generating station (marked: Power plant) has three outgoing lines. Three high-voltage cables supply the Country Club Substation (marked: Substation with cables). The Pinnacle Peak Substation (marked: Substation with transmission lines) is a terminal for six transmission lines. This example shows that the substations are the node points of the electric system. The system is interconnected with the neighboring systems.
As an example, one line goes to Glen Canyon and the other to Cholla from the Pinnacle Peak substation.
Electrical Power Transmission And Distribution System Pdf
In the middle of the system, which is in a congested urban area, high-voltage cables are used. In open areas, overhead transmission lines are used. The cost per mile of overhead transmission lines is 6 to 10% less than underground cables.
The major components of the electric system, the transmission lines, and cables are described briefly below.
Generation Stations
The generating station converts the stored energy of gas, oil, coal, nuclear fuel, or water position to electric energy. The most frequently used power plants are:
Thermal Power Plant
The fuel is pulverized coal or natural gas. Older plants may use oil. The fuel is mixed with air and burned in a boiler that generates steam. The high-pressure and high-temper- ature steam drives the turbine, which turns the generator that converts the mechanical energy to electric energy.
Power Transmission And Distribution Book Pdf Free DownloadNuclear Power Plant
Enriched uranium produces atomic fission that heats water and produces steam. The steam drives the turbine and generator.
Hydro Power Plants
A dam increases the water level on a river, which produces fast water flow to drive a hydro-turbine. The hydro-turbine drives a generator that produces electric energy.
Gas Turbine
Natural gas is mixed with air and burned. This generates a high-speed gas flow that drives the turbine, which turns the generator.
Electrical Power Transmission And Distribution PdfCombined Cycle Power Plant
This plant contains a gas turbine that generates electricity. The exhaust from the gas turbine is high-temperature gas. The gas supplies a heat exchanger to preheat the combustion air to the boiler of a thermal power plant. This process increases the efficiency of the combined cycle power plant.
The steam drives a second turbine, which drives the second generator. This two-stage operation increases the efficiency of the plant.
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