electrical engineering construction

The term geothermal comes from the Greek geo, meaning earth, and therine, meaning heat, thus geothermal energy is energy derived from the natural heat of the earth. The earth’s temperature varies widely, and geothermal energy is usable for a wide range of temperatures from room temperature to well over 300°F. For commercial use, a geothermal reservoir capable of providing hydrothermal (hot water and steam) resources is necessary. Geothermal reservoirs are generally classified as being either low temperature (<150°c)>150°C). Generally speaking, the high temperature reservoirs are the ones suitable for, and sought out for, commercial production of electricity. Geothermal reservoirs are found in “geothermal systems,” which are regionally localized geologic settings where the earth’s naturally occurring heat flow is near enough to the earth’s surface to bring steam or hot water, to the surface. Examples of geothermal systems include the Geysers Region in Northern California, the Imperial Valley in Southern California, and the Yellowstone Region in Idaho, Montana, and Wyoming.

Dry Steam Power Plant
Power plants using dry steam systems were the first type of geothermal power generation plants built. They use steam from the geothermal reservoir as it comes from wells and route it directly through turbine/generator units to produce electricity. An example of a dry steam generation operation is at the Geysers Region in northern California.










Flash Steam Power Plant
Flash steam plants are the most common type of geothermal power generation plants in operation today. They use water at temperatures greater than 360°F (182°C) that is pumped under high pressure to the generation equipment at the surface. Upon reaching the generation equipment, the pressure is suddenly reduced, allowing some of the hot water to convert or “flash” into steam. This steam is then used to power the turbine/generator units to produce electricity. The remaining hot water not flashed into steam, and the water condensed from the steam, is generally pumped back into the reservoir. An example of an area using the flash steam operation is the CalEnergy Navy I flash geothermal power plant at the Coso geothermal field.





Binary Cycle Power Plant
Binary cycle geothermal power generation plants differ from dry steam and flash steam systems because the water or steam from the geothermal reservoir never comes in contact with the turbine/generator units. In the binary system, the water from the geothermal reservoir is used to heat another “working fluid,” which is vaporized and used to turn the turbine/generator units. The geothermal water and the “working fluid” are each confined in separate circulating systems or “closed loops” and never come in contact with each other. The advantage of the binary cycle plant is that they can operate with lower temperature waters (225°F to 360°F) by using working fluids that have an even lower boiling point than water. They also produce no air emissions. An example of an area using a binary cycle power generation system is the Mammoth Pacific binary geothermal power plants at the Casa Diablo geothermal field.

Coal-fired units produce electricity by burning coal in a boiler to heat water to produce steam. The steam, at tremendous pressure, flows into a turbine, which spins a generator to produce electricity. The steam is cooled, condensed back into water, and returned to the boiler to start the process over.

For example, the coal-fired boilers at TVA’s Kingston Fossil Plant near Knoxville, Tennessee, heat water to about 1,000 degrees Fahrenheit (540 degrees Celsius) to create steam. The steam is piped to the turbines at pressures of more than 1,800 pounds per square inch (130 kilograms per square centimeter). The turbines are connected to the generators and spin them at 3600 revolutions per minute to make alternating current electricity at 20,000 volts. River water is pumped through tubes in a condenser to cool and condense the steam coming out of the turbines.

The Kingston plant generates about 10 billion kilowatt-hours a year, or enough electricity to supply 700,000 homes. To meet this demand, Kingston burns about 14,000 tons of coal a day, an amount that would fill 140 railroad cars.

Transmission lines are classified as short, medium and long. When the length of the line is less than about 80Km the effect of shunt capacitance and conductance is neglected and the line is designated as a short transmission line. For these lines the operating voltage is less than 20KV.

For medium transmission lines the length of the line is in between 80km - 240km and the operating line voltage wil be in between 21KV-100KV.In this case the shunt capacitance can be assumed to be lumped at the middle of the line or half of the shunt capacitance may be considered to be lumped each end of the line.The two representations of medium length lines are termed as nominal-T and nominal- π respectively.

Lines more than 240Km long and line voltage above 100KV require calculations in terms of distributed parameters.Such lines are known as long transmission lines.This classification on the basis of length is more or less arbitrary and the real criterion is the degree of accuracy required.

Performance of Transmission Lines
The performance of a power system is mainly dependent on the performance of the transmission lines in the system.It is necessary to calculate the voltage,current and power at any point on a transmission line provided the values at one point are known.

The transmission line performance is governed by its four parameters - series resistance and inductance,shunt capacitance and conductance.All these parameters are distributed over the length of the line.The insulation of a line is seldom perfect and leakage currents flow over the surface of insulators especially during bad weather.This leakage is simulated by shunt conductance.The shunt conductance is in parallel with the system capacitance.Generally the leakage currents are small and the shunt conductance is ignored in calculations.
Performance of transmission lines is meant the determination of efficiency and regulation of lines.The efficiency of transmission lines is defined asThe end of the line where load is connected is called the receiving end and where source of supply is connected is called the sending end.

The Regulation of a line is defined as the change in the receiving end voltage, expressed in percent of full load voltage, from no load to full load, keeping the sending end voltage and frequency constant.