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EE 303 Homework #1 1. Generation subsystem 1 What are the three primary means of generating electricity? Thermal, Hydro and nuclear 2 What is the most common means of generating electricity in your home state? In Iowa, the majority of electricity is generated by coal-burning power plants. 3 Why are combined cycle units used? Combined cycle units are more efficient, converting a greater portion of thermal energy produced by combustion into electric energy. 4 At what range of voltages do generators deliver power? 480v – 30KV 5 How are the nuclear fuel rods prepared? Uranium ore --> Enriched --> Ceramic pellets --> Fuel rods 6 How is nuclear fission controlled? Nuclear fission is controlled by raising and lowering control rods into the core. 7 A simulation was used to describe nuclear fission in the tape. Based on this simulation, explain how fission occurs in your own words. Nuclear fission is a chain reaction process. It is initiated by firing a neutron at Uranium-235, which in turn releases more neutrons. These neutrons collide with other U-235 atoms and produce more and more neutrons. This process will go on and on and a chain reaction is produced. 8 What are the two types of nuclear reactors in the U.S.? Boiling-water reactor (BWR) and pressurized-water reactor (PWR). 9 Describe the process of generating steam in a pressurized water reactor. First, water is kept at a high pressure at reactor vessel, so it is prevented from evaporation. Then the heat energy is transferred from the high pressure water system to the low pressure one, transforming water into steam which is sent to the turbine later. 10 Name three methods of generating electricity using alternative energy sources. Wind energy, solar energy and geothermal energy. Transmission subsystem 1 Why is the voltage at the generator boosted for the purpose of transmission? To minimize line losses. 2 How are voltages boosted and reduced? The voltage is boosted and reduced using transformer. 3 What are the common voltages used for the transmission system? 69KV—756KV 4 Other then for boosting and reducing voltages, what other purposes are transformers used for? Shifting power phase/ angle to regulate the power flow, isolation. 5 What kind of conductors are normally used in transmission lines? Aluminum Conductor (Steel reinforced) – ACSR 6 What are the types of tower structure materials used? Wood and steel. 7 How are faults and disturbances on the transmission system sensed? The fault and disturbance are sensed using relays. 8 How are faulted sections of the transmission system isolated? Switchgear (circuit breakers, disconnects, and fuses) 9 What devices are used to measure voltages and currents? Pot. Transformer and current transformers 10 What are FACTS devices? Flexible AC Transmission Systems (FACTS) are a group of devices which can improve transmission efficiency, control flow, improve stability of the system, etc. It contains thyristors, modular series capacitors, power angle regulators and dynamic load brakes. Distribution subsystem 1 What are the common voltage levels used in the distribution system? 110-34.5 KV 2 What are the two types of distribution systems commonly used? Overhead and underground distributed systems. 3 How are distribution systems isolated for repair and maintenance? Circuit breakers and/or switches are opened to de-energize the equipment. 4 What is the type of distribution system preferred in large urban cities? Underground distribution system is preferable. 5 What are the various means of controlling voltages in distribution systems? Capacitors, on-load tap changing transformers, and voltage regulators. 6 At what voltage is power delivered to residential customers? Typically, voltage is delivered to residential customers at 120/240 volts, single-phase. They may also receive 208/120 three-phase and 480/277 volts three-phase. 7 How are distribution circuits protected against faults and disturbances? Relays sense the fault based on decreased voltage and/or increased current and activate circuit breakers. Many distribution circuits are protected by fuses which respond to high currents caused by faults. 8 Are underground distribution systems more economical than overhead distribution systems? If not, why? Underground lines are typically less economical (more expensive) than overhead lines because underground systems require the conductors be (a) insulated from the ground and (b) insulated from each other. The close proximity of conductors in underground cable makes the cost of insulation very high. Also, it is generally more expensive to maintain an underground system. 9 Where is metering done to measure usage? Meters are placed on any load (residential, commercial, and industrial). 10 What does an on load tap changing transformer do? On load tap changing transformer change the turns ratio in the transformer which adjusts the voltage ratio. 2. Text, chapter 1 1.4 The transformer is one of the major inventions in power system. Why can’t we use it in the DC system? The transformer requires alternating magnetic fields to couple its two separate windings. The dc cannot generate such magnetic field. 1.5 State the advantage and disadvantage of using low voltage transmission lines. Disadvantage: Larger losses occur with low voltage. Advantage: They are less expensive to build. 1.6 State the advantage and disadvantage of using high voltage transmission lines. Advantage: Less power losses consumed during the transmission. Disadvantage: Facilities are more expensive. 3 Text, chapter 2 2.1 What is the function of a power plant turbine? Convert the thermal or the hydro kinetic energy into rotating mechanical energy that drives the generator. 2.2 What is the function of a power plant generator? To convert the mechanical energy of the turbine into electrical energy. 2.3 What is the function of hydro dam? To increase the potential energy of the water behind the dam. 2.4 Why transformers are used with transmission lines? To increase the voltage of the transmission lines, so current can be reduced. Thus the transmission lines can be made of small cross section wires. 2.7 Why insulators are used on power line towers? To isolate the conductor from the tower. 2.8 Why the tower insulators are built like disk shape? To increase the flashover distance between the conductor and the tower. 2.9 Why the frequency of the airplane power system is 400 Hz? To reduce the size of the magnetic components. 4 Text, chapter 4 4.1 Name three types of hydroelectric power plant. Impoundment, diversion and pumped storage. 4.2 Why are cooling towers used in thermal power plant? Heat sink, W=Q1-Q2. 4.3 What are the two nuclear reactions? Fission and fusion. 4.6 What is the major difference between boiling water reactors and the pressurized water reactors? Pressurized reactor has heat exchanger (steam generator) between the radioactive water and the steam entering the turbine. 5 Text, chapter 5 5.1 Name three types of major power. plants.Fossil, Hydro and Nuclear. 5.2 How is acid rain produced? Sulfur oxides and nitrogen oxides are absorbed by the clouds. 5.3 What is greenhouse effect? When excessive greenhouse gases are discharged in the atmosphere. They prevent the heat from escaping back to the outer space. 5.4 State four drawbacks of hydroelectric power plant. Flooding, silt buildup behind dam, lack of silt down steam, slow flow down steam, oxygen depletion, nitrogen absorption, fish migration. 6 Text, chapter 6 6.2 State 3 factors that determine the amount of power generated by wind machines. Sweep area (blade length), air density, and air velocity. 6.13 What are the different types of Fuel Cell? PEM (Proton Exchange Membrane), molten carbonate, alkaline, phosphoric acid, and solid oxide. 6.14 Which fuel cell type is suitable for high power? Phosphoric acid, molten carbonate and solid oxide. 6.23 What are the benefits of using geothermal energy? It is cleaner than fossil fuel plants. Geothermal fields produce only about one-sixth of the carbon dioxide that a natural-gas-fueled power plant, and little of nitrous oxide or sulfur-bearing gases. Geothermal energy is available 24 hours a day, 365 days a year. Geothermal power plants have average availabilities of 95% or higher, compared to 60%-70% for coal and nuclear plants. 6.27 What is biomass? Biomass is the organic matter produced by plants. 6.28 How electricity is generated from biomass? Direct combustion is the simplest and most common method of capturing the energy contained within biomass. Usually these facilities (boilers) produce steam to use either within an industrial process, or to produce electricity directly. They can also produce heat, which is then captured for one propose or another.