《电气工程英语》课程教学资源（课文）U3 Electric Power Systems.pdf_大学文库

Electric Power Systems Text A An electric power system is a network of electrical components deployed to supply. transfer,and use electric power.An example of an electric power system is the network that supplies a region's homes and industry with power-for sizeable regions,this power system is known as the grid and can be broadly divided into the generators that supply the power,the transmission system that carries the power from the generating centres to the load centres and the distribution system that feeds the power to nearby homes and industries.Smaller power systems are also found in industry,hospitals, commercial buildings and homes.The majority of these systems rely upon three-phase AC power-the standard for large-scale power transmission and distribution across the modem world.Specialised power systems that do not always rely upon three-phase AC power are found in aircraft,electric rail systems,ocean liners and automobiles 2 All power systems have one or more sources of power.For some power systems,the source of power is external to the system but for others it is part of the system itself. DC power can be supplied by batteries,fuel cells or photovoltaic cells.AC power is typically supplied by a rotor that spins in a magnetic field in a device known as a turbo generator.There have been a wide range of techniques used to spin a turbine's rotor,from steam heated rotor using fossil fuel (including coal,gas and oil)to nuclear energy,falling water(hydroelectric power)and wind(wind power). Power systems deliver energy to loads that perform a function.These loads range from household appliances to industrial machinery.Most loads expect acerain voltage and, forACdevicesern frequency and number of phases The appiances found inyour home,for example,will typically be single-phase operating at 50 or 60 Hz with a voltage between 110 and 260 volts(depending on national standards).An exception exists for centralized air conditioning systems,as these are now typically three-phase because thisallows themtooperate more efficeyAll devicesnyououse will alsohavea wattage,which specifies the amount of power the device consumes.At any one time, the net amount of power consumed by the loads on a power system must equal the net amount of power produced by the supplies less the power lost in transmission Unit 3 A Glimpse of Electric Power Systems 45

Electri .c Power Systems 1 An electric power system is a network of electrical components deployed to supply, transfer, and use electric power. An example of an electric power system is the network that supplies a region's homes and industry with -power - for sizeable regions, this power system is known as the grid and can be broadly divided into the generators that supply the power, the transmission system that carries the power from the generating centres to the load centres and the distribution system that feeds the power co nearby homes and industries. Smaller power systems are also found in industry, hospitals, , commercial buildings .and homes. The majority of these systems rely upon three-phase AC power - the standard for large-scale power transmission and distribution across the modern world. Specialised power stems that do not always rely upon three-phase AC power are found in aircraft, electric rail systems, ocean liners and automobiles. 2 All power systems have one or more sources of power. For some power systems, the source of power is external to the system but for others it is part of the system itself. DC power can be supplied by batteries, fuel cells or photovoltaic cells. AC power is typically supplied by a rotor that spins in a magnetic field in a device known as a turbo generator. There have been a wide range of techniques used to spin a turbine's rotor, from steam heated rotor using fossil fuel (inclu coal, gas and oil) to nuclear energy, falling water(hydroelectric power) and wind (wind power). J Power systems deliver energy to loads that perform a function. These loads range from household appliances to industrial machinery. Most loads expect a certain voltage and, for AC devices, a certain frequency and number of phases. The appliances found in your home, for example, will typically be single-phase opera at 50 or 60 Hz with a voltage between 110 and 260 volts (depending on national standards). An exception exists for centra ed con tioning systems, as these are now typically three-phase because allows them to operate more efficiently. All devices in your house will also have a wattage, which speci:fies the amount of power the device consumes. At any one time, the net amount of power conswned by the loads on a power system must equal the net amount of power produced by the supplies less the power lost in transmission. Unit 3 A Glimpse of Electric Power Systems 45

4 Conductors carry power from the generators to the load.In a grid,conductors may be classified as belonging to the transmission system,which carries large amounts of power at high voltages(typically more than 69 kV)from the generating centres to the load centres,or the distribution system,which feeds smaller amounts of power at lower voltages(typically less than 69 kV)from the load centres to nearby homes and industry. s Choice of conductors is based upon considerations such as cost,transmission losses and other desirable characteristics of the metal,like tensile strength. Copper,with lower resistivity than Aluminum,was the conductor of choice for most power systems.However,Aluminum has lower cost for the same current carrying capacity and is the primary metal used for transmission line conductors Overhead line conductors may be reinforced with steel or aluminum alloys. Electricity grid systems connect multiple generators and loads operating at the same frequency and number of phases,the commonest being three-phase at 50 or 60 Hz.However,there are other considerations.These considerations range from the obvious:How much power should the generator be able to supply; What is an acceptable length of time for starting the generator(some generators can take hours to start);Is the availability of the power source acceptable(some renewables are only available when the sun is shining or the wind is blowing): to the more technical:How should the generator start;What is the mechanical speed of operation for the turbine and consequently what is the number of poles required;What type of generator is suitable(synchronous or asynchronous) and what type of rotor(squirrel-cage rotor,wound rotor,salient pole rotor or cylindrical rotor)is appropriate? Electric power is the product of two quantities:current and voltage.These two quantities can vary with respect to time(AC power)or can be kept at constant levels(DC power).Solid state devices,which are products of the semiconductor revolution,make it possible to transform DC power to different voltages,build brushless DC machines and convert between AC and DC power. Nevertheless,devices utilizing solid state technology are often more expensive than their traditional counterparts,so AC power remains in widespread use. 46电气工程英语

46 4 Conductors carry power from the generators to the load. In a grid, conductors may be classified as belonging to the transmission system, which carries large amounts of power at high voltages (typically more than 69 kV) from the generating centres to the load centres, or the distribution system, which feeds smaller amounts of power at lower voltages (typically less than 69 kV) from the load centres to nearby homes and industry. s Choice of conductors is based upon considerations such as cost, transmission losses and other desirable characteristics of the metal, like tensile strength. Copper, with lower resistivity than Aluminum, was the conductor of choice for most power systems. However, Alun um has lower cost for the srune current ca ing capacity and is the primary metal used for transmission line conductors. Overhead line conductors may be reinforced with steel or aluminum alloys. 6 Electricity grid systems connect multiple generators and loads operating at the same frequency and number of phases, the commonest being three-phase at 50 or 60 Hz. However, there are other considerations. These considerations range from the obvious: How much power should the generator be able to supply; What is an acceptable length of time for starting the generator (some generators can take hours to start); Is the availability of the power source acceptable (some rencwables are only available when the sun is shining or the wind is blowing); to the more technical: How should the generator start; What is the mechanical speed of operation for the turbine and consequently what is the number of poles · required; What type of generator is suitable (synchronous or asynchronous) and what type of rotor (squirrel-cage rotor, wound rotor, salient pole rotor or cylin cal rotor) is appropriate? 1 Electric power is the product of two quantities: current and voltage. These 电气工程英语 two quantities can vary with respect to time (AC power) or can be kept at constant levels(DC powerJ. Solid state devices, which are products of the semiconductor revolution, make it possible to transform DC power to different voltages, build brushless DC machines and convert between AC and DC power. Nevertheless, devices utilizing solid state technology are often more expensive than their traditional counterparts, so AC power remains in widespread use