农业电气化专业英语试卷

农业电气化专业英语试卷集团文件发布号：（9816-UATWW-MWUB-WUNN-INNUL-DQQTY-专业英语一、词汇potential difference 电位差 frequency domain 频域Sinusoidal AC Circuit 正弦交流电路Three-Phase Circuit 平衡三相电路 D/A = Digital-to-Analog 数模变换On-State Losses 通态损耗Power Electronic Technology 电力电子技术transformer 变压器 synchronous motor 同步电动机permanent magnet 永久磁铁 horseshoe magnet 马蹄形磁铁exciting voltage 励磁电压 performance characteristics 工作特性audio signal 声频信号 instruction指令electric power system电力系统nominal frequency 额定频率 distribution system 配电系统二、英译汉1.Modern power systems are usually large-scale,geographically distributed, and with hundreds to thousands of generators operating in parallel and synchronously. They may vary in size and structure from one to another, but they all have the same basic characteristics：transmit power over significant distances to consumers spread over a wide area. This requires a transmission system comprising subsystems operating at different voltage levels.现代电力系统通常是规模大，地域分布广，具有成百上千并列同步运行的发电机组。

2.In spite of the initial widespread use of DC systems, theywere almost completely superseded by AC systems. By 1886, the limitations of DC systems were becoming increasingly apparent. They could deliver power only a short distance from generators. To keep transmission power losses (I2R) and voltage drops to acceptable levels, voltage levels had to be high for long-distance power transmission. Such high voltages were not acceptable for generation and consumption of power; therefore, a convenient means for voltage transformation became a necessity.3.Most people can formulate a mental picture of a computer,but computers do so many things and come in such a variety of shapes and sizes that it might seem difficult to distill their common characteristics into an all-purpose definition. At its core, a computer is a device that accepts input, processes data, stores data, and produces output, all according to a series of storedinstructions.4.Whereas the copper disk will rotate in the same directionas the rotating magnetic field, it will never reach the same speed as the rotating magnet, because if it did, there would be no relative motion between the two and therefore no current induced in the copper disk. The difference in speed between the rotating magnetic field and the copper disk is known as slip, which is essential to the operation of an induction motor.5.Switches i ncluding the diodes are assumed to be ideal andunidirectional, that is, they have zero on-state losses, zero off-state losses, zero switching losses and unrestricted voltage or current carrying capabilities.Switching devices in a practical design example must be selected with these desired characteristics in mind.Inductors, capacitors and transformers are assumed to be ideal.6.Power losses in the power electronic converters arecomprised of ①the switching losses and ②the parasitic losses. The parasitic losses account for the losses due to the winding resistances of the inductors and transformers, the dielectric losses of capacitors, theeddy and the hysteresis losses. The switching losses are significant and can be managed. They can be further divided into three components: (a) the on-state losses,(b) the off-state losses and ③the losses in thetransition states.7.The other kind of signal is a digital signal. A digitalsignal is one that can take on values within two discrete ranges. Such signals are used to represent ON-OFF or YES-NO information. An ordinary household thermostat deliversa digital signal to control the furnace. When the roomtemperature drops below a preset value, the thermostat switch closes turning on the furnace. Once the room temperature rises high enough, the switch opens turning off the furnace. The current through the switch providesa digital representation of the temperature variation: ONequals "too cold" while OFF equals "not too cold".8. A signal-processing system is an interconnection ofcomponents and devices that can accept an input signal ora group of input signals, operate on the signals in somefashion either to extract or improve the quality of the information, and present the information as an output in the proper form at the proper time.9. Ana lyzing AC circuit usually requires three steps.（1）Transform the circuit to the phasor or frequency domain.（2）Solve the problem using circuits techniques (nodal analysis, mesh analysis, superposition theorem etc.).（3）Transform the resulting phasor to the time domain.10. A typical three-phase system consists of three voltage sources connected to loads by three or four wires(ortransmission lines). A three-phase system is equivalent to three single-phase circuits. The voltage sources can be either wye-connected as shown in Fig.1-23(a) or delta-connected as in Fig.1-23(b).11. Fig.l-2 shows the voltage across an element (represented by a rectangular block) connected to points a and b. The plus (+) and minus (-) signs are used to define reference direction or voltage polarity. The uab can be interpreted in two ways: ①point a is at a potential of uab volts higher than point b; ②the potential at point a with respect to point b is uab. It follows logically that in general ab ba u u =- .三、 汉译英1. The increasing need for transmitting large amounts ofpower over longer distance created an incentive to use ab bau u =-progressively high voltage levels.日益增长的对远距离大容量功率输送的需求导致所使用的电压水平不断提高。