农业电气化专业英语试卷

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, they were 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completely superseded by AC systems.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 voltagedropsto 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 stored instructions.

4. Whereas the copper disk will rotate in the same direction as 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 including the diodes are assumed to be ideal and unidirectional,

that is, they have zero on-state losses, zero off-state losses, zero switching

losses and unrestricted voltage or current carryingcapabilities. 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 are comprised 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, the eddy 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 the transition states.

7. The other kind of signal is a digital signal. A digital signal 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 delivers a digital signal tocontrol the furnace. When the room temperature 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 provides a digital representation of the temperature variation: ON equals \cold\

8. A signal-processing system is an interconnection of components and devices

that can accept an input signal or a group of input signals, operate on the signals in some fashion 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. Analyzing AC circuit usually requires three steps.

（1）Transform the circuit to the phasor or frequency domain.

ab??ubatechniques (nodal analysis, mesh （2）Solve the problem using ucircuits

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(or transmission 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 generaluab??uba.

三、 汉译英

1. The increasing need for transmitting large amounts of power over longer

distance created an incentive to use 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。

2. The series of instructions that tell a computer how to carry out processing

tasks is referred to as a computer program, or simply a \

告诉计算机如何执行处理任务的一系列指令被称为计算机程序，简称为程序。

3. Charge is an electrical property of the atomic particles of which matter

consists, measured in coulombs (C).

电荷是构成物质的原子的电气属性，其量纲为库仑。

原题：1. Electrical loads can be of three types: impedance load, AC voltage sink load or AC current sink load. Examples of impedance load are electromagnetic ac relays, electromagnetic pick up and lift equipments. The load comprises of a large value inductor. Examples of ac voltage sink are the constant speed drives for induction and synchronous motors. Examples of AC current sink are constant torque drives for the induction and synchronous motors.

2. The various logic gates and their interconnections can be made to perform all the essential functions required for computing and decision-making. In developing digital systems the easiest procedure is to put together conceptually the gates and connections to perform the assigned task in the most direct way. Boolean algebra is then used to reduce the complexity of the system, if possible, while retaining the same function. The equivalent simplified combination of gates will probably be much less expensive and less difficult to assemble.