陕西科技大学电气专业英语试卷

Exercise 2一、阅读理解（20points ）: Passage one The circuit element used to model the current-resisting behaviorof a material is the ① . It is the simplest ② element. George Simon Ohm is credited with formulating the ③relationship for a resistor based on experiments performed in 1826.This relationship is known as Ohm's Law. Ohm's Law states that the voltage across a resistor is ④ the current flowing through the resistor. The constant of proportionality is the resistance value of the resistor in ohms. The circuit symbol for the resistor is shown in Fig.1. For the current and voltage shown, Ohm's Law isu(t) = Ri(t) (1)where R≥0 is the resistance in ohms.Since R is constant, Eq.(1) is the equation of a straight line. For this reason, the resistor is called a linear resistor. A graph of u(t) versus i(t) for a linear resistor is a line passing through the origin with a slope of R.Resistors whose resistances do not remain constant for different terminal current are known as ⑤ resistors. For such a resistor, the resistance is a function of the current flowing in the device. In reality, all practical resistors are nonlinear because the electrical characteristics of all conductors are affected by environmental factors such as temperature. Many materials, however, closely approximate an ideal linear resistor over a desired operating region.Choose the best answer into the blanks.1 A. capacitor B. inductoru (t )i (t ) + _Fig.1C. resistorD. source2 A. passive B. activeC. linearD. nonlinear3 A. current-current B. current-voltageC. voltage-powerD. current-power4 A. equal to B. directly proportional toC. inversely proportional toD. different from5 A. linear B. constantC. nonlinearD. time-varyingPassage twoThe effective value of voltage and current is the common method of expressing the Value of AC. This is also known as the RMS value. The effective value of AC is defined in terms of an equivalent heating effect when compared to DC. One RMS ampere of current flowing through a resistance will produce heat at the same rate as a DC ampere. For purpose of circuit design, the peak value may also be needed. For example, insulation must be designed to withstand the peak value, not just the effective value. It may be that only the effective value is known. To calculate the peak value, multiply the effective value by 1.41.6.Which equation is true?( )A.V peak×1.41=V rmsB. V peak÷0.707=V rmsC. V peak×0.707=V rms7.According to the passage, if the effective value is 100V, the peak value is( ).A 141B 70.9C 70.7D 14.1 Passage threeHowever, it is usually adequate to sample a signal at twice its highest frequency. Each binary digit used to show a binary value is known as a bit. The accuracy of conversion is limited by the number of binary bits used by the ADC . If the conversion is made using a four-bit ADC, only sixteen different binary values can be produced. The smallest value is 0000 and the largest is 1111. If an 8-bit ADC is used, then 256 different digital values can be produced. When a measurement of the analogue signal does not coincide with one of these binary values, it must be rounded up or down.8. If the analogue signal is u=sin(200πt), then the adequate sampling frequency must be more than .A 50Hz. B. 100Hz C. 200Hz D. 50πHz9. If the conversion is made using a ten-bit ADC, different binary values can be produced.A.1024.B. 256C. 512D. 1010. Explain the underlining word in Chinese according to the article.rounded up or down ( )二、学术词组或句子翻译(20points)：⑴有源滤波器⑵机电能量转换⑶不间断电源⑷模数转换器⑸接地故障⑹状态变量⑺中性点⑻差动继电保护⑼绝缘配合⑽局部放电⑾有功功率⑿操作中，与交流供电相连的是一次绕组，与负载相连的是二次绕组。

⒀我们的工作是使电力从它可以取得的地方输送到需用电力的地方去，输电损失要尽可能小。

⒁本文讨论固态功率器件及其在三相交流感应电机中的应用。

三、根据英文意思找出合适的单词（从列出的单词）（10points）equipotential; inertia; neutral,; short circuit; circuit breaker; lightning;prevent; actuate; carry; customers; cable; contact; relay; increased;armature; protect; power; electricity; rely on; drop out; instantaneous;generator; bearing, magnetic flux(1).A device that responds to a small current or voltage change by activatingswitches or other devices in an electric circuit.（）(2).The tendency of a body to resist acceleration; the tendency of a body at rest toremain at rest or of a body in motion to stay in motion in a straight line unless acted on by an outside force.（）(3).A device that supports, guides, and reduces the friction of motion betweenfixed and moving machine parts.（）(4).The rotating part of a dynamo, consisting essentially of copper wire woundaround an iron core.（）(5).A measure of the quantity of magnetism, being the total number of magneticlines of force passing through a specified area in a magnetic field.（）(6).One that generates, especially a machine that converts mechanical energy intoelectrical energy.（）(7).An automatic switch that stops the flow of electric current in a suddenlyoverloaded or otherwise abnormally stressed electric circuit.（）(8).Of or relating to a particle, an object, or a system that has a net electric chargeof zero.（）(9).A low-resistance connection accidentally established between two points in anelectric circuit.（）(10).Having the same electric potential at every point.（）四、英译汉（35points）Passage oneWhen two or more synchronous machines are interconnected, the stator voltages and currents of all the machines must have the same frequency and the rotor mechanical speed of each is synchronized to this frequency. Therefore, the rotors of all interconnected machines must be in synchronism. In a generator, the electromagnetic torque opposes rotation of the rotor, so that mechanical torque must be applied by the prime mover to sustain rotation. The electrical torque (or power) output of the generator is changed only by changing the mechanical torque input by the prime mover. The effect of increasing the mechanical torque input is to advance the rotor to a new position relative to the revolving magnetic field of the stator. Conversely, a reduction of mechanical torque or power input will retard the rotor position. In a synchronous motor, the roles of electrical and mechanical torques arereversed compared to those in a generator.Passage twoDistribution substations change the medium voltage to low voltage by means of step-down transformers, which may have automatic tap-changing capabilities to regulate the low voltage. The low voltage ranges from 120/240 single phase to 600v, 3-phase. It serves to power private residences, commercial and institutional establishments, and small industry. These substations also contain circuit breakers, fuses, and lighting arresters, to protect expensive apparatus, and to provide for quick isolation of faulted lines from the system. In addition, control apparatus, power-measuring devices, disconnect switches, capacitors, inductors, and other devices may be part of a substation.Passage threePower systems are often subjected to overvoltages that have their origin in atmospheric discharges in which case they are called external or lightning overvoltages, or they are generated internally by connecting or disconnecting the system, or due to the systems fault initiation or extinction. The latter type is called internal overvoltage4. This class may be further subdivided into (1) temporary overvoltages, if they are oscillatory of power frequency or harmonics, and (2) switching overvoltages, if they are heavily damped and of short duration. Temporary overvoltages occur almost without exception under no load or very light load conditions. Because of their common origin the temporary and switching overvoltages occur together and their combined effect has to be taken into account inthe design of H.V. systems insulation.Passage fourSimulation and Experimental Study Of Interharmonic Performance of aCycloconverter-fed Synchronous Motor Drive Abstract—High-power synchronous motor drives are usually fed from naturally commutated cycloconverters. The output voltage of the cycloconverter contains interharmonics/subharmonics which affect the power quality and restrict the allowable frequency range. Further, a practical circulating current-free cycloconverter usually gives rise to stator current discontinuities. The present paper deals with a simulation method to study the performance of a cycloconverter-fed synchronous motor drive in the presence of interharmonics/subharmonics taking into account the discontinuities in the output current as well as the effect of ripple in the output current on the input current of the cycloconverter. Interharmonics in output phase voltage, output phase current, input supply current, and the field current are estimated and verified with experimental results on a laboratory prototype. The significant oscillating torque components due to these interharmonics are identified in a typical case. The simulation results are useful in power quality studies for such drives and in devising methods for suppression of these interharmonics/subharmonics.五、写作（15points）1. 写出下图中各元部件的英文名称；2. 用英文描述下图所示的工作原理（100words以上）。