畢業(yè)設(shè)計三相異步電動機外文翻譯

1、中文翻譯異步電動機具有結(jié)構(gòu)簡單、運行可靠、價格低、維護方便等一系列的優(yōu)點,因此,異步電動機被廣泛應(yīng)用在電力拖動系統(tǒng)中。尤其是隨著電力電子技術(shù)的發(fā)展和交流調(diào)速技術(shù)的日益成熟,使得異步電動機在調(diào)速性能方面大大提高。目前,異步電動機的電力拖動已被廣泛地應(yīng)用在各個工業(yè)電氣自動化領(lǐng)域中。就三相異步電動機的機械特性出發(fā),主要簡述電動機的啟動,制動、調(diào)速等技術(shù)問題。1 三相異步電動機的機械特性文三相異步電動機的機械特性是指電動機的轉(zhuǎn)速n與電磁轉(zhuǎn)矩Tem之間的關(guān)系。由于轉(zhuǎn)速n與轉(zhuǎn)差率S有一定的對應(yīng)關(guān)系,所以機械特性也常用Tem=f(s的形式表示。三相異步電動機的電磁轉(zhuǎn)矩表達式有三種形式,即物理表達式、參數(shù)表達

2、式和實用表達式。物理表達式反映了異步電動機電磁轉(zhuǎn)矩產(chǎn)生的物理本質(zhì),說明了電磁轉(zhuǎn)矩是由主磁通和轉(zhuǎn)子有功電流相互作用而產(chǎn)生的。參數(shù)表達式反映了電磁轉(zhuǎn)矩與電源參數(shù)及電動機參數(shù)之間的關(guān)系,利用該式可以方便地分析參數(shù)變化對電磁轉(zhuǎn)矩的影響和對各種人為特性的影響。實用表達式簡單、便于記憶,是工程計算中常采用的形式。電動機的最大轉(zhuǎn)矩和啟動轉(zhuǎn)矩是反映電動機的過載能力和啟動性能的兩個重要指標(biāo),最大轉(zhuǎn)矩和啟動轉(zhuǎn)矩越大,則電動機的過載能力越強,啟動性能越好。三相異步電動機的機械特性是一條非線性曲線,一般情況下,以最大轉(zhuǎn)矩(或臨界轉(zhuǎn)差率為分界點,其線性段為穩(wěn)定運行區(qū),而非線性段為不穩(wěn)定運行區(qū)。固有機械特性的線性段屬于硬

3、特性,額定工作點的轉(zhuǎn)速略低于同步轉(zhuǎn)速。人為機械特性曲線的形狀可用參數(shù)表達式分析得出,分析時關(guān)鍵要抓住最大轉(zhuǎn)矩、臨界轉(zhuǎn)差率及啟動轉(zhuǎn)矩這三個量隨參數(shù)的變化規(guī)律。2 三相異步電動機的啟動小容量的三相異步電動機可以采用直接啟動,容量較大的籠型電動機可以采用降壓啟動。降壓啟動分為定子串接電阻或電抗降壓啟動、Y-D降壓啟動和自耦變壓器降壓啟動。定子串電阻或電機降壓啟動時,啟動電流隨電壓一次方關(guān)系減小,而啟動轉(zhuǎn)矩隨電壓的平方關(guān)系減小,它適用于輕載啟動。Y-D降壓啟動只適用于正常運行時為三角形聯(lián)結(jié)的電動機,其啟動電流和啟動轉(zhuǎn)矩均降為直接啟動時的1/3,它也適用于輕載啟動。自耦變壓器降壓啟動時,啟動電流和啟動轉(zhuǎn)

4、矩均降為直接啟動時的l/k2(k為自耦變壓器的變比,適合帶較大的負(fù)載啟動。繞線轉(zhuǎn)子異步電動機可采用轉(zhuǎn)子串接電阻或頻敏變阻器啟動,其啟動轉(zhuǎn)矩大、啟動電流小,適用于中、大型異步電動機的重載啟動。軟啟動器是一種集電機軟啟動、軟停車、輕載節(jié)能和多種保護功能于一體的新型電動機控制裝置,國外稱為Soft Starter。它的主要構(gòu)成是串接于電源與被控電動機之間的三相反并聯(lián)晶閘管及其電子控制電路。運用串接于電源與被控電動機之間的軟啟動器,以不同的方法,控制其內(nèi)部晶閘管的導(dǎo)通角,使電動機輸入電壓從零以預(yù)設(shè)函數(shù)關(guān)系逐漸上升,直至啟動結(jié)束,賦予電動機全電壓,即為軟啟動。在軟啟動過程中,電動機啟動轉(zhuǎn)矩逐漸增加,轉(zhuǎn)速

5、也逐漸增加。軟啟動器實際上是個調(diào)壓器,用于電動機啟動時,輸出只改變電壓并沒有改變頻率。3 三相異步電動機的調(diào)速三相異步電動機的調(diào)速方法有變極調(diào)速、變頻調(diào)速和變轉(zhuǎn)差率調(diào)速。其中變轉(zhuǎn)差率調(diào)速包括繞線轉(zhuǎn)子異步電動機的轉(zhuǎn)子串接電阻調(diào)速、串級調(diào)速和降壓調(diào)速。變極調(diào)速是通過改變定子繞組接線方式來改變電機極數(shù),從而實現(xiàn)電機轉(zhuǎn)速的變化。變極調(diào)速為有級調(diào)速,變極調(diào)速時的定子繞組聯(lián)結(jié)方式有三種:Y-YY、順串Y-反串Y、D-YY。其中Y-YY聯(lián)結(jié)方式屬于恒轉(zhuǎn)矩調(diào)速方式,另外兩種屬于恒功率調(diào)速方式。變極調(diào)速時,應(yīng)同時對調(diào)定子兩相接線,這樣才能保證調(diào)速后電動機的轉(zhuǎn)向不變。變頻調(diào)速是現(xiàn)代交流調(diào)速技術(shù)的主要方向,它可實現(xiàn)

6、無級調(diào)速,適用于恒轉(zhuǎn)矩和恒功率負(fù)載。繞線轉(zhuǎn)子電動機的轉(zhuǎn)子串接電阻調(diào)速方法簡單,易于實現(xiàn),但調(diào)速是有級的,不平滑,且低速時特性軟,轉(zhuǎn)速穩(wěn)定性差,同時轉(zhuǎn)子銅損耗大,電動機的效率低。串級調(diào)速克服了轉(zhuǎn)子串接電阻調(diào)速的缺點,但設(shè)備要復(fù)雜得多。異步電動機的降壓調(diào)速主要用于風(fēng)機類負(fù)載的場合,或高轉(zhuǎn)差率的電動機上,同時應(yīng)采用速度負(fù)反饋的閉環(huán)控制系統(tǒng)。把電壓和頻率固定不變的工頻交流電變換為電壓或頻率可變的交流電的裝置稱作“變頻器”。為了產(chǎn)生可變的電壓和頻率,該設(shè)備首先要把電源的交流電變換為直流電(DC,這個過程叫整流。再把直流電(DC變換為交流電(AC,這個過程叫逆變,把直流電變換為交流電的裝置叫逆變器(inv

7、erter。對于逆變?yōu)轭l率可調(diào)、電壓可調(diào)的逆變器我們稱為變頻器。變頻器輸出的波形是模擬正弦波,主要用在三相異步動機的調(diào)速,又叫變頻調(diào)速器。附錄二外文原文Asynchronous motor has a simple structure, reliable operation, low price, convenient maintenance and a series of advantages, therefore, asynchronous motor is widely used in electric drive system. Especially with the developm

8、ent of power electronic technology and AC drive technology becomes more mature, greatly improve the speed performance makes the asynchronous motor. At present, electric drive asynchronous motor has been widely used in various industrial electrical automation. The mechanical properties of three-phase

9、 asynchronous motor starting, the main motor starting, braking, speed control technology.The mechanical properties of 1 three-phase asynchronous motorMechanical characteristics of three-phase asynchronous motor is refers to the relationship between the speed of the motor electromagnetic torque of N

10、and Tem. Due to the speed of N and slip S have a certain relationship, so the mechanical properties are also commonly used Tem = f (s representation. Electromagnetic torque expression of three-phase asynchronous motor has three forms, namely physical expression, parameters and practical expression.

11、Physical expressions reflect the physical nature of electromagnetic torque of asynchronous motor, the electromagnetic torque is generated by the main flux and rotor active current interaction. Parameter expression reflects the relationship between parameters of electromagnetic torque and power suppl

12、y parameters and motor, the expression can be used to influence easily analyze the influence of parameter variation on the electromagnetic torque and all kinds of human characteristics. Practical expressions in a simple, easy to remember, is often used in engineering calculation in the form of.The m

13、aximum torque of motor and torque are two important indexes reflecting the overload capacity of the motor and starting performance, maximum torque and start torque motor overload capacity is bigger, stronger, better starting performance.The mechanical characteristic of three-phase asynchronous motor

14、 is a nonlinear curve, under normal circumstances, with the maximal torque (or critical slip as a cutoff point, the linear segment for the stable operation region, while the nonlinear section is not stable operating region. Hard characteristic is linear segment inherent mechanicalproperties, the nom

15、inal operating point speed slightly lower than the synchronous speed. Shape parameters available expressions man-made mechanical characteristic curve analysis, analysis the key to grasp the maximum torque, starting torque variation of critical slip and the three with the parameters of.2 three-phase

16、asynchronous motor startingThree-phase asynchronous motor with small capacity can be used to directly start, cage motor with large capacity can adopt step-down start. Step-down start into stator resistance or reactance step-down start, Y-D step-down start and autotransformer start. The stator resist

17、ance or motor step-down start, starting current voltage relations with a reduced, and the starting torque with the square of the voltage is reduced, it is suitable for the starting load. Only applicable to motor start to normal operation for the triangle connection Y-D buck, the starting current and

18、 starting torque is reduced to direct startup 1/3, which is also suitable for the starting load. Autotransformer start, starting current and starting torque is reduced to direct startup l/k2 (k is the self coupling transformer, suitable for large load starting.The wound rotor asynchronous motor with

19、 rotor series resistance or frequency sensitive rheostat starting, the starting torque, small starting current, suitable for heavy load starting, large asynchronous motor.The soft starter is a novel control device for motor motor soft start, soft stop, light load energy saving and various protecting

20、 functions in one, called Soft Starter. The main structure is connected in series between the power supply and the controlled motor three-phase inverse parallel thyristor and its electronic control circuit. Through the series of soft starter is connected between the power supply and the controlled m

21、otor, in different ways, its internal control thyristor conduction angle, so that the motor input voltage from zero to a preset function gradually rise, until the end of the motor start, give full voltage, namely soft start. In the soft start-up process, starting torque motor speed increases gradual

22、ly, gradually increasing. The soft starter is actually a regulator, for when the motor is started, the output voltage does not change the frequency change.3 speed of three-phase asynchronous motorControl method of the three-phase asynchronous motor with variable speed, variable speed and variable sl

23、ip speed. The variable slip ratio control includes a rotor winding rotor asynchronous motor series resistance speed control, cascade control and blood pressure control.Variable speed is by changing the stator winding connection mode to change thepole number, so as to realize the change of motor spee

24、d. Variable speed is speed-regulation, variable stator winding connection speed of three kinds: Y-YY, Y-, D-YY and Y run. The Y-YY connection is constant torque speed control mode, another two species belong to the constant power control mode. Variable pole speed, should also be on the stator two-phase wiring, so that we can guarantee the speed regulation motor steering. Variable frequency speed control