外文翻譯----感應(yīng)電機(jī)

1、<p><b>　　附錄A：外文資料</b></p><p>　　Induction Motor</p><p>　　1 Starting an induction motor</p><p>　　High-inertia loads put strain induction motors because they prolong t

2、he starting period. The starting current in both the stator and rotor is high during this interval so that overheating becomes a major problem. For motors of several thousand horsepower, a prolonged starting period may e

3、ven overload the transmission line feeding the plant where the motor is installed. The line voltage may fall below normal for many seconds, thus affecting other connected loads. To relieve the problem, induction</p>

4、;<p>　　Rule I - The heat dissipated in the rotor during the starting period (from zero speed to final rated speed) is equal to the final kinetic energy stored in all the revolving parts.</p><p>　　This

5、 rule holds true, irrespective of the stator voltage or the torque-speed curve of the motor. Thus, if a motor brings a massive flywheel up to speed, and if the energy stored in the flywheel is then 5000 joules. the rotor

6、 will have dissipated 5000 joules in the form of heat. Depending upon the size of the rotor and its cooling system, this energy could easily produce overheating.</p><p>　　2 Plugging an induction motor</p&

7、gt;<p>　　In some industrial applications, the induction motor and its load have to be brought to a quick stop. This can be done by interchanging two stator leads, so that the revolving field suddenly turns in the

8、opposite direction to the rotor. During this plugging period, the motor acts as a brake.</p><p>　　It absorbs kinetic energy from the still-revolving load, causing its speed to hill. The associated mechanical

9、 power P, is entirely dissipated as heat in the rotor. Unfortunately, the rotor also continues to receive electromagnetic power P from the stator, which is also dissipated as heat (Fig. 14.10). Consequently, plugging pro

10、duces 12R losses in the rotor that even exceed those when the rotor is locked. Motors should not he plugged too frequently because high rotor temperatures may melt the rot</p><p>　　Rule 2- The heat dissipate

11、d in the rotor during the plugging period (initial rated speed to zero speed) is three times the original kinetic energy of all the revolving parts.</p><p>　　Fig. 14.10</p><p>　　When a 3-phase i

12、nduction motor is plugged, the rotor losses are very high.3 Braking with direct current An induction motor and its high-inertia load can also be brought to a quick stop by circulating dc current in the stator winding. An

13、y two stator terminals can be connected to the dc source.</p><p>　　The direct current produces stationary N, S poles in the stator. The number of poles created is equal to the number of poles which the motor

14、 develops normally. Thus, a 3-phase, 4-pole induction motor produces 4 dc poles, no matter how the motor terminals are connected to the dc source.</p><p>　　When the rotor sweeps past the stationary field, an

15、 ac voltage is induced iii the rotor bars. The voltage produces an ac current and the resulting rotor losses are dissipated at the expense of the kinetic energy stored in the revolving parts. The motor finally comes to r

16、est when all the kinetic energy has been dissipated as heat in the rotor.</p><p>　　The advantage of dc braking is that it produces far less heat than does plugging. In effect, the energy dissipated in the ro

17、tor is only equal to the original kinetic energy stored in the revolving masses, and not three times that energy. The energy dissipated in the rotor is independent of the magnitude of the dc current. However, a smaller d

18、c current increases the braking time. The dc current can be two or three times the rated current of the motor. Even larger values can be used, provided that</p><p>　　4 Abnormal conditions</p><p>

19、;　　Abnormal motor operation may due to internal problems (short-circuit in the stator, overheating of the bearing, etc. ) or to external conditions. External problems may be caused by any of the following:</p><

20、;p>　　1. Mechanical overload</p><p>　　2. Supply voltage changes </p><p>　　3. Single phasing</p><p>　　4. Frequency changes</p><p>　　We will examine the nature of these

21、 problems in the sections that follow.</p><p>　　According to national standards, a motor shall operate satisfactory on any voltage within ± 10% of the nominal voltage, and for any frequency within ±

22、;5% of the normal frequency. If the voltage and frequency both vary, the sum of the two percentage changes must not exceed 10 percent. Finally, all motors are designed to operate satisfactorily at altitudes up to 1000 m

23、above sea level. At higher altitudes the temperature may exceed the permissible limits due to the poor cooling afforded by the thin</p><p>　　5 Mechanical overload</p><p>　　Although standard indu

24、ction motors can develop as much as twice their rated power for short periods, they should not be allowed to run continuously beyond their rated capacity. Overloads cause overheating, which deteriorates the insulation an

25、d reduces the service life of the motor. In practice the overload causes the thermal overload relays in the starter box to trip. bringing the motor to a stop before its temperature gets too high.</p><p>　　So

26、me drip-proof motors are designed to carry a continuous overload of I 5 percent. This overload capacity is shown on the nameplate by the service factor 1.15. The allowable temperature rise is then 10°C higher than t

27、hat permitted for drip-proof motors operating at normal load.</p><p>　　During emergencies a drip-proof motor can be made to carry overloads as much as 125 percent, as long as supplementary external ventilati

28、on is provided. This is not recommended for long periods because even if the external frame is cool, the temperature of the windings may be excessive.</p><p>　　6 Line voltage changes</p><p>　　Th

29、e most important consequence of a line voltage change is its effect upon the torque-speed curve of the motor. In effect, the torque at any speed is proportional to the square of the applied voltage. Thus, if the stator v

30、oltage decreases by 10%, the torque at every speed will drop by approximately 20%. A line voltage drop is often produced during start-up, due to the heavy starting current drawn from the line. As a result of the lower vo

31、ltage, the starting torque may he much less than its rated</p><p>　　On the other hand, if the line voltage is too high when the motor is running, the flux per pole will be above normal. For a motor running a

32、t full-load, this increases both the ion losses and the magnetizing current, with the result that the temperature increases slightly and the power factor is slightly reduced.</p><p>　　If the 3-phase voltages

33、 are unbalanced, they can produce a serious unbalance of the three line currents. This condition increases the stator and rotor losses, yielding a higher temperature. A voltage Unbalance of as little as 3.5% can cause th

34、e temperature to increase by 15°C. The utility company should be notified whenever the phase-to-phase line voltages differ by more than 2 percent.</p><p>　　7 Single-phasing</p><p>　　If one

35、line of a 3-phase line is accidentally opened or if a fuse blows while the 3-phase motor is running, the machine wilt continue to run as a single-phase motor. The current drawn from the remaining two tines will almost do

36、uble, and the motor will begin to overheat. The thermal relays protecting the motor will eventually trip the circuit-hrC1’ hereby disconnecting the motor from the line.</p><p>　　The torque-speed curve is ser

37、iously affected when a 3-phase motor operates on single phase. The break- down torque decreases to about 40% of its original value, and the motor develops no starting torque at all. Consequently, a fully loaded 3-phase m

38、otor may simply stop if one of its lines is suddenly opened. The resulting locked-rotor current is about 90% of the normal 3-phase LR current. It is therefore large enough to trip the circuit breaker or to blow the fuses

39、.</p><p>　　Figure 14.11 Typical torque-speed curves when a 3-phase squirrel-cage motor operates normally and when it operates on single-phase.</p><p>　　Fig.14.11 shows the typical torque-speed c

40、urves of a 3-phase motor when it runs normally and when it is single-phasing. Note that the curves follow each other closely until the torque approaches the single-phase breakdown torque.</p><p>　　8 Frequenc

41、y variation</p><p>　　Important frequency changes never take place on a large distribution system, except during a major disturbance. However, the frequency may vary significantly on isolated systems where el

42、ectrical energy is generated by diesel engines or gas turbines. The emergency power supply in a hospital, the electrical system on a ship, and the generators in a lumber camp, are examples of this type of supply.</p&g

43、t;<p>　　The most important consequence of a frequency change is the resulting change in motor speed: if the frequency drops by 5%, the motor speed drops by 5%.</p><p>　　Machine tools and other motor-d

44、riven equipment imported from countries where the frequency is 50 Hz may cause problems when they are connected to a 60 Hz system. Everything runs 20% faster than normal, and this may not be acceptable in some applicatio

45、ns. In such cases we either have to gear down the motor speed or supply an expensive auxiliary 50 Hz source.</p><p>　　A 50 Hz motor operates well on a 60 Hz line, but its terminal voltage should be raised to

46、 6/5 (or I 20%) of the nameplate rating. The new breakdown torque is then equal to the original breakdown torque and the starting torque is only slightly reduced. Power factor, efficiency, and temperature rise remain sat

47、isfactory.</p><p>　　A 60 Hz motor can also operate on a 50 Hz line, but its terminal voltage should be reduced to 5/6 (or 83%) of its nameplate value. The breakdown torque and starting torque are then about

48、the same as be- fore, and the power factor, efficiency, and temperature rise remain satisfactory.</p><p><b>　　附錄B：中文翻譯</b></p><p><b>　　感應(yīng)電機(jī)</b></p><p><b&

49、gt;　　1 感應(yīng)電機(jī)的啟動(dòng)</b></p><p>　　高慣性負(fù)載由于其延長(zhǎng)了啟動(dòng)時(shí)間，所以會(huì)拖累感應(yīng)電機(jī)。啟動(dòng)時(shí)定子和轉(zhuǎn)子中的啟動(dòng)電流都很高，故過(guò)熱成為了感應(yīng)電機(jī)啟動(dòng)的主要問(wèn)題。比如一個(gè)幾千馬力的電機(jī)，因啟動(dòng)時(shí)間的延長(zhǎng)甚至?xí)寡b載電機(jī)設(shè)備的饋電回路過(guò)載。線電壓會(huì)低于正常值好幾秒鐘時(shí)間，因此影響到其他相連的負(fù)載。為了解決這個(gè)問(wèn)題，感應(yīng)電機(jī)經(jīng)常在低電壓下進(jìn)行啟動(dòng)。這樣就減少了電機(jī)的電力牽引，并以此降低

50、了線電壓的壓降和繞組上產(chǎn)生熱量的速度。雖然低電壓加長(zhǎng)了啟動(dòng)時(shí)間，但這一般來(lái)說(shuō)并不重要。對(duì)于一個(gè)無(wú)機(jī)械性加載電機(jī)來(lái)說(shuō)，無(wú)論啟動(dòng)時(shí)間是長(zhǎng)是短，記住下列規(guī)則是很有用的：</p><p>　　規(guī)則1：在啟動(dòng)過(guò)程中（從零速度到額定速度）在轉(zhuǎn)子上消耗的熱量相當(dāng)于最終所有旋轉(zhuǎn)部分所儲(chǔ)存的電能。</p><p>　　不管電機(jī)的定子電壓或者轉(zhuǎn)矩的大小，這個(gè)規(guī)則都是成立的。因此，如果一個(gè)電機(jī)要帶動(dòng)一個(gè)大型轉(zhuǎn)速

51、輪達(dá)到預(yù)定速度并且使該轉(zhuǎn)速輪所帶的動(dòng)能達(dá)到5000焦耳，那么轉(zhuǎn)子將以熱能的形勢(shì)消耗5000焦耳。取決于轉(zhuǎn)子的大小和冷卻系統(tǒng)的好壞，這些能量會(huì)很容易導(dǎo)致過(guò)熱。</p><p><b>　　2 感應(yīng)電機(jī)的制動(dòng)</b></p><p>　　在一些工業(yè)上的應(yīng)用中，感應(yīng)電機(jī)和它的負(fù)載需要在瞬間停止。這可以通過(guò)相互交換定子的兩個(gè)引線來(lái)實(shí)現(xiàn)，一旦交換，旋轉(zhuǎn)場(chǎng)馬上轉(zhuǎn)變?yōu)橄鄬?duì)轉(zhuǎn)子旋轉(zhuǎn)的

52、反方向。在這個(gè)制動(dòng)過(guò)程當(dāng)中，電機(jī)充當(dāng)了剎車閘的作用。</p><p>　　電機(jī)吸收了仍在旋轉(zhuǎn)負(fù)載的動(dòng)能，使它自己的速度降了下來(lái)。相關(guān)的機(jī)械能Pm在轉(zhuǎn)子當(dāng)中完全地耗盡。遺憾的是，轉(zhuǎn)子仍然從定子接收電磁能量Pr，這些能量也以熱能的形式發(fā)散。因此，制動(dòng)在轉(zhuǎn)子上產(chǎn)生了的消耗，在轉(zhuǎn)子被鎖住的時(shí)候甚至超過(guò)了這個(gè)值。電機(jī)不能被頻繁地制動(dòng)，因?yàn)檗D(zhuǎn)子的高溫會(huì)熔化轉(zhuǎn)子鐵片或者使定子線圈過(guò)熱?？紤]到這些，有必要記住一下無(wú)機(jī)械性加載電機(jī)

53、的制動(dòng)操作規(guī)則：</p><p>　　規(guī)則2：轉(zhuǎn)子在制動(dòng)過(guò)程當(dāng)中（從額定轉(zhuǎn)速到零轉(zhuǎn)速）散發(fā)的熱量是原來(lái)所有旋轉(zhuǎn)部分所含動(dòng)能的三倍。</p><p><b>　　3 感應(yīng)電機(jī)的剎車</b></p><p>　　一個(gè)感應(yīng)電機(jī)和它的高慣性負(fù)載同樣可以由定子繞組回路中的電流來(lái)進(jìn)行快速制動(dòng)。任何的兩個(gè)定子端口都可以接在直流電源上。</p>

54、<p>　　直流電流會(huì)在定子上產(chǎn)生恒定的N極和S極，產(chǎn)生的磁極的數(shù)量跟電機(jī)在正常情況下產(chǎn)生的磁極數(shù)相等。因此，一個(gè)三相四極的感應(yīng)電機(jī)不管其端口是如何接在直流電源上的，它都能產(chǎn)生4個(gè)直流磁極。</p><p>　　當(dāng)轉(zhuǎn)子經(jīng)過(guò)這個(gè)恒定磁場(chǎng)時(shí)，在轉(zhuǎn)子鐵片的上會(huì)產(chǎn)生一個(gè)交流電壓。這個(gè)電壓將產(chǎn)生一個(gè)交流電流，這個(gè)電流會(huì)在轉(zhuǎn)子上產(chǎn)生的能量損耗而轉(zhuǎn)移到旋轉(zhuǎn)部分的動(dòng)能中。當(dāng)所有的動(dòng)能都以熱能的形式的耗盡的時(shí)候，電機(jī)就停

55、下來(lái)了。</p><p>　　直流剎車燈的優(yōu)點(diǎn)是它產(chǎn)生的熱量遠(yuǎn)遠(yuǎn)低于上一節(jié)的制動(dòng)方法。這種方法非常有效，因?yàn)樗谵D(zhuǎn)子中所消耗的能量只相等于一開(kāi)始儲(chǔ)存在旋轉(zhuǎn)部分的動(dòng)能，而不是像上節(jié)的制動(dòng)方法那樣是這個(gè)數(shù)字的三倍。這個(gè)能量損耗跟強(qiáng)直流電流是沒(méi)有關(guān)系。然而，用較弱的直流電流來(lái)剎車會(huì)增加剎車時(shí)間。故直流電流可以是額定電流的二到三倍，如果假設(shè)定子尚未變得過(guò)熱，這個(gè)電流甚至可以更高。剎車轉(zhuǎn)矩同比于直流剎車電流的平方。<

56、/p><p><b>　　4 非正常情況</b></p><p>　　電機(jī)的非正常運(yùn)轉(zhuǎn)可能是由于內(nèi)部的原因（定子的短路、軸承過(guò)熱等）或者外部環(huán)境的問(wèn)題引起的。外部問(wèn)題可能由以下原因引起：</p><p><b>　　機(jī)械性過(guò)載</b></p><p><b>　　供電電壓的改變</b&g

57、t;</p><p><b>　　單相失相運(yùn)行</b></p><p><b>　　頻率的變動(dòng)</b></p><p>　　我們將在下一節(jié)探討一下這些問(wèn)題的本質(zhì)。</p><p>　　由國(guó)家標(biāo)準(zhǔn)可知，電機(jī)在電壓浮動(dòng)不超過(guò)正常電壓的＋10％，頻率浮動(dòng)不超過(guò)正常頻率的＋5％是才能正常運(yùn)行。如果電壓頻率同

58、時(shí)變動(dòng)，它們的浮動(dòng)百分比之和絕對(duì)不能超過(guò)10％。最后還要提到的是，所有的電機(jī)都是被設(shè)計(jì)成可在海拔1000米的地方正常工作，那么在高海拔地區(qū)因?yàn)榭諝廨^為稀薄，冷卻力就較為薄弱，所以電機(jī)溫度可能會(huì)超過(guò)允許極限。</p><p><b>　　5 機(jī)械性過(guò)載</b></p><p>　　盡管標(biāo)準(zhǔn)感應(yīng)電機(jī)可以在短時(shí)間內(nèi)產(chǎn)生兩倍于額定的功率，但它們不能一直工作在超過(guò)額定能力的狀態(tài)

59、。過(guò)載會(huì)產(chǎn)生過(guò)熱，導(dǎo)致絕緣部分被破壞，減短了電機(jī)的工作壽命。實(shí)際上，過(guò)載會(huì)引起在電機(jī)箱中的繼電器過(guò)熱，并引起繼電器的斷開(kāi)，最后使電機(jī)在溫度變得過(guò)高之前就停下來(lái)。</p><p>　　某些具有防水功能的電機(jī)被設(shè)計(jì)成可持續(xù)加載超過(guò)15％的過(guò)負(fù)載。這種過(guò)負(fù)載能力可以在銘牌上的保險(xiǎn)系數(shù)上看到。這時(shí)就允許防水電機(jī)的溫度比加載正常電阻時(shí)升高。</p><p>　　在緊急狀況下，一個(gè)防水電機(jī)可以加載12

60、5％的過(guò)負(fù)載，只要在電機(jī)外部安裝了額外的通風(fēng)設(shè)備。但是我們還是不建議長(zhǎng)時(shí)間的過(guò)載，因?yàn)楸M管電機(jī)外殼已經(jīng)被冷卻，但是內(nèi)部繞組的溫度可能已經(jīng)超過(guò)了。</p><p><b>　　6 線電壓的改變</b></p><p>　　由線電壓的改變引起的最大的問(wèn)題是它對(duì)轉(zhuǎn)矩速度特征曲線的影響。在任何速下的轉(zhuǎn)矩實(shí)質(zhì)上總是和應(yīng)用電壓的平方成正比的。因此，如果定子電壓降低了10％，那么任

61、何速度下的轉(zhuǎn)矩都將降低將近20％。由于啟動(dòng)電流比較大，所以線性電壓壓降一般都形成于啟動(dòng)過(guò)程當(dāng)中。故由于低壓的原因，啟動(dòng)轉(zhuǎn)矩一般都比額定值小了很多。</p><p>　　另一方面，如果電機(jī)在運(yùn)行過(guò)程當(dāng)中電壓過(guò)高，各個(gè)磁極上的磁通就會(huì)超過(guò)正常值。由于電機(jī)一直運(yùn)行在全荷負(fù)載，將增加鐵損耗和磁化電流，隨之產(chǎn)生輕微的升溫和功率因素的降低。</p><p>　　如果三相電壓出現(xiàn)了不平衡情況，會(huì)在線電路

62、引起嚴(yán)重的線電流的不平衡。這種情況將增加在定子和轉(zhuǎn)子上的損耗，導(dǎo)致高溫產(chǎn)生。如果一個(gè)電壓不平衡情況盡管只有3.5％，還是會(huì)引起的升溫。當(dāng)電壓之間的相位之差大于2％的時(shí)候，就必須要通知廠家了。</p><p><b>　　7 失相運(yùn)行</b></p><p>　　如果三相線電路中有一路出現(xiàn)了開(kāi)路，或者三相電機(jī)在運(yùn)行時(shí)有一個(gè)熔斷器被斷開(kāi)，電機(jī)會(huì)像單相電機(jī)一樣繼續(xù)運(yùn)行。在剩

63、下的兩條電路中流過(guò)的電流將變成原來(lái)的兩倍，電機(jī)會(huì)由此過(guò)熱。保護(hù)電機(jī)的熱動(dòng)繼電器會(huì)斷開(kāi)電路中的斷路器，從而使電機(jī)從線電路中斷開(kāi)。</p><p>　　當(dāng)電機(jī)在失相運(yùn)行時(shí)，轉(zhuǎn)矩速度特征曲線會(huì)收到嚴(yán)重的影響。制動(dòng)轉(zhuǎn)矩將降低到原來(lái)大小的大約40％，電機(jī)也不會(huì)產(chǎn)生啟動(dòng)轉(zhuǎn)矩。因此一個(gè)全荷負(fù)載的三相電機(jī)如果其中一條線路忽然斷開(kāi)，那么它會(huì)很容易就停下來(lái)。被鎖轉(zhuǎn)子的最終電流是正常的三相LR電路電流的90％，因此它足夠大去關(guān)斷電路的

64、斷路器或者燒掉熔斷器。</p><p>　　圖14.11 三相鼠籠電機(jī)在正常運(yùn)行時(shí)和在單相失相情況下的標(biāo)準(zhǔn)轉(zhuǎn)矩－速度曲線（圖略）</p><p>　　圖14.11表示了一個(gè)三相電機(jī)在正常運(yùn)行和單相失相時(shí)的典型的轉(zhuǎn)矩－速度特征曲線。我們注意到這兩個(gè)特征曲線緊緊地互相跟隨，直到轉(zhuǎn)矩接近單相極限轉(zhuǎn)矩。</p><p><b>　　8 頻率的變動(dòng)</b>

65、;</p><p>　　在大型的分布式系統(tǒng)中除非經(jīng)歷在一個(gè)巨大的干擾，一般從不對(duì)重要的頻率進(jìn)行變動(dòng)，。然而，當(dāng)獨(dú)立系統(tǒng)的電能是由柴油機(jī)或燃?xì)鉁u輪產(chǎn)生時(shí)，它的頻率或許會(huì)進(jìn)行巨變。醫(yī)院的緊急供電設(shè)備，船上的電力系統(tǒng)，伐木場(chǎng)中的發(fā)電機(jī)等都上這種類型的供電設(shè)備。</p><p>　　頻率變動(dòng)導(dǎo)致的最重要的結(jié)果是電機(jī)速度的改變：如果頻率降低了5％，那么電機(jī)的速度也將降低5%。</p>

66、<p>　　從標(biāo)準(zhǔn)頻率是50赫茲的國(guó)家進(jìn)口的機(jī)床和其他電機(jī)驅(qū)動(dòng)的裝置如果接到60赫茲的系統(tǒng)中將會(huì)出現(xiàn)問(wèn)題。所有部件都比正常時(shí)運(yùn)行快了20％，這在一些電器中是不允許的。在這種情況下我們必須給電機(jī)速度降擋，或者提供一個(gè)昂貴的額外的50赫茲的電源。</p><p>　　一個(gè)50赫茲的電機(jī)在60赫茲的線電路中正常運(yùn)行，但是它的端口電壓必須提高到銘牌標(biāo)志的6/5（或者是120％）。新的極限轉(zhuǎn)矩跟原來(lái)的極限轉(zhuǎn)矩是相