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1、專業(yè)好文檔機電控制與可編程序控制器技術(shù)課程習(xí)題分析與詳解（一）1隔離開關(guān)和負荷開關(guān)配合使用時，對它們的操作順序有什么規(guī)定？答：分閘：應(yīng)先斷開負荷開關(guān)，再斷開隔離開關(guān)。合閘：應(yīng)先合上隔離開關(guān)，后合上負荷開關(guān)。2組合開關(guān)的結(jié)構(gòu)有什么特點？型號的含義是什么？答：組合開關(guān)由動觸片、靜觸片、方形轉(zhuǎn)軸、手柄、定位機構(gòu)和外殼等部分組成。它的動、靜觸片分別疊裝在數(shù)層絕緣墊板內(nèi)組成雙斷點橋式結(jié)構(gòu)。而動觸片又套裝在有手柄的絕緣方軸上，方軸隨手柄而旋轉(zhuǎn)。于是每層動觸片隨方軸轉(zhuǎn)動而變化位置來與靜觸片分斷和接觸。組合開關(guān)的頂蓋部分由凸輪、彈簧及手柄等零件構(gòu)成操作機構(gòu)，這個機構(gòu)由于采用了彈簧儲能，使開關(guān)快速閉合及分斷。組

2、合開關(guān)的分合速度與手柄的旋轉(zhuǎn)速度無關(guān)，有利于滅弧。組合開關(guān)型號的含義如下圖所示觸刀極數(shù)每極觸刀額定電流（A）設(shè)計序號組合式刀開關(guān)組合開關(guān)型號的意義 H Z /- 3接觸器的用途是什么？選擇接觸器時主要考慮那些技術(shù)數(shù)據(jù)？答：接觸器用來頻繁地接通和切斷主電路或大容量控制電路，它廣泛地用于控制電動機和其它電力負載。選擇接觸器主要考慮以下技術(shù)數(shù)據(jù)： 電源種類：交流或直流。 主觸點額定電壓、額定電流。 輔助觸點種類、數(shù)量及觸點額定電流。 勵磁線圈的電源種類、頻率和額定電壓。 額定操作頻率（次/h），即允許的每小時接通的最多次數(shù)。4比較接近式行程開關(guān)與機械式行程開關(guān)的優(yōu)缺點。答：接近式行程開關(guān)具有定位精度

3、高、操作頻率高、功率損耗小、壽命長、耐沖擊振動、耐潮濕、能適應(yīng)惡劣工作環(huán)境等優(yōu)點。5比較交、直流電磁鐵的特點。答：交流電磁鐵的特點：勵磁電流與銜鐵位置有關(guān)，當銜鐵處于起動位置時，電流最大；當銜鐵吸合后，電流就降到額定值。吸力與銜鐵位置有關(guān)，但影響比直流電磁鐵小的多，隨著氣隙的減小，其吸力將逐漸增大，最后將達到1.52倍的初始吸力。直流電磁鐵的特點：勵磁電流的大小僅取決于勵磁線圈兩端的電壓及本身的電阻，而與銜鐵的位置無關(guān)。直流電磁鐵的吸力在銜鐵起動時最小，而在吸合時最大，6一臺三相異步電動機，額定功率為5.5KW，額定電壓為380V，額定電流為11.25A，起動電流為額定電流的7倍，試選用對它進

4、行控制和保護用的按鈕、接觸器、熱繼電器和組合開關(guān)。解：電動機的額定電流，起動電流為控制電路采用交流220V供電。則起動按鈕（優(yōu)先選綠色）和停止按鈕（優(yōu)先選紅色）選用額定電壓220V的即可。接觸器選用交流接觸器，主觸點的額定電壓380V，額定電流應(yīng)78.75V，勵磁線圈選擇額定電壓交流220V，頻率50Hz。熱繼電器的額定電流應(yīng)1.05IN=1.05×11.25=11.8A。組合開關(guān)的額定電壓為交流380V，三極觸點，額定電流78.25A即可。7在下表中填上電器的圖形符號和文字符號。名稱文字符號圖形符號線圈（元件）常開觸點常閉觸點刀開關(guān)Q接觸器KM時間繼電器延時閉合ST延時斷開延時閉合

5、和延時斷開空氣斷路器QF按鈕SB速度繼電器KS熱繼電器FR熔斷器FU行程開關(guān)ST8.自鎖環(huán)節(jié)怎樣組成？它起什么作用？并具有什么功能？答：一般可用起動按鈕和接觸器的常開觸點并聯(lián)，然后再和接觸器的線圈串聯(lián)可得。當按下起動按鈕后，可實現(xiàn)長動，它又具有失壓保護功能。9什么是互鎖環(huán)節(jié)，它起到什么作用？答：將兩個接觸器的常閉觸點分別串聯(lián)到對方的線圈回路中，即可得到互鎖。它用來防止兩個接觸器同時得電。10 試設(shè)計一臺異步電動機的控制線路。要求：（1）能實現(xiàn)起、停的兩地控制；（2）能實現(xiàn)點動調(diào)整；（3）能實現(xiàn)單方向的行程保護；（4）要有短路和過載保護。SB5KMKSB1KSB3SB2KSB4STFRM3QKM

6、FRu v wFU1FU2圖1解：如圖1所示，左側(cè)為主電路，右側(cè)為控制電路。SB1 和SB2 是長動起動按鈕，SB3 和SB4是停止按鈕，SB5是點動按鈕，行程開關(guān)ST的常閉觸點起行程保護作用，熔斷器起短路保護作用，熱繼電器起過載保護作用。11今有兩臺電動機，每次只允許一臺運轉(zhuǎn)且一臺只需單方向運轉(zhuǎn)，另一臺要求能正反轉(zhuǎn)。兩臺電動機都要求有短路保護和過載保護，試畫出其電路。KM2M13M23KM3FR1FR2KM1Qu v wFU1FU2SB2KM3KM1KM3SB1KM2KM2SB4KM2KM1KM1KM2SB3KM3KM3KM1FR1FR2圖2解：如圖2所示。電動機M2可單向運行，KM3為其控

7、制接觸器；電動機M3可正反轉(zhuǎn)運行，KM1和KM2分別為正、反轉(zhuǎn)接觸器。"If we don't do that it will go on and go on. We have to stop it; we need the courage to do it."His comments came hours after Fifa vice-president Jeffrey Webb - also in London for the FA's celebrations - said he wanted to meet Ivory Coast internat

8、ional Toure to discuss his complaint.CSKA general director Roman Babaev says the matter has been "exaggerated" by the Ivorian and the British media.Blatter, 77, said: "It has been decided by the Fifa congress that it is a nonsense for racism to be dealt with with fines. You can always

9、 find money from somebody to pay them."It is a nonsense to have matches played without spectators because it is against the spirit of football and against the visiting team. It is all nonsense."We can do something better to fight racism and discrimination."This is one of the villains

10、we have today in our game. But it is only with harsh sanctions that racism and discrimination can be washed out of football."The (lack of) air up there Watch mCayman Islands-based Webb, the head of Fifa's anti-racism taskforce, is in London for the Football Association's 150th anniversa

11、ry celebrations and will attend City's Premier League match at Chelsea on Sunday."I am going to be at the match tomorrow and I have asked to meet Yaya Toure," he told BBC Sport."For me it's about how he felt and I would like to speak to him first to find out what his experienc

12、e was."Uefa has opened disciplinary proceedings against CSKA for the "racist behaviour of their fans" during City's 2-1 win.Michel Platini, president of European football's governing body, has also ordered an immediate investigation into the referee's action

13、s.CSKA said they were "surprised and disappointed" by Toure's complaint. In a statement the Russian side added: "We found no racist insults from fans of CSKA."Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunda.The weather

14、 plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our da

15、y-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause),e can expect

16、 a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet ( Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Sti

17、ll, he'll be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds

18、. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes it

19、9;s not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it won't. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).cause there