电大《机电控制与可编程序控制器技术》形成性考核册答案(一)

1、专业好文档机电控制与可编程序控制器技术课程习题分析与详解（一）1隔离开关和负荷开关配合使用时，对它们的操作顺序有什么规定？答：分闸：应先断开负荷开关，再断开隔离开关。合闸：应先合上隔离开关，后合上负荷开关。2组合开关的结构有什么特点？型号的含义是什么？答：组合开关由动触片、静触片、方形转轴、手柄、定位机构和外壳等部分组成。它的动、静触片分别叠装在数层绝缘垫板内组成双断点桥式结构。而动触片又套装在有手柄的绝缘方轴上，方轴随手柄而旋转。于是每层动触片随方轴转动而变化位置来与静触片分断和接触。组合开关的顶盖部分由凸轮、弹簧及手柄等零件构成操作机构，这个机构由于采用了弹簧储能，使开关快速闭合及分断。组

2、合开关的分合速度与手柄的旋转速度无关，有利于灭弧。组合开关型号的含义如下图所示触刀极数每极触刀额定电流（a）设计序号组合式刀开关组合开关型号的意义 h z /- 3接触器的用途是什么？选择接触器时主要考虑那些技术数据？答：接触器用来频繁地接通和切断主电路或大容量控制电路，它广泛地用于控制电动机和其它电力负载。选择接触器主要考虑以下技术数据： 电源种类：交流或直流。 主触点额定电压、额定电流。 辅助触点种类、数量及触点额定电流。 励磁线圈的电源种类、频率和额定电压。 额定操作频率（次/h），即允许的每小时接通的最多次数。4比较接近式行程开关与机械式行程开关的优缺点。答：接近式行程开关具有定位精度

3、高、操作频率高、功率损耗小、寿命长、耐冲击振动、耐潮湿、能适应恶劣工作环境等优点。5比较交、直流电磁铁的特点。答：交流电磁铁的特点：励磁电流与衔铁位置有关，当衔铁处于起动位置时，电流最大；当衔铁吸合后，电流就降到额定值。吸力与衔铁位置有关，但影响比直流电磁铁小的多，随着气隙的减小，其吸力将逐渐增大，最后将达到1.52倍的初始吸力。直流电磁铁的特点：励磁电流的大小仅取决于励磁线圈两端的电压及本身的电阻，而与衔铁的位置无关。直流电磁铁的吸力在衔铁起动时最小，而在吸合时最大，6一台三相异步电动机，额定功率为5.5kw，额定电压为380v，额定电流为11.25a，起动电流为额定电流的7倍，试选用对它进

4、行控制和保护用的按钮、接触器、热继电器和组合开关。解：电动机的额定电流，起动电流为控制电路采用交流220v供电。则起动按钮（优先选绿色）和停止按钮（优先选红色）选用额定电压220v的即可。接触器选用交流接触器，主触点的额定电压380v，额定电流应78.75v，励磁线圈选择额定电压交流220v，频率50hz。热继电器的额定电流应1.05in=1.0511.25=11.8a。组合开关的额定电压为交流380v，三极触点，额定电流78.25a即可。7在下表中填上电器的图形符号和文字符号。名称文字符号图形符号线圈（元件）常开触点常闭触点刀开关q接触器km时间继电器延时闭合st延时断开延时闭合和延时断开空

5、气断路器qf按钮sb速度继电器ks热继电器fr熔断器fu行程开关st8.自锁环节怎样组成？它起什么作用？并具有什么功能？答：一般可用起动按钮和接触器的常开触点并联，然后再和接触器的线圈串联可得。当按下起动按钮后，可实现长动，它又具有失压保护功能。9什么是互锁环节，它起到什么作用？答：将两个接触器的常闭触点分别串联到对方的线圈回路中，即可得到互锁。它用来防止两个接触器同时得电。10 试设计一台异步电动机的控制线路。要求：（1）能实现起、停的两地控制；（2）能实现点动调整；（3）能实现单方向的行程保护；（4）要有短路和过载保护。sb5kmksb1ksb3sb2ksb4stfrm3qkmfru v

6、wfu1fu2图1解：如图1所示，左侧为主电路，右侧为控制电路。sb1 和sb2 是长动起动按钮，sb3 和sb4是停止按钮，sb5是点动按钮，行程开关st的常闭触点起行程保护作用，熔断器起短路保护作用，热继电器起过载保护作用。11今有两台电动机，每次只允许一台运转且一台只需单方向运转，另一台要求能正反转。两台电动机都要求有短路保护和过载保护，试画出其电路。km2m13m23km3fr1fr2km1qu v wfu1fu2sb2km3km1km3sb1km2km2sb4km2km1km1km2sb3km3km3km1fr1fr2图2解：如图2所示。电动机m2可单向运行，km3为其控制接触器；电

7、动机m3可正反转运行，km1和km2分别为正、反转接触器。if we dont 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 fas celebrations - said he wanted to meet ivory coast international toure to discuss his c

8、omplaint.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 find money from somebody to pay them.it is a

9、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 we have today in our game. but it is only with harsh sanctions t

10、hat racism and discrimination can be washed out of football.the (lack of) air up there watch mcayman islands-based webb, the head of fifas anti-racism taskforce, is in london for the football associations 150th anniversary celebrations and will attend citys premier league match at chelsea on sunday.

11、i am going to be at the match tomorrow and i have asked to meet yaya toure, he told bbc sport.for me its about how he felt and i would like to speak to him first to find out what his experience was.uefa hasopened disciplinary proceedings against cskafor the racist behaviour of their fans duringcitys

12、 2-1 win.michel platini, president of european footballs governing body, has also ordered an immediate investigation into the referees actions.cska said they were surprised and disappointed by toures complaint. in a statement the russian side added: we found no racist insults from fans of cska.baumg

13、artner the disappointing news: mission aborted.the supersonic descent could happen as early as sunda.the weather 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 ba

14、lloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-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

15、.17 kilometers) and into the stratosphere. as he crosses the boundary layer (called the tropopause),e can expect 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

16、.below, the earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. still, hell 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 ju

17、mpwhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. 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 o

18、ut of control, he has a stabilization parachute that can be deployed to slow him down. his team hopes its 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 th