电大《电气传动与调速系统》期末复习试题及参考答案_
电大《电气传动与调速系统》试题 一、选择题（每题 2分，共10分） 1．他励式直流电动机在制动方法中哪种方法的方程式与电动状态时的方程式相同（ A ） A.反馈制动 B.电源反接 C.能耗制动 D.以上都是 2．哪种电动机的机械硬度最大（ C ） A.直流电动机 B.三相异步电动机 C.同步电动机 3．在三相异步电动机的调速方法中，哪种方法最复杂（ D ） A.调压调速 B.转子电路串电阻调速 C.变极调速 D.变频调速 4．三相异步电动机定子旋转磁场的转速与转子的转速之间的相互关系是（ A ） A.定子旋转磁场转速大于转子的转速 B.定子旋转磁场转速等于转子的转速 C.定子旋转磁场转速小于转子的转速 D.定子旋转磁场转速是转子的转速的2倍 二、判断题（每题1分，共计10分） 1.机械效率影响电动机与生产机械之间的速度传动关系。
（ 错误） 2.在正常情况下同步电动机的机械硬度是绝对硬特性的。
（正确 ） 3.直流电动机的调速范围只有在静差率一定的条件下才有意义。
（正确 ） 4.电动机的速度调节与速度变化的含义是相同的。
（ 错误 ） 5.在改变极对数调速中，Y-YY方法具有恒转矩调速性质。
（正确 ） 6．三相异步电动机能耗制动的强弱程度只与所通直流电流大小有关。（错误 ） 7．同步电动机的整个旋转磁场都是由定子电路产生的。
（ 错误） 三、填空题（每空1分，共10分） 1. 在多轴系统中负载转矩和飞轮转矩的折算原则分别是 功率守恒 、 能量守恒 。
2. 限制直流电动机的启动电流，一般有 外串电阻 和 降压 两种方法。
3. 三相交流异步电动机的制动方法有：能耗制动、 反接制动 、 反馈制动 。
4. 一台直流发电机，已知数据如下：PN=180KW，UN=230V，nN=1450rpm，ηN=89.5%， 则该发电机的额定电流为 A，额定转矩为 Nm。
5. 三相异步电动机进行星-三角降压起动时，起动电流为直接起动时的 倍，起动转矩为直接起动时的 倍。
四、简答（每小题5分，共15分） 1. 简述直流电动机不能直接启动的原因。
答：(1).换向器、电机绕组；
（2）.生产机械；
（3）.电网影响。
2.常用速度反馈元件有哪些？其输出与转速的关系？ 答：常用速度反馈元件有：测速发电机、光电编码器。测速发电机一般输出为直流电压，电压幅值与转速呈线性关系。光电编码器输出为频率可变的脉冲，其频率值与转速呈线性关系。 五、计算设计题（55分） 1.一台直流他励电动机的技术数据为：PN=7.5kW，UN=220V，IN=35A,nN=1500r/min，Ra=0.25Ω，计算出此电动机的如下特性： (1)固有机械特性；
(2)电枢附加电阻分别为3Ω和5Ω时的人为机械特性；
(3)电枢电压为UN/2时的人为机械特性；
(4)磁通Φ=0.8ΦN时的人为机械特性。（25分） 解：（1）根据公式：=（220-35×0.25）÷1500=0.141 =9.55×0.141=1.345 根据固有机械特性方程：=220÷0.141-0.25÷（0.141×1.345）T =1560-1.318T （2）电枢附加电阻分别为3Ω和5Ω时的人为机械特性：
=1560-（0.25+3）÷（0.141×1.345）T=1560-31T =1560-（0.25+5）÷（0.141×1.345）T=1560-27.7T (3)电枢电压为UN/2时的人为机械特性：
=1560÷2-1.318T=780-1.318T (4)磁通Φ=0.8ΦN时的人为机械特性：
=1560÷0.8-1.318÷0.64T=1950-2.059T 2．直流他励电动机的数据：PN=55kW，UN=220V，IN=280A,nN=635r/min，Ra=0.044Ω，带额定负载转矩运行，求： (1)如果要求静差率S≤20%，采用电枢回路串电阻调速和降压调速时所能达到的调速范围；
(2)如果要求调速范围D=4,采用以上两种调速方法时的最大静差率。
（15分） 解：（1）求调速范围： ①电枢回路串电阻调速时， ≤20% 额定负载转矩时容许的转速降为 =20% =0.2×672.8=134.6r/min 容许的最低转速为 nmin=n0- =672.8-134.6=538.2r/min，则调速范围为 ②降压调速时，(额定负载转矩下的转速降 =37.8r/min)容许的最低理想空载转速为 容许的最低转速为 则调速范围为 (2)调速范围D=4时的最大静差率： ①电枢回路串电阻调速时，容许的最低转速为 最低转速时的转速降为 则最大静差率为 ②降压调速时，容许的最低转速为 最低转速时的理想空载转速为 则最大静差率为 3.一直流他励电动机，其额定功率PN=40kW，额定电压UN=220V，额定电流IN=203.3A，额定转速nN=1500r/min，电枢绕组电阻Ra=0.06Ω，系统的飞轮惯量GD2=15N·m2，负载转矩TL是额定电磁转矩TN的0.6倍。若在电动机额定电流的二倍的条件下启动，试求：
(1)应串入电枢回路的电阻Rad；
(2)启动过程中的Ia(t)、n(t)；
(3)启动时间。
（15分） 解：（1） 启动瞬间电枢回路总电阻为 (2)启动过渡过程的时间常数为 电流初值为 Ist=2IN=2×203.3=406.6A 额定电磁转矩为 负载转矩为 TL=0.6TN=0.6×270=162N·m 电枢稳态电流为 理想空载转速为 设最终稳态转速为ns，则由 得 于是可得 (3)启动所需时间取4 ，则 请您删除一下内容，O(∩_∩)O谢谢！！！2015年中央电大期末复习考试小抄大全，电大期末考试必备小抄，电大考试必过小抄After earning his spurs in the kitchens of The Westin, The Sheraton, Sens on the Bund, and a sprinkling of other top-notch venues, Simpson Lu fi nally got the chance to become his own boss in November 2010. Sort of. The Shanghai-born chef might not actually own California Pizza Kitchen (CPK) but he is in sole charge of both kitchen and frontof- house at this Sinan Mansions＇stalwart. “It’s certainly a responsibility to be the head chef, and then to have to manage the rest of the restaurant as well,“ the 31-year-old tells Enjoy Shanghai. “In hotels, for example, these jobs are strictly demarcated, so it’s a great opportunity to learn how a business operates across the board.“ It was a task that management back in sunny California evidently felt he was ready for, and a vote of confi dence from a company that, to date, has opened 250 outlets in 11 countries. And for added pressure, the Shanghai branch was also CPK’s China debut. “For sure it was a big step, and unlike all their other Asia operations that are franchises, they decided to manage it directly to begin with,“ says Simpson. Two years ago a private franchisee took over the lease, but the links to CPK headquarters are still strong, with a mainland-based ＇brand ambassador’ on hand to ensure the business adheres to its ethos of creating “innovative, hearth-baked pizzas“, a slice of PR blurb that Simpson insists lives up to the hype. “They are very innovative,“ he says. “The problem with most fast food places is that they use the same sauce on every pizza and just change the toppings. Every one of our 16 pizza sauces is a unique recipe that has been formulated to complement the toppings perfectly.“ The largely local customer base evidently agrees and on Saturday and Sunday, at least, the place is teeming. The kids-eat-for-free policy at weekends is undoubtedly a big draw, as well as is the spacious second-fl oor layout overlooked by a canopy of green from Fuxing Park over the road. The company is also focusing on increasing brand recognition and in recent years has taken part in outside events such as the regular California Week. Still, the sta are honest enough to admit that business could be better; as good, in fact, as in CPK’s second outlet in the popular Kerry Parkside shopping mall in Pudong. “Sinan Mansions has really struggled to get the number of visitors that were envisaged when it first opened, and it hasn’t been easy for any of the tenants here,“ adds Simpson. “We’re planning a third outlet in the city in 2015, and we will probably choose a shopping mall again because of the better foot traffic.“ The tearooms once frequented by Coco Chanel and Marcel Proust are upping sticks and coming to Shanghai, Xu Junqian visits the Parisian outpost with sweet treats. One thing the century-old Parisian tearoom Angelina has shown is that legendary fashion designer Coco Chanel not only had style and glamor but also boasted great taste in food, pastries in particular. One of the most popular tearooms in Paris, Angelina is famous for having once been frequented by celebrities such as Chanel and writer Marcel Proust. Now Angelina has packed up its French ambience, efficient service, and beautiful, comforting desserts and flown them to Shanghai. At the flagship dine-in and take-out space in Shanghai, everything mimics the original tearoom designed from the beginning of the 20th century, in Paris, the height of “Belle Epoque“. The paintings on the wall, for example, are exactly the same as the one that depicts the landscape of southern France, the hometown of the owner; and the small tables are intentional imitations of the ones that Coco Chanel once sat at every afternoon for hot chocolate. The famous hot chocolate, known as L’Africain, is a luxurious mixture of four types of cocoa beans imported from Africa, blended in Paris and then shipped to Shanghai. It’s sinfully sweet, rich and thick as if putting a bar of melting chocolate directly on the tongue and the fresh whipped cream on the side makes a light, but equally gratifying contrast. It is also sold in glass bottles as takeaway. The signature Mont-Blanc chestnut cake consists of three parts: the pureed chestnut on top, the vanilla cream like stuffing, and the meringue as base. Get all three layers in one scoop, not only for the different textures but also various flavors of sweetness. The dessert has maintained its popularity for a century, even in a country like France, perhaps the world’s most competitive place for desserts. A much overlooked pairing, is the Paris-New York choux pastry and N226 chocolate flavored tea. The choux pastry is a mouthful of airy pecan-flavored whipped cream, while the tea, a blend of black teas from China and Ceylon, cocoa and rose petals, offers a more subtle fragrance of flowers and chocolate. Ordering these two items, featuring a muted sweetness, makes it easier for you to fit into your little black dress. Breakfast, brunch, lunch and light supper are also served at the tearoom, “a hub of many cultures“ and takes in “a mix of different styles of French cuisines“, according to the management team. The semi-cooked foie gras terrine, is seductive and deceptive. It’s generously served at the size and shape of a toast, while the actual brioche toast is baked into a curved slice dipped with fig chutney. The flavor, however, is honest: strong, smooth and sublime. And you don’t actually need the toast for crunchiness. This is the season for high teas, with dainty cups of fine china and little pastries that appeal to both visual and physical appetites. But there is one high tea with a difference, and Pauline D. Loh finds out just exactly why it is special. Earl Grey tea and macarons are all very well for the crucial recuperative break in-between intensive bouts of holiday season shopping. And for those who prefer savory to sweet, there is still the selection of classic Chinese snacks called dim sum to satisfy and satiate. High tea is a meal to eat with eye and mouth, an in-between indulgence that should be light enough not to spoil dinner, but sufficiently robust to take the edge off the hunger that strikes hours after lunch. The afternoon tea special at Shang-Xi at the Four Seasons Hotel Pudong has just the right elements. It is a pampering meal, with touches of luxury that make the high tea session a treat in itself. Whole baby abalones are braised and then topped on a shortcrust pastry shell, a sort of Chinese version of the Western vol-au-vent, but classier. Even classier is the dim sum staple shrimp dumpling or hargow, upgraded with the addition of slivers of midnight dark truffles. This is a master touch, and chef Simon Choi, who presides unchallenged at Shang-Xi, has scored a winner again. Sweet prawns and aromatic truffles — what’s not to love? His masterful craftsmanship is exhibited in yet another pastry — a sweet pastry that is shaped to look like a walnut, but which you can put straight into the mouth. It crumbles immediately, and the slightly sweet, nutty morsel is so easy to eat you’ll probably reach straight for another. My favorite is the dessert that goes by the name yangzhi ganlu, or ambrosia from the gods. The hotel calls it chilled mango cream with sago, pomelo and bird’s nest – made with ingredients that resonate with every female soul. It does taste like ambrosia, with the sweet-sour fragrance of the mango forming the first layer of taste and sensation, and the pomelo sacs and sago pearls providing the tactile contrast. The bird’s nest — it’s the ingredient that gilds the lily, since it is supposed to nourish and nurture a perfect complexion. For those unfamiliar with this exotic ingredient, the bird’s nest is not a bundle of twigs, but is, instead, the dried secretion that cave swifts use to build their nest. Technically, it’s bird saliva, but the Chinese believe that it has collagen-boosting properties essential to beauty. To me, it just tastes good, adding a slight gelatinous crunch to the back of the teeth. There is also a baked mushroom puff pastry that includes the highly prized Matsutake or pine mushroom. You also get a choice of teas, but I strongly recommend the aged Pu’er from Yunnan province. It is a mellow tea that will go perfectly with the rich little nuggets, and will warm you up on a cold afternoon. Incidentally, the general guide is green tea such as Longjing or Dragonwell for the hot season, semi-fermented teas like Wu-long or Iron Buddha for autumn, and more warming teas like Pu’er for winter. The Shang-Xi afternoon tea costs 228 yuan ($37) per person, and 388 yuan for the more opule