G电动机的选择 4教学目松 tThe choice of motor 4电动机的发热与温升 4动机的额定功减 4电动机的额定功率的选择 必有风大孚
⑦电动机的选择 教学目标 了解电动机容量选择的基本理论 掌握电力拖动系统中电动机容量选择的工程方 法 必有风大孚
The choice of motor There are many factors which must be considered when choosing a motor for a particular drive. In the following notes, the main points are highlighted but the final choice is usually a matter for the specialist. Not all the factors can be dealt with here, but the summary notes, together with the relevant sections of the main text, will be sufficient to give a good appreciation ofthe general problem. 有风族大学
The solution of this problem is not usually unique and opinions may differ widely in some cases as to he most suitable motor-drive systel However, it may be said in brief that the correct motor is the one which meets the required specification at minimum cost, but this is not a simple matter to estimate. It must include not only the capital cost of the motor-drive system itself but also the running costs. The capital cost includes the provision ofany special supplies find control gear to run the motor 有风族大学
The running cost includes interest, charges on capital equipment and buildings and charges for the power losses consumed in the machine and control circuits; obviously power factor and efficiency are of significance here. Maintenance is also a regular running cost and would normally be higher with complex control gear and with machines having rubbing contacts at slip rings and commentators Installation costs too may be decisive; for example, special foundations are required for motor-generator sets but not for static conversion equipment Such equipment also makes less demands on space and is less noisy than rotating machinery On the other hand, there is considerable harmonic generation which poses a suppression problem 必有风大孚
Some motors are excluded from a particular application because the operating environment is hostile"in some way, as in conditions ofhigh temperature, high vacuum, high speed or in the presence of corrosive liquids, A brushless type of machine then becomes essential. nduction motors are generally the cheapest type off machine especially if a single, cage rotor is satisfactory. The price increases as more demands are made on the control side and which might necessitate a wound-rotor machine 必有风大孚
Even then the power factor remains poor unless correction is applied, and the brushless synchronous machine may therefore become competitive. f simple, infinitely-variable speed- control is required, then a c or d. commutator machines are called for, unless a variable- frequency supply with induction or synchronous motors can be justified. This special supply could be partly ofset against the cost of d.c. or variable-voltage a.c. apparatus required for commutator machines 有风族大学
电动机的选择 电动机的一般选择 a电动机种类〔机种)的选择 主要种类:电力系统中拖动生产机械运行的原动机即驱动电机,包括直流 电动机和交流电动机两种。交流电动机又有异步电动机和同步电动机两 种 种类选择时考虑的主要内容 电动机的机械特性:生产机械具有不同的转矩转速关系,要求电动机的机 械特性与之相适应。 电动机的调速性能:调速范围、调速的平滑性、调速系统的经济性都应该 满足生产机械的要求。 电动机的起动性能 综合观点:以上各方面在旋转电动机时 电源 必须都考虑到,都得到满足后才能选 定;能同时满足以上条件的电动机可能 经济性 不是一种,还应综合其他情况,诸如节 能、货源等加以确定。 有风族大学
电动机的选择 电动机的一般选择 a电动机类型的选择 安装方式:卧式、立式 轴仲个数:仲出到端盖外面与负载联接的转轴部分,称为轴伸。分为单轴 伸和双轴伸。 防护方式:开启式、防护式、封闭式和防爆式几种。 开启式电动机,在定于两侧与端盖上都有很大的通风口。散热好,价格便宜,但 容易进灰尘、水滴、铁屑等杂物。只能在清洁、千燥的环境中使用。 肪护式电动杋,在机座下面有通风口。散热好,能防止水滴、铁屑等从上方落入 电机,但不能防止湖气和灰尘侵入。适用于比较干燥、没有腐蚀性和爆炸性其他的 环境。 封闭式电动机,机座和端盖上均无通风孔,完全是封闭的。又分为自冷式、自扇 冷式、他扇冷式、管道通分式及密封式。 肪爆式电动杋适用干有易燃、易爆气体的场所,如矿井、油库、煤气站等。 有风族大学
电动机的选择 电动机的一般选择 a电动机额定电压和额定转速的选择 额定电压的选择:电动机等级、相数、频率都要与供电电压一致 额定转速的选择:对电动机本身而言,额定功率相岡的电动机额定转速 越高,体积越小,造价越低,一般说电动机转子越细长,转动惯量越 小,斜动时间短。 当生产机械所需额定转速一定的前提下,一般来讲若还需要传动机构减 速,則电动机额定转速越高,传动机构速比越大,机构越复杂,而且传 动损耗也越大。通常电动机额定转速不低于500r/min 不需要调速的高、中速杋楲:如泵、鼓风机、压缩机可选相应额定转速的电 机,而不需要减速机构; 不需调速的低速机械:如球磨杋、破碎杋、某些化工杋械等可选用相应转速的 电动机或有较小速比的减速机构。 调速要求不高的各种生产机床,则可选择转速稍高的电动机配以减速机构或选 多级电动机。 调速要求较高的生产机楲应考虑生产机械最高转速与电动机最高转速相适应, 直接用电气调速。 瓦孩大孚