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2024年2月29日发(作者:chopsticks怎么拼读)
Electric Motors
Each type of motor has its particular field of usefulness. Because
of its simplicity, economy, and durability, the induction motor is more
widely used for industrial purposes than any other type of ac motor ,
especially if a high-speed drive is desired.
If ac power is available, all drives requiring constant speed should
use squirrel-cage induction or synchronous motors because of their
ruggedness and lower cost. Drives requiring varying speeds, such as fans,
blowers, or pumps, may be driven by wound-rotor induction motors. However,
if there are machine tools or other machines requiring adjustable speed
or a wide range of speed control, it will probably be desirable to install
dc motors on such machines and supply them from the ac system by
motor-generator sets or electronic rectifiers.
Almost all constant-speed machines may be driven by ac squirrel-cage
motors because these motors are made with a variety of speed and torque
characteristics. When large motors are required or when power supply is
limited, the wound-rotor motor is used, even to drive constant-speed
machines.
For varying-speed service, wound-rotor motors with resistance
control are used for fans, blowers, and other apparatus for continuous
duty. The controller and resistors must be properly chosen for the
specific application. Synchronous motors may be used for almost any
constant-speed drive requiring about 100 hp or over.
Cost is an important factor when more than one type of ac motor is
applicable. The squirrel-cage motor is the least expensive ac motor of
the three types considered and requires very little control equipment.
The wound-rotor is more expensive and requires additional secondary
control. The synchronous motor is even more expensive and requires a
source of dc excitation, as well as special synchronizing control to apply
the dc power at the correct instant. When very large large machines are
involved, as, for example, 1000 hp or over, the cost picture may change
considerably and should be checked on an individual basis.
The various types of single-phase ac motors and universal motors are
used very little in industrial applications, since polyphase ac or dc
power is generally available. When such motors are used, they are usually
built into the equipment by the machinery manufacturer, as in portable
tools, office machinery, and other equipment. These motors are, as a rule,
especially designed for the specific machines with which they are used.
电 动 机
每种型号的电机都有其特定的使用范围。与其它型号的交流电机相比,感应电动机因其简单、经济和耐用而更广泛地用于工业,特别是需要高速驱动时更是如此。
因为鼠笼式感应电动机或同步电动机经久耐用且成本低,若有交流电源可用,所有需要恒速驱动的装置应使用这两种电机。需要变速驱动的装置,如电扇、鼓风机或水泵可由线绕式转子感应电动机驱动。然而,对于那些需要调速或速控范围较广的机床或其它机器而言,安装直流电动机,并通过电动机—发电机组或者电子整流器从交流电系统向其提供电能是较为理想的做法。
因为鼠笼式电机具有多种速度和转矩特性,几乎所有的恒速机器均可由交流鼠笼式电动机驱动。当需要大功率电动机或电源受限制时,则可使用线绕式转子电动机,即使是驱动恒速机器。
对于变速作业,由电阻控制的线绕转子电机可用于驱动电风扇、鼓风机和其它装置的持续作业,也可用于起重机、卷扬机等机械和设备的间歇作业。某些特殊应用时,须挑选适当的控制器和电阻器。几乎任何一种需要100马力以上的恒速驱动装置都可使用同步电动机。
当不只一种交流电动机可供挑选使用时,成本便成了很重要的考虑因素。鼠笼式电动机是可供选择的三种型号中价格最低廉的,而且几乎不需要控制装置。绕线式转子电动机昂贵一些,且需要另加次级控制。同步电动机则更贵,而且需要直流励磁电源和专门的同步控制器以便在适当的瞬间接入直流电源。当涉及到1000马力以上的大功率机器时,成本情况会大大改变,需针对各自情况逐个核算。
因为通常有多相交流电源或直流电源可用,因此,在工业上很少使用各种类型的单相交流电动机和交直流两用电动机。如需使用这类电动机,机械制造商常把它们安装在设备中,如便携式工具、办公机械及其它设备。总的来说,这些电动机是为使用它们的专用机器特别设计的。
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