| Popis: |
For the most part, since the advent of talking pictures, motors have been employed whose performance is excellent. The various types of motor, however, differ widely in their ability to resist load irregularities and in their tendency to oscillate when a disturbance occurs. For the more critical applications these factors deserve careful consideration when the type or design is being selected. The principal types of synchronous motor are (1) the variable-reluctance or induced-pole motor, (2) the separately excited motor, (3) the a-c-d-c motor, (4) the hysteresis motor, (5) the low-speed multi-tooth motor (of the type used for electric clocks), (6) the poly-phase, uniform-torque modification of number 5, and (7) selsyn motors. — Many of the characteristics of synchronous motors may best be understood by assuming that the poly-phase winding produces a uniformly rotating magnetic field, but estimating the stiffness and stability demands a knowledge of the manner in which the a-c input varies with mechanical displacement. Generous pole-face grids are essential for stability. A-c-d-c motors have certain elements of instability as well as stabilizing factors, which are not present in straight synchronous motors. The magnitude of these effects can to some extent be controlled by the external circuit arrangements. Selsyn motors are less readily damped than regular synchronous motors, and for this reason arrangements by which the synchronous motors can be interlocked from standstill are of interest. |
