The hoist motor is usually a 30-min or 60-min rated motor, based on
the full-load-up running condition, the worst case. This type of motor
rating is quite useful for the intermittent duty [per Sec.
620-61(b)(1)] required of elevators, where a normal duty cycle might
involve a 40% run time with 120-80 starts per hour under various
conditions of loading. The duty cycle limits the amount of heating,
which removes the necessity for running overload protection (Sec.
430-33) and cuts the required conductor ampacity to the actual hoist
motor (not the AC drive motor) to 90% of nameplate [Table 430-22(a),
Exception].
The resulting hp rating of the drive motor, which is partly a
consequence of its time rating, may therefore vary significantly from
the AC drive motor. This is because, in contrast, the AC drive motor
on Ward Leonard elevator drive systems must be continuously rated in
accordance with the applicable NEMA standard. In addition, the DC
generator may be nominally overloaded as well. Remember, these
generators are usually designed to commutate up to three times their
rated current without excessive arcing at their commutators.
Therefore, you might see 15-hp continuous-rated AC drive motors (with
15-hp controllers) for these elevators with larger hp time-rated hoist
motors. However, if as in this question, the AC drive carries the same
rating as the actual hoist motor, then that rating must be respected
in sizing its controller.
所以，直流电梯的交流电动机功率为连续功率，直流电梯计算功率=交流电动机功率*1.4。
