However, more efficient and cost effective approach is to select the motor with optimum rating on the basis of the load duration curve for the particular application. Many continuous duty motors even operate under varying load conditions due to chemical process requirements.Īs a common practice, where such variable loads are to be operated, a motor rating is selected based on the highest anticipated load. The crane duty motors are always supposed to operate under varying load conditions and sequential switching due to requirement of handling materials of varied weights (i.e.
The squirrel cage motors are started with direct-on-line starters in most of the cranes. Ø Max = Maximum temperature attained during Duty Cycle N = Duration of motor operation under ratedconditions S5 – Intermittent Periodic Duty with starting and breaking S5 – Intermittent Periodic Duty with starting and breaking Ø Max = Maximum temperature attained during Duty cycle S4 – Intermittent Periodic Duty with starting S4 - Intermittent Periodic Duty with starting The recommended values for CDF are 25, 40 and 60 percent. Unless otherwise specified, the duration of the duty cycle is 10 minutes. Ø Max = Maximum temperature attained during Duty cycle
R = Duration of motor at rest and de-energised N = Duration of motor operation under rated conditions Derivation Of Cyclic Duration Factor From Different Duty Cycles S3 – Intermittent Periodic Duty S3 - Intermittent Periodic Duty