Motors intermittent duty

The nonoriented steels are subdivided into low, intermediate, and high siUcon steels. The first contain about 0.5—1.5% siUcon, used mainly in rotors and stators of motors and generators. Steels containing ca 1% siUcon are used for reactors, relays, and small intermittent-duty transformers. 

Intermediate siUcon steels (2.5—3.5% Si) are used in motors and generators of average to high efficiency and in small- to medium-size intermittent-duty transformers, reactors, and motors. 

I. A CMR motor therefore can be operated at higher outputs on short-time duties as shown in curve (d). The extent to which a CMR motor cun be over-rated to perform a particular short-time or intermittent duty is considered in the follow ing example. While evaluating the rating for such duties, the heat during start-up and during braking and their frequency of occurrence should be considered. 

Figure 12.31 Heating and cooling curves of an intermittent duty motor...

ManuEictuFen of motors classify them accoidii to the amount of time the motor needs to be operated. The motors are generally classified as continuous duty or intermittent duty. The continuous du motors are used in applications where the motor is ejqpected to operate over a period of an hour or longer. In some applications, continuous operation of the motor may be requited. In applications where the motor is expected to operate fi>r short periods of time and then rest, the intermittent duty motors are fiiund. The continuous duty motors are mote expensive than the intermittent duty motors. 

It should be emphasized that special duty cycles for motors, e.g. arduous starting conditions with high moments of inertia or intermittent operation with short duty cycles, restrict the field of application for e -motors (or generally exclude e -motors). 

When using a driver for the first time or intermittently, a motor carrier must obtain from the driver a signed statement giving the total on-duty time dming the preceding 7 days, and the time the driver was last relieved from duty prior to beginning work for the motor carrier. 

The motor carrier that employs the driver maintains for 6 months accurate records showing the time the driver reports for duty each day, the total number of hours the driver is on duty each day, and the time the driver is released from duty each day (and the total time for the preceding 7 days for drivers used for the first time or intermittently, per 395.8(j)(2)). 

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