Crane motors

Generally same as the crane motors, but eompartitively silent in running and have a very low vibration level. For general requirements of other types of lifting and hoisting applications see Table 7.1. 

Table 7.1 Electrical requirements for lift and crane motors...

Textile motors Crane motors Determining the size of motor Sugar centrifuge motors Motors for deep-well pumps Motors for agricultural application Surface-cooled motors Torque motors or actuator motors Vibration and noise level Service factors Motors for hazardous locations Specification of motors for Zone 0 locations Specification of motors for Zone I locations Motors for Zone 2 locations Motors for mines, collieries and quarries Intrinsically safe circuits, type Ex. f Testing and certifying authorities Additional requirements for ciritical installations Motors for thermal power station auxiliaries Selection of a special-purpose motor... 

Whether arty inflanunable or explosive materials are being handled or will be present in the viciiuty of the EOT crane motors should be flameproof in this case)... 

Wound-rotor crane motors with double shaft extension. 

FIG. 10-39 Canned -motor pump CouHesif of Chempump Division, Crane Co.)... 

Saturable reactors, which are adjustable by a small dc signal, have also been used for both primary (stator) and secondary (rotor) control. In the primary they control motor voltage and therefore torque. In combination with fixed secondary resistors and feedback from a tachometer, this system can be used for precise speed and torque control of cranes, hoists, etc. Even reversing can be accomplished by using two saturable reactors in each of two (of three) phases. Other combinations of fixed or saturable reac tors in the primaiy and/or secondaiy, all combined with secondary resistors, provide a wide range of capabiUties and flexibihty for the wound-rotor motor. 

Thyristors have been replacing saturable reactors they are small, efficient, and easily controlled by a wide variety of control systems. A modern crane control drive uses fixed secondary resistors and two sets of primaiy thyristors (one set for hoist, one for lower). With tachometer feedback for speed sensing, the control for the motor provides speed regulation and torque hmiting in both directions, all with static-devices. A wide variety of control systems is possible the control should be designed for the specific application. 

Specific applications for such motors are rolling mills, rice mills, paper mills and cranes etc. for one or more of the following reasons ... 

The mechanical output of the motor for crimes iind hoists in lifting the hook load is the useful work done by it. The losses produced in the crane or hoist mechanism are taken into account by the mechanical efficiency of the hoisting mechanism. 

Duty types. S, S, and. S5 as discussed in Chapter 3 are normally applicable to crane and hoist motors. For duty types S4 and 5. the duty cycle per unit time is greater than S, . The most important factor is the number of switching operations per hour. A temperature rise in the motor occurs during acceleration, braking and reversing. 

Many crane manufacturers specify that the motor should be suitable for half an hour or one hour duration according to the British practice still followed in some countries. In fact, it is not possible to correlate precisely these ratings with any of the duty factors. Hence the motors are designed for any of the duty factors of 15%, 25%, 40% and 60%. In fact the duty factors for different types of cranes have been standardized, depending upon their operation, after several years of experience. For example, the cranes operated in steel industries have different types of duty factors as follows ... 

Manufacturers Association (lEEMA) has issued a standard on crane duty motors in which an attempt is made to list the outputs against the lEC frames for. S, -6. S -150 and 5 s-300 starts/hour duty types. 

Applications include electric motor drives for conveyors and other material handling equipment such as stacker reclaimers, crushers, haulages, ball mills, cranes, hammer mills, rotary dryers, centrifuges, reciprocating pumps, winches, fans and wire drawing machines. 

Figure 10.17 shows an eight-stage 4-cm contactor. The motors are also face mounted, as discussed by Leonard (1988). There is only one leg between the two four-stage banks of contactors. In later units, one leg has been put at each end of each bank of contactors. This design makes it easier to handle individual banks of four contactor stages. A four-stage 10-cm contactor is shown in Figure 10.18. In this photograph, an overhead crane is lifting one of the motor/rotor assemblies out of the contactor housing.

Noise protection is needed to protect against RFI/EMI problems caused by mobile and stationary radio, television, and handheld walkie-talkies radio-controlled overhead cranes radar induction heating systems static discharge high-speed power-switching elements high-AC current conductors large solenoids and relays transformers AC and DC motors welders and even... 

Another major user is the steel industry, and Jost and Hicks and Forsythe described a wide variety of applications, including crane slewing plates, slideways, run-out table bearings, gears, work-roll bearings and motor bearings. In other industries the variety of applications is indicated by the list in Table 13.8. 

Power.—Power requirements of overhead cranes for hoisting, trolley and bridge motors depend upon speed of travel (minimum) and the load lifted (maximum capacity). The power of the motors are thus subject to selection to a certain extent and is governed by the Formulas (5a), (56) and (5c) ... 

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