Motors and Drive Systems

The availability of power and torque to the shank of the screw is extremely important to the success of an extrusion process, especially if modifications to the line are planned to increase the rate. That is, the proper level of power must be available at the proper screw speed. Thus, the motor size and speed, belt sheaving if used, and gearbox reduction must be specified to provide enough power to the screw to plasticate and pump the resin at a high rate. 

The electrical current used by the motor is an important indicator of the performance of the extruder. The current as measured in amperage is directly proportional to the torque applied to the motor shaft and also to the screw. The motor current can be used to estimate the power and specific energy that are dissipated by the screw. The variation in the motor current with time is also an indicator of the stability of the extruder. Numerous examples of the motor current stability and process stabilities are presented in Chapter 12. 

The rotation speed of the screw to that of the motor is simply  

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Due to the balance between hoist and balance ropes, Koepe hoists require significantly less torque compared with a drum hoist of similar capacity. This results in reduced capital costs due to smaller motors and drive systems, and reduced operating costs due to power consumption. 

Air-cooled condensers for cold climates may require protection from freezing. Louvers, fans, motors, and drive systems should be top quality with adequate safety factors. Several methods are used to prevent freezing in cold climates ... 

However, this power loss is just the power delivered to the rotor of the compressor. This power comes from an electric motor, which has an efficiency of less than 1, and there are also losses in the connecting shaft and the bearings of the compressor rotor. If we express the combined efficiency of the motor and drive system as r m, then Ihe electrical power used will be greater than the compressor power by a factor of I/rjm, and so there will be a loss of electrical power given by the equation... 

Determination of Reliability Characteristic Factors in the Nuclear Power Plant Biblis B, Gesellschaft fur Reaktorsicherheit mbH Nuclear Failure rates with upper and lower bounds and maintenance data for 17,000 components from 37 safety systems Data for pumps, valves, and electrical positioning devices, electric motors and drives from an operating power plant 66. 

Figure 14-2C. Siemens form wound stator with Siemens MICLAD-sealed epoxy mica insulation system. (Used by permission Bui. M DD 3323 1994, Siemens Corporation, Motors and Drives Division.)...

The best approach to implement a motion control system is to first specify a motor and drive that are capable of meeting the performance requirements. Once they are specified, the remaining parts of the system should be selected to match the motor and drive combination. In addition to the performance of the control axis, networking capability, user interface, and environmental considerations should also be addressed. 

Rotary drum filter, vacuum, c/s with swing agitator, panel or wire-wound drum, wash apparatus, variable speed drum drive, trunions, stuffing boxes, scraper discharge, motor and drive excluding vacuum system and vacuum receiver. FOB cost = 210000 for a total drum, nDL, area = 22 m with n = 0.25 for the range 2-22 and n = 0.7 for the range 22-200. FOB cost = 210 000 for an effective filter area =... 

Although relatively efficient, the heat generated from these transformers has resulted in complex ventilation and cooling equipment requirements to cool the transformer room. Transformers designed for outdoor installation or hquid cooled transformers designed to be part of the coohng system for the motors and drives should be considered. 

Means to drive the belt/chain and driving system for top pulley gear box and electric motor. The system should be designed for at least 150-200% of fully loaded condition at maximum speed. 

Conventional back-drive systems on decanters perform a braking duty. As such many of them have the ability to regenerate power. Although an eddy current brake is unable to do this. AC. DC. and inverter motors, and hydraulic systems are. The braking process causes the electric motor to act as a generator and so returns power to the grid. In the case of the DC and inverter motor, the power regenerated is usually considered dirty unless electric filters are fitted which smooth out unwanted harmonics. 

It consists of a stepper motor drive system and a valve coupled with stepper motor. The drive system accepts 4-20 mA current signal from the controller and generates proper sequence of position signals proportional to the modulus of the deviation of the control signal from 12 mA. The stepper motor operated valve has been used successfully for primary and secondary air control in a sulphur furnace, condensates control in desuperheater, SO2 control in sulphiter, imbibition water temperature control etc. 

Some results of the constant-value pricing system are as foUow generation in a central unit at relatively low pressure, <4.24 MPa (600 psig) tremendous economic pressure to use turbines rather than motors for drives lack of incentive for high efficiency turbines excessively high temperature differentials in steam users tremendous incentive to recover waste heat as low pressure steam and a large plume of excess low pressure steam vented to the atmosphere. 

Pneumatic systems use the wave motion to pressurize air in an oscillating water column (OWC). The pressurized air is then passed through an air turbine to generate electricity. In hydrauhc systems, wave motion is used to pressurize water or other fluids, which are subsequendy passed through a turbine or motor that drives a generator. Hydropower systems concentrate wave peaks and store the water dehvered in the waves in an elevated basin. The potential energy suppHed mns a low head hydro plant with seawater. 

Hydraulic-drive samplers are also available, but cost factors tend to be substantially greater than electromechanical units. Recent use of hydraiilic-drive systems has diminished with the availability of increased strength and durabihty electric-motor linear-drive units capable of reliable operation in high-capacity applications. 

The number of speed reduetions is another way to classify conveyor drives. Most common of the speed-reduction methods is the two-step system, in which the motor is coupled to a speed reducer and the slow-speed shaft of the reducer is connected to the conveyor-drive shaft by a V belt or a roller chain. The second reduction not only permits the use of a simpler speed reducer but also allows a more flexible layout of the motor and reducer mounting plate. On many installations this eliminates the need for a specially designed drive mount. 

The great flexibility of dc motors both through inherent design charac teristics and through the way in which they are operated makes them ideally suited to adjustable-speed drives, particularly regulated drive systems. 

Direct-Current Motor Control Control for dc motors runs the gamut from simple manual line starters to elaborate regulating systems. Only the starting problems are considered here since variable-speed drives and regulating systems are discussed elsewhere. 

Although motors and controllers can be bought separately, the trend is to purchase a system from a given manufacturer. There are six types oi variable-speed drives, as own in F ig. 29-73. Dynamic response indicates the ability of the drive to respond to a change in command it is measured in radians/second the higher the number, the faster the drive response. 

The power from the motor shaft to the driven shaft can be transmitted in many ways, depending upon the power and load application. In this chapter we deal with the most common types of driving systems, their influence on the starting characteristics of the motor and their effect on bearings. 

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