Drive motor speed

Weight of roH Weight of magnetic dutch Weight of drive shaft Total weight of rod, shaft, and clutch Water pressure load on rod, assuming approximately 40 lb/in. Drive motor power. Drive motor speed Water flow area (upper section) ... 

The hood pressure control system functions as follows When the pressure in the hood rises, which may occur for example as a result of a decrease in the exit gas flow or an increase in the cooling air flow, the controller increases the volume of air delivered by the exhaust air fan. It does this by adjustment of a damper or an inlet vane control unit or by varying the fan drive motor speed. Conversely, when the pressure in the hood goes down, the air delivery rate of this fan is reduced by the control system. Thus, with the aid of the hood pressure controller, the exhaust air fan performs the function of a pressure relief valve. 

Screen drive motor Variable speed coupling... 

The laboratory tubular centrifuge is similar to the industrial model. It operates with a motor or turbine drive at speeds to 50,000 rpm, generating 65,000 G at the latter speed in the 4.5 cm diameter bowl. The nominal capacity range is 30—2400 cm /min. This centrifuge is uniquely capable of separating far finer particles than any other production centrifugation equipment except the botde centrifuge. It is widely used in the production of flu vims. 

V ri ble Frecjuency Drives. An important energy by-product of soHd-state electronics is the relatively low cost variable speed drive. These electronic devices adjust the frequency of current to control motor speed such that a pump can be controlled direcdy to deUver the right flow without the need for a control valve and its inherent pressure drop. Eigure 11 shows that at rated load the variable speed drive uses only about 70% as much power as a standard throttle control valve system, and at half load, it uses only about 25% as much power. 

The most popiilar form of motor speed control for adjustable-speed pumping is the voltage-controlled pulse-width-modulated (PWM) frequency synthesizer and AC squirrel-cage induction motor combination. The flexibility of apphcation of the PWM motor drive and its 90 percent- - electric efficiency along with the proven ruggedness of the traditional AC induction motor makes this combination popular. 

Drive motors should be of the high-starting-torque type and selected for 1.33 times maximum rotational speed. For two- or three-diameter Idlns, the brake horsepower for the several diameters should be calculated separately and summed. Auxiliaiy drives should be provided to maintain shell rotation in the event of power failure. These are usually gasohne or diesel engines. 

One of the oldest adjustable-speed drives is the Ward-Leonard system. This consists of an ac to dc motor-generator set and a shunt or compound-wound dc motor. Speed is adjusted by changing the generator voltage. A functional equivalent of this drive uses an adjustable-voltage rectifier feeding a dc motor. This system has only one rotating machine in contrast to the three of a conventional Ward-Leonard system. 

Whenever the process machine operates at the same speed as its driver, the two can be directly coupled. This direct couphng stiU allows for a variable speed, through acuustments of the speed or the driver. Steam turbine speed can be easily adjusted, and electric motor speed can also be varied by the use of special drives that vaiw the frequency of the power applied to the motor. Wdiether the speed is fixed or variable, direci coupling of two machine shafts presents the problem of accommodation of misalignment. To this purpose, machines are coupled through a.flexible coupling. 

A100 kW, 750 r.p.m. motor drives a coal mill, having GDf as 600 kg.m through belts, at a speed of 500 r.p.m. Then its effective GDI at motor speed will be... 

With the use of statie drives for speed eontrol of induetion motors, through open or elosed-loop feedbaek eontrol... 

The time gap in carrying out the welding is compensated by raising the speed of the second route now introduced until the predefined buffer of an excess length of sheet is produced with the help of accumulator drive motor... 

For most of the rotary compressors in process service, the driver is an electric motor. Compressors in portable service, however, particularly the helical-lobe compressor, use internal combustion engines. Many of the rotary compressors require the high speed that can be obtained from a direct-connected motor. The dry type helical-lobe compressor is probably the main exception as the smaller units operate above motor speed and require a speed increasing gear which may be either internal or external (see Figure 4-1). The helical-lobe compressor is the most likely candidate for a driver other than the electric motor. Aside from the portables already mentioned, engines are used extensively as drivers for rotaries located in the field in gas-gathering service. Steam turbines, while not common, probably comprise most of process service alternate drive applications. 

Synchronous and induction motors cannot always be compared on an equal speed basis. In geared applications such as high-speed centrifugal compressor drives (above 3,600 rpm), the most economical induction moior speed is usually 1,800 rpm. The most economical synchronous motor speed for the same application might be 900 or 1,200 rpm, depend-... 

Most induction ac motors are fixed-speed. However, a large number of motor applications would benefit if the motor speed could be adjusted to match process requirements. Motor speed controls are the devices which, when properly applied, can tap most of the potential energy savings in motor systems. Motor speed controls are particularly attractive in applications where there is variable fluid flow. In many centrifugal pump, fan, and compressor applications mechanical power grows roughly with the cube of the fluid flow. To move 80 percent of the nominal flow only half of the power is required. Centrifugal loads are therefore excellent candidates for motor speed control. Other loads that may benefit from the use of motor speed controls include conveyers, traction drives, winders, machine tools and robotics. 

Normal electric motor speeds run from the standard induction speeds for direct connection of 3600, 1800 and 1200 rpm to the lower speed standards of the synchronous motors, and then to the somewhat arbitrary speeds established by V-belt or gear drives. For some cases, the pump speed is set by the type of drivers available, such as a gasoline engine. 

Variable speed drive (motor, turbine, hydraulic). 

For speed ranges of 3 to 1 or greater, adjustable-voltage operation is recommended. The adjustable-voltage drive usually includes a motor-generator set to supply an adjustable voltage supply to the armature of the drive motor. With this method of operation, a speed range of 10 to 1 readily obtained. 

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