Variable speed motors

Screen drive motor Variable speed coupling... 

Most of the drivers used with the sliding vane compressor are electric motors. Variable speed operation is possible within the limits of vane speed requirements. The vanes must travel fast enough to seal against the cylinder wall but not so fast that they cause excessive wear. For the smaller units, under 100 hp, V-belts are widely used. Direct connection to a motor, however, is possible for most compressors and is used through out the size range. 

Variable Speed Drive. This can be accomplished by turbines, direct current motors, variable-speed motors, or slip-ring motors. With the changing speed of the driver, the fan output capacity and pressure can be varied. For capacity reductions below 50%, an outlet damper is usually added to the system. 

Agitator Turbine, 3.6 HP, 1750 rpm, XP rated motor, variable speed drive Circulating pump Viking series HL124, 2 HP, 1745 rpm, XP rated motor Micro Motion mass flow meter stainless steel 316L, 0-80 lb/min mass flow range, accuracy of 0.4% of range, XP rated with electronics unit mounted separately in nonhazardous area. 

Operate system throughout the range of operating design specifications or range of intended use. Verify switches and push-buttons, rotator direction, motor variable speed, supply temperature, differential pressure, and pan air flow. 

Power supply Electric motor Variable speed... 

Various standard types AC motors are used e.g. squirrel-cage and wound rotor induction motors, variable speed commutator AC motors. 

Electric motors, variable speed TEFC 1800 rpm plus V-belt unit for speed control 2/1 to 5/1 at 3480, 520 and 30 rpm. FOB cost = 8000 at the ratio of (drive power... 

Centrifuge, continuous extraction, 316 s/s including flexible connedions, explosion-proof motor, variable speed drive, ammeter, tachometer, excluding pumps, starter, flowmeters and control valves. FOB cost 220,000 at aqueous feed rated capacity = 2.2 L/s with n = 0.25 for the range 0.03-2.2 and n = 0.38 for the range 2.2-36. L-i-M = 1.70. L/M = 0.96. 

Typically in the lower torque range (geared hoist drives), the preference is for squirrel-cage induction motors. Variable speed drive application allows for Optimum Pole design of the motors, where the number of motor poles is selected by taking into account the torque density, power factor and speed range, rather than the maximum operating speed for a fixed frequency. 

Figure 2. Experimental set-up for slurries. 1, screw feeder 2, rotary drum (lucite) 3, rubber-lined rollers 4,1/4-hp motor (variable speed) 5, slurry collecting tank 6, rotameter 7, positive displacement pump 8, fluid tank V, valve.

Main drive motor, variable-speed thyristor-fed DC motor designed to a rating about 100% above the theoretical power demand. 

Pumps are driven by either fixed-speed or variable-speed motors. Variable-speed motors are becoming increasingly common. Flow can be controlled by varying the pump speed with the motor and thus eliminating parasitic energy losses across a flow control valve. However, because of the extra electronic components needed for a variable-speed AC motor, 95 percent of the motors we work with are fixed-speed alternating-current motors. I will only discuss fixed-speed, alternating-current (AC) motors in this chapter. 

A powerful stirrer, driven by a flexible driving shaft between the motor (I h.p.) and the stirrer, is depicted in Fig. II, 7, 3. The motor may be placed at a distance from the stirrer head and reaction vessel, thus enabling the assembly to be used for inflammable, corrosive or fuming liquids without damage to the motor. Furthermore, any laboratory retort stand and clamp may be used since the stirrer head weighs only about 250 grams. A variable speed control (500-2000 r.p.m.) is provided. 

Variable Air Flow Fans. Variable air flow fans are needed ia the process iadustry for steam or vapor condensing or other temperature critical duties. These also produce significant power saviags. Variable air flow is accompHshed by (/) variable speed motors (most commonly variable frequency drives (VFDs) (2) variable pitch fan hubs (J) two-speed motors (4) selectively turning off fans ia multiple fan iastaHations or (5) variable exit louvers or dampers. Of these methods, VFDs and variable pitch fans are the most efficient. Variable louvers, which throttle the airflow, are the least efficient. The various means of controlling air flow are summarized ia Table 3. 

In 1840 a hydrauHc power network, which involved large reciprocating pumps that were driven by steam engines, suppHed fluid power to London. However, concurrent technology in steam (qv) turbines and the electric generators outmoded such networks until hydrauHc systems were improved with the use of rotary pumps and oil. The rotary piston pump marked the transition from use of water to oil as the hydrauHc fluid (4). The use of vacuum-distilled, refined mineral oils were instmmental in the success of rotary axial piston pumps and motors such as the Waterbury variable speed gear... 

Many improvements have been made to streamline performance and to reduce machine operation labor. Some of these are tensionless jigs using variable speed electric motors with built-in drag for brakes, automatic reversing equipment, and automatic temperature and level controls. These machines are widely used for goods that are easily creased, such as fabrics consisting of filament acetate, heavy filament nylon, or cotton duck. They are also convenient for small dye lots and for sampling purposes. 

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. 

In addition to energy conservation, the variable speed drives offer better control because of a faster response, ie, reduced dead band. They are also sometimes chosen for safety reasons because of elimination of the control station and accompanying valving. The capital saved by use of a smaller motor and elimination of the control valve partially compensates for the cost of the drive. 

The centrifugal pump directly driven by a variable-speed electric motor is the most commonly used hardware comoination for adjustable speed pumping. The motor is operated by an electronic-motor speed controller whose function is to generate the voltage or current waveform required by the motor to make the speed of the motor track the input command input signal from the process controller. 

Throttle discharge of running pump until spare can get in system. Slow down running pump if it is a turbine or variable-speed motor. 

Air-Flow Control Process operating reqmrements and weather conditions are considered in determining the method of controlling air flow. The most common methods include simple on-off control, on-off step control (in the case of multiple-driver units), two-speed-motor control, variable-speed drivers, controllable fan pitch, manually or automatically adjustable louvers, and air recirculation. 

Inverters make it possible to control a variable-speed fan by changing the frequency modulation. Standard alternating-current fan motors may be speed-regulated between 0 and 60 Hz. In using inverters for this apphcation, it is important to avoid frequencies that would result in fan critical speeds. 

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