Motor electric

Some of the factors that engfneets consider when selecting a motor for an application are (a) motor type, (b) motor speed (rpm), (c) motor performance in terms of torque output, (d) efficiency, (e) duty cycles, (f) cost, life eaqpectancy, (h) noise level, (i) maintenance and service requirements. Most of these are sdfeaqjlanatoiy. We discussed speed and torque in previous chapters next we will discuss motor types and duty cycles. 

Selecting a motor for an application depends on a number of fectors, including the speed of the motor (in rpm), the power requirement, and the type of load. Some applications deal with difficult starting loads, such as conveyors, while others deal with easy starting loads, such as a fen. For this reason, there are many diFferent types of motors. Here we will not discuss the principles of how various motors wodc. Instead, we will provide examples of various motors and their applications, as given in Table 12.3. Most of you will take some classes later that will be devoted to the theory and operation of motors. 

Split-phase Repulsion-stait induction CqKidnnr-stait r- R ulsion-induction Cq acitor-motor 

Load Motor iyp Starting Abilil7 Startii Current Siasel Phase Voltage 

Ea Starting Loads 1 to tunes nmniug torque 6 to 8 times running current (1/20-3/4 hp)  

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RCT are designed to successfully solve a whole number of tasks in nuclear power when testing fuel elements, in aviation and space industry when testing construction materials, nozzles and engine units, turbine blades and parts, in electromechanical industry-cables switching elements, electric motors in defense sphere- charges, equipment in prospecting for research of rock distribution and detection of precious stones in samples. 

One can also do work by stirring, e.g. by driving a paddle wheel as in the Joule experiment above. If tire paddle is taken as part of the system, the energy input (as work) is detemiined by appropriate measurements on the electric motor, falling weights or whatever drives the paddle. 

Mechanical Aerators. Mechanical aerators are modular ia design and built usiag electric motors. This type of aerator is also known as a surface splasher because it pumps water vertically iato the air. During this process the water is broken up iato small droplets allowiag exchange of oxygen from the air to the water. One type of mechanical aerator is shown ia Figure 3e. 

Horizontally Mixing Aspirator Aerators. An aerator using a horizontally mixing aspirator has a marine propeller, submerged under water, attached to a soHd or a hoUow shaft. The other end of the shaft is out of the water and attached to an electric motor. When the propeller is rotated at high velocity, at either 1800 or 3600 rpm, a pressure drop develops around the propeller. Air is then aspirated under the water and mixed with the water, and moved out. This type of aerator, shown ia Figure 3g, is very efficient ia mixing wastewater. 

Motor nd Drive. The preferred prime mover for a fan is usually an electric motor. Eor fans of low to moderate power, V-belt drives are frequently employed. This permits selection of fans that can be operated over a wide range of speeds rather than being limited to motor synchronous speeds. Furthermore, change of speed is less expensive with V-belt drives. However, fans requiring powerful motors, 37—75 kW (50—100 hp) and higher, are generally directly connected to the motor and driven at synchronous speed. 

Assemblies of small disks are rotated in a planetary movement around a central screw conveyor. The disks are mounted on six hoUow axles and the axles revolve on overhanging bearings from the gearbox at one end of the vessel where they are driven, via a drive shaft, by an electric motor. The filtrate is collected from the disks via the hoUow shafts and a filter valve into a large collecting pipe. The hoUow shafts also collect the water and air from the dewatering process, in another part of the rotational cycle. The number of disks mounted on the shafts can be adjusted for different materials, depending on the required capacity and the cake thickness to be used. 

The electrons, Hberated at the anode, travel by electrical cable through the external load, such as an electric motor, to the cathode. If the external circuit is open the reaction is stopped, no fuel is consumed, and no power is generated. The electrolytic reaction, then, is controlled by the load connected to the cell. The overall fuel cell reaction is... 

Cooling. A compression refrigeration system, driven by an electric motor, suppHes cooling for either direct expansion or ice bank systems (Fig. 12). In the former, the milk is cooled by the evaporator (cooling cods) on the bulk tank liner opposite the milk side of the liner. The compressor must have the capacity to cool the milk as rapidly as it enters the tank. 

Most rotating equipment includes electric motors or steam dryers that generate noise at a constant frequency. Air cooler fans are a source of noise that can be reduced by lowering the fan speed and increasing the number of blades. Pump motor noise can be reduced by including a shroud or fan cover that is accurately lined. Centrifugal compressor noise reduction can be achieved by blade design and the use of compressor pulsation noise reduction, silencers, and vibration isolation. 

An iajection mol ding machine is operated by hydrauHc power and equipped with an electric motor and hydrauHc pump. The maximum hydrauHc oil pressure is ca 14 MPa (2000 psi). A hydrauHc cylinder opens and closes the mold and holds the mold closed duriag iajection another cylinder forces the screw forward, thereby injecting the melt iato the mold. A separate hydrauHc motor turns the screw to plasticate, homogenize, and pressurize the melt. Control of these movements is a combined function of the hydrauHc and electrical systems (35—37). 

For a three-phase electric motor, the horsepower is calculated as... 

Various coupling designs are available to transmit torque from the driver, eg, electric motor, to a pump. In order to contain the pumped fluid inside the pump and prevent the pumpage from leaking, several types of sealing methods are used. A few options are described herein. 

Power, Energy, and Drives. Centrifuges accomplish their function by subjecting fluids and soHds to centrifugal fields produced by rotation. Electric motors are the drive device most frequently used however, hydrauHc motors, internal combustion engines, and steam or air turbines are also used. One power equation appHes to all types of centrifuges and drive devices. 

The electric motors are often the noisiest component of the centrifuge assembly. Most standard motors in the 75—250 kW range develop noise levels of 85 dbA (weighted sound pressure level using filter A, per the ANSI standard). A quiet motor can reduce this level by 5 dbA and should be used whenever noise is of concern. 

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