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Centrifuge modelling: practical considerations
Published in R.N. Taylor, Geotechnical Centrifuge Technology, 2018
Electric motors are normally best orientated with their main rotor axis in line with the centrifuge acceleration field. The increased rotor weight can then be carried through thrust bearings attached to the motor output shaft. The rotor will flex when placed across the acceleration field. This flexure and the radial play in the rotor supports may permit the rotor and stator to short. The type of electric motor and controller to use is dependent on the power, speed and control requirements of the model test. Generally, three-phase electric motors are preferable to single-phase motors as they have a higher power-to-frame size ratio and radiate less electrical noise. Permanent magnet motors are beneficial due to their simple construction and reduced number of electrical connections. Brushless servo-motors have an excellent power-to-frame size ratio and a simple construction, but require a sophisticated electronic controller and power amplifier.
DC machines
Published in William Bolton, Engineering Science, 2020
The speed of a permanent magnet motor depends on the current through the armature coil and thus can be controlled by changing the armature current. With a field coil motor the speed can be changed by either varying the armature current or the field current; generally it is the armature current that is varied. Thus speed control can be obtained by controlling the voltage applied to the armature. Figure 18.9 shows circuits that can be used when a variable resistor is used. This method is, however, very inefficient since the controller resistor consumes large amounts of power. Another alternative is to control the voltage by using an electronic circuit.
Sensitivity-Based Design and Optimization of Line Start Synchronous Reluctance Motor
Published in Electric Power Components and Systems, 2023
Abakar Limane Mahamat, Emre Gözüaçık, Mehmet Akar
Due to the increase in energy consumption in the world and the decrease in energy resources, the need for new energy sources is also increasing. Electrical energy is one of these energy sources [1]. Electric motors and drives consume approximately 40% of the electrical energy generated. In industrial applications, electric motors account for 70% of the consumption [2, 3]. In this case, it can be said that one way to save electrical energy is to increase the efficiency of electric motors, which are an important part of consumption. The most widely used motor type in the world is induction motors (more than 90%) which are low cost, robustness, do not need a driver and can be driven directly from the line. In addition, permanent magnet motors have been widely used in applications requiring high efficiency, high torque, high power density, and simple control [1, 4]. The high price and limited market availability of rare earth magnets negatively affect the use of magnet motors. The winding losses in the rotor and winding-related thermal disadvantages of induction motors make synchronous reluctance motors (SynRM) a good alternative [5]. SynRMs have preferred in industrial and automotive applications due to their low cost, easy production, simple structure, field weakening capability, low loss, and high torque-to-volume ratio [1].
Polder pumping-station for the future: designing and retrofitting infrastructure systems under structural uncertainty
Published in Sustainable and Resilient Infrastructure, 2022
Jos Timmermans, Emiel van Druten, Marcel Wauben, Jan Kwakkel
Evaluation of cost performance is based on investments, operational, indirect, and electricity costs. According to the feature scoring of Figure 5, investment costs are sensitive to the number of pumps, pump type in relation to fish safety, and motor choice, while operational costs are sensitive to the energy scenarios and electricity costs are determined primarily by the solar/wind mix. For number of pumps and fish safe solutions, we already concluded under functional performance and ecological performance that installing two pumps while maintaining the existing gas engine and pump, and installing fish safe impellers results in the most robust design. Currently, the more efficient permanent magnet motors are cheaper than the often-installed induction motors. Moreover, permanent magnet motors are smaller, lighter, have a broader efficient working range and require less maintenance and thus have lower operational costs than induction motors. Based on these advantages permanent magnet motors are advised for pumping station Vissering. Furthermore, from the perspective of cost performance, the investment costs of improved pump inflow are so minor as compared to their benefit in improving energy efficiency that they should be, like permanent magnet motors, be included in all designs and are robust under all scenarios.
Developments and clinical evaluations of robotic exoskeleton technology for human upper-limb rehabilitation
Published in Advanced Robotics, 2020
Akash Gupta, Anshuman Singh, Varnita Verma, Amit Kumar Mondal, Mukul Kumar Gupta
Of the above-listed actuators, Electric Motors are the commonest choice [1,76] due to their ease of control, actuation, maintenance, compactness, and portability. However, they are held back because of the high impedance values. The pneumatic actuators composed of the pneumatic cylinder offers high power to weight ratio if the weight of the compressor unit required for cylinder actuation is not considered. The hydraulic actuators are the most powerful among the above mentioned, but it is relatively heavier and suffers from fluid leakage problems, which is not suitable for rehabilitation application. Another innovation in the field of actuators is pneumatic muscle actuators [77]. These actuators have a very good power/weight ratio like pneumatic actuators and exhibit the properties of the human muscle system [78]. They are light and transfer force in a single direction with the help of internal rubber structure and braided mesh shell [1]. Electric motors are the most widely used actuators in upper and lower limb exoskeletons due to their reliability, favorable torque to weight ratio, high speed, good overloading capacity, and precision. There are two types of electric actuators: AC motors and DC motors, mostly brushless. Because permanent-magnet motors provide high torque despite the motor shaft being stationary, they are preferred by most in the industry. In the case of mobile exoskeleton devices, a lightweight motor is ideal to use. Brushed DC motors provide high torque, high efficiency, and performance [79].