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Electric End Uses
Published in J. Lawrence, P.E. Vogt, Electricity Pricing, 2017
AC motors also operate on the principle of magnetic attraction and repulsion and are based on rotating magnetic fields. When an AC voltage is applied to the terminals of the stator pole windings, the resulting current flows through the windings in a sinusoidal fashion. As a result, a pulsating magnetic field is created between the north and south poles. The magnetic field reaches full intensity when the current is at its maximum value. When the winding current changes direction at every half cycle, the direction of the magnetic field between the pair of poles changes by 180° (i.e., the north and south poles exchange places). Thus, the magnetic field revolves in circular fashion. A bar magnet located between the poles would spin in order to align its fixed north and south poles with the stator’s rotating magnetic field. The magnet would continue to turn in synchronism with the revolving stator field, and torque would be produced. In an AC motor, the “magnet” is the rotor. Although both magnetic fields rotate, the rotor field is stationary with respect to the stator field.
Applied engineering systems
Published in Mike Tooley, Engineering A Level, 2006
The principle of all AC motors is based on the generation of a rotating magnetic field. It is this rotating field that causes the motor’s rotor to turn. AC motors are generally classified into two types:synchronous motorsinduction motors.
Electric Vehicles
Published in Arumugam S. Ramadhas, Alternative Fuels for Transportation, 2016
Nallusamy Nallusamy, Paramasivam Sakthivel, Abhijeet Chausalkar, Arumugam Sakunthalai Ramadhas
Commutatorless motor drives offer a number of advantages over conventional DC commutator motor drives for the electric propulsion of hybrid EVs. AC induction motor drives have additional advantages such as being lightweight in nature, small volume, low cost, and high efficiency. Generally the AC motors fall under three categories: induction motors, synchronous motors, and switched or variable reluctance motors.
Variable frequency drive harmonics and interharmonics exciting axle torsional vibration resulting in railway wheel polygonisation
Published in Vehicle System Dynamics, 2020
The rotational speed of an AC motor is dependent on the frequency of the electrical power supplied to the motor and therefore its rotational speed can be altered by means of a variable frequency drive (VFD). The VFD is normally not connected to a pure DC power source but rather follows the process illustrated in Figure 2(a). A single-phase AC supply is drawn by the locomotive (under AC catenary) after which it is rectified and filtered to approximate a constant DC voltage supply. Alternatively, the DC voltage supply can be drawn directly from the overhead catenary. The DC supply voltage in most practical applications is not perfectly constant as shown in Figure 2(b) and may still contain fluctuating artefacts from the rectification process. The DC supply is inverted to a 3-phase AC output by the VFD. The VFD is able to control the frequency of the AC output and thus control the motor speed.