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Generators and motors
Published in David Wyatt, Mike Tooley, Aircraft Electrical and Electronic Systems, 2018
We have already shown how a rotating magnetic field is produced when a three-phase alternating current is applied to the field coils of a stator arrangement. If the rotor winding is energized with DC, it will act like a bar magnet and it will rotate in sympathy with the rotating field. The speed of rotation of the magnetic field depends on the frequency of the three-phase AC supply and, provided that the supply frequency remains constant, the rotor will turn at a constant speed. Furthermore, the speed of rotation will remain constant regardless of the load applied. For many applications this is a desirable characteristic; however, one of the disadvantages of a synchronous motor is that it cannot be started from a standstill by simply applying three-phase AC to the stator. The reason for this is that the instant AC is applied to the stator, a high-speed rotating field appears. This rotating field moves past the rotor poles so quickly that the rotor does not have a chance to get started. Instead, it is repelled first in one direction and then in the other.
Electric End Uses
Published in J. Lawrence, P.E. Vogt, Electricity Pricing, 2017
In an induction motor, an AC voltage source is applied to the stator only while the rotor is not connected electrically to the source. The current flow in the stator windings induces a current flow in the rotor as the lines of magnetic flux cut across the rotor windings. The induced rotor current produces a rotating magnetic field having the same number of poles as the stator. The rotor field rotates at the same speed as the stator field so torque is produced. But the speed of the rotor itself is less than the synchronous speed of the rotating magnetic fields.7 The difference between the synchronous speed and the rotor shaft speed is referred to as slip, and it is usually expressed as a percent of the synchronous speed.
Spindle Motor Control
Published in Abdullah Al Mamun, GuoXiao Guo, Chao Bi, Hard Disk Drive, 2017
Abdullah Al Mamun, GuoXiao Guo, Chao Bi
It shows that, the rotational speed of the MMF or of the airgap flux density is proportional to the frequency of the current, and inversely proportional to the pole-pair of the magnetic field. In other words, a rotating magnetic field can be generated by inputting the 3-phase time-symmetric alternating currents into the 3-phase space-symmetric windings. This is an electrical method to realize the rotational field. The field speed can be adjusted by changing the frequency of the current. Otherwise, for a given frequency of the current in the winding, the speed of the rotating field can be designed with a suitable magnetic pole-pair in the motor design stage.
Vector-Controlled Dual Stator Multiphase Induction Motor Drive for Energy-Efficient Operation of Electric Vehicles
Published in IETE Journal of Research, 2023
M. Sowmiya, S. Hosimin Thilagar
The drive is built to operate in three different modes. The first mode involves the excitation of the inner stator when the load demand is low, and the second mode involves the excitation of the outer stator when the load demand is high. During the excitation of the single stator, a rotating magnetic field is developed in the air gap between the excited stator and the rotor cage, this field is responsible for the production of torque. For any further raise in load demand, excitation of both stators is done under the third mode. During this mode of operation, a synchronized five-phase power supply is essential at both the stator windings to achieve a synchronized rotating flux pattern. This flux assists in the vector sum of torque developed by both stators. Thus, the net torque developed is capable of supporting a high load demand which is greater than the rated torque developed during individual stator excitations.
Magnetoresistance sensor-based rotor fault detection in induction motor using non-decimated wavelet and streaming data
Published in Automatika, 2022
S. Kavitha, N. S. Bhuvaneswari, R. Senthilkumar, N. R. Shanker
The proposed GBR method identifies broken rotor bar faults by the analysis of the outward magnetic field. The balanced three-phase IM always generates a clockwise rotating magnetic field under healthy operating conditions. There is no anti-clockwise field for a healthy electric motor [44]. An anti-clockwise magnetic field generated by the motor during rotor faults is due to the imbalance of rotor bar currents. Hence, analysis of the anti-clockwise outward magnetic field can identify the rotor bar faults detection. The anti-clockwise outward magnetic is due to motor axial and transverse components. Hence, the outward anti-clockwise magnetic field is measured based on axial-radial decomposition characteristics [45]. According to the axial-radial position of the motor, the sensor is placed at the outer stator position along the rotor axis and monitors the outward magnetic field with minimum effect of the transverse field.
Boundary conditions of active steering control of independent rotating wheelset based on hub motor and wheel rotating speed difference feedback
Published in Vehicle System Dynamics, 2018
Yuanjin Ji, Lihui Ren, Jinsong Zhou
Compared with traditional motor, permanent-magnet synchronous motors use permanent magnets instead of windings. When a three-phase symmetrical current is passed through the stator armature winding, a rotating magnetic field is formed. Because a magnetic field tends to align with itself, an interactive force is generated separately from the magnetic fields of the stator armature winding and the permanent magnet, and electromagnetic torque is produced to drive the rotation of the rotor. Due to their high power-mass ratio, high energy efficiency, and excellent servo performance, permanent-magnet synchronous motors are widely applied in electric vehicles and railway vehicles.