Models 5E, 5F, 5G & 5H Electric Switch Machines: Single ... - Alstom

Theory of Operation2.5.1.2. Magnetic DetentAt the completion of each stroke, the overrun of the motor generates a current. Thiscurrent flows through a low-resistance circuit. Flux generated in this circuit quickly slowsand stops armature rotation.• In Models 5E and 5F, the circuit includes the snub-resistor lead, one-half of the snubrectifier, point-detector contacts, and the opposite field coils of the motor.• In the Models 5G and 5H, the circuit includes the snub-resistor lead, one-half of thesnub rectifier, the snub contact in the controller, and the opposite field coils of themotor.The holding device magnetically locks the motor armature when it is not rotating. Apermanent ring magnet is fixed to the housing cover while a similar magnet is attachedto the armature shaft. These magnets, shown in Figure 2–11, slow the motor to preventunwanted armature rotation after energy is removed from the motor.With the motor de- energized, the poles of the armature magnet line up with the poles ofopposite polarity in the fixed magnet. A magnetic detent effect, produced by a magneticfluxlinkage between the magnetic poles, prevents armature rotation.Figure 2-11. Schematic Diagram of Holding Device,Showing Magnetic Detent EffectP1293, Rev. Jun/07 2–12 Alstom Signaling Inc.