The Physics Of Mechanical Materials

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dges The wedges that hold the rotor winding in the slots are sometimes also complex in design, but always highly stresses. The wedges must hold the copper winding and its insulation systems in place at high rotational speeds and allow cooling gas to pass through them. This one reason why at the wedges there are higher stresses. The wedges generally have cooling vents machined into them, which reduces their effective strength. High cooling gas temperatures can also affect wedge strength if the temperatures begin to affect the creep life of the material. The wedges are generally made of lightweight materials, such as aluminum or brass, in the winding slots. This area does not generally carry the useful magnetic lux, so the wedges do not need to be made of magnetic material. AMORTISSEUR WINDING Most modern rotors employ a damper or amortisseur or damping winding to dampen torsional oscillations and provide a path for induced currents to flow. The amortisseur winding is essentially a separate winding installed under the rotor wedges and retaining-rings that is connected similar to the squirrel-cage of an induction motor. It produces an opposing torque when currents flow in it, and this helps dampen torsional oscillations and add to the stability of the rotor during system stress events. In some instances, where full-length aluminum wedges are used in the rotor, these may serve additionally as part of the damper winding. Also some designs use the
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