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Breakdown torque happens when ′ / and such that / and thus, with constant voltage input, a low-slip induction motor's percent-rated maximum torque is about half its percent-rated LRC. The relative stator to rotor leakage reactance of standard Design B cage induction motors is [ 57 ]
A wound-rotor motor, also known as slip ring-rotor motor, is a type of induction motor where the rotor windings are connected through slip rings to external resistance. Adjusting the resistance allows control of the speed/torque characteristic of the motor.
As the slip increases, the skin effect starts to reduce the effective depth and increases the resistance, resulting in reduced efficiency but still maintaining torque. The shape and depth of the rotor bars can be used to vary the speed-torque characteristics of the induction motor.
As a result, the induction motor cannot produce torque near synchronous speed where induction (or slip) is irrelevant or ceases to exist. In contrast, the synchronous motor does not rely on slip-induction for operation and uses either permanent magnets, salient poles (having projecting magnetic poles), or an independently excited rotor winding ...
It includes a rotor spinning with coils passing magnets at the same frequency as the AC and produces a magnetic field to drive it. It has zero slip under typical operating conditions. By contrast induction motors must slip to produce torque. One type of synchronous motor is like an induction motor except that the rotor is excited by a DC field.
It is also known as short-circuit test (because it is the mechanical analogy of a transformer short-circuit test), [1] locked rotor test or stalled torque test. [2] From this test, short-circuit current at normal voltage , power factor on short circuit, total leakage reactance , and starting torque of the motor can be found.
Constant exciting current produces good linearity's between torque and slip frequency. In current control, the primary current is the control input to the induction motor whereas the primary terminal voltage is the control input in voltage control. Two transient phenomena are associated with induction motor operation.
Rotor slip provides necessary induction of rotor currents for motor torque, which is in proportion to slip. When rotor speed increases, the slip decreases. Increasing the slip increases induced motor current, which in turn increases rotor current, resulting in a higher torque for increase load demands. Wound rotor