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The hysteresis torque during the working of hysteresis motor depends on which factor?
Stator flux, rotor flux and sine of hysteresis angle
Stator flux only
Rotor flux only
Stator and rotor flux only
Stator flux, rotor flux and sine of hysteresis angle
The hysteresis torque in a hysteresis motor is produced due to the hysteresis lag between the stator revolving magnetic flux and the residual magnetism induced in the rotor. The torque is proportional to the product of the stator flux, the rotor flux, and the sine of the angle of lag between them.
The hysteresis torque in a hysteresis motor is produced due to the hysteresis lag between the stator revolving magnetic flux and the residual magnetism induced in the rotor. The torque is proportional to the product of the stator flux, the rotor flux, and the sine of the angle of lag between them.
Th=k⋅Φs⋅Φr⋅sin(δh) — where Th is hysteresis torque, Φs is stator flux, Φr is rotor flux, and δh is the hysteresis angle.
Ph=η⋅f⋅Bmaxn — Steinmetz hysteresis power loss formula where n is Steinmetz constant.
The stator produces a rotating magnetic field which induces eddy currents and hysteresis effects in the magnetically hard rotor material. Due to the hysteresis loop, the rotor flux lags behind the stator flux by a hysteresis angle δh. This spatial displacement generates a constant torque that is independent of the rotor speed until synchronous speed is reached.
Hysteresis torque is constant at all speeds from standstill to synchronous speed.
The rotor material must have high retentivity and high hysteresis loop area (e.g., cobalt steel).
It operates silently and with minimal mechanical vibrations compared to other single-phase motors.
The hysteresis angle δh is determined by the properties of the rotor material.
Extremely quiet operation
Constant torque from zero to synchronous speed
Low starting torque
Requires expensive magnetic materials for the rotor
Sound recording equipment
High-quality turntables and timing devices
The hysteresis angle is directly related to the area of the hysteresis loop, which represents the energy dissipated as heat per cycle.
Option B, C, and D are incorrect because they ignore the phase relationship (the hysteresis angle) which is fundamental to the production of electromagnetic torque in this motor type.
A is correct — The hysteresis torque depends on the stator flux, rotor flux, and the sine of the hysteresis angle as defined by the torque equation Th=kΦsΦrsin(δh).
Always remember that unlike induction motors, the hysteresis motor develops a uniform torque at all speeds, making it ideal for constant-speed applications.
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