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The universal motor is modified in several ways to allow for proper AC supply operation. There is a compensating winding typically added, along with laminated pole pieces, as opposed to the solid pole pieces found in DC motors. [2] A universal motor's armature typically has far more coils and plates than a DC motor, and hence fewer windings per ...
The difference, or "slip," between actual and synchronous speed varies from about 0.5% to 5.0% for standard Design B torque curve induction motors. [30] The induction motor's essential character is that torque is created solely by induction instead of the rotor being separately excited as in synchronous or DC machines or being self-magnetized ...
is the torque produced divided by armature current. [10] It can be calculated from the motor velocity constant . = = = where is the armature current of the machine (SI unit: ampere).
Motor speed can be changed because the motor's torque curve is effectively modified by the amount of resistance connected to the rotor circuit. Increasing resistance lowers the speed of maximum torque. If the resistance is increased beyond the point where the maximum torque occurs at zero speed, the torque is further reduced.
By adjusting the shape of the bars in the rotor, the speed-torque characteristics of the motor can be changed, to minimize starting current or to maximize low-speed torque, for example. Squirrel-cage induction motors are very prevalent in industry, in sizes from below 1 kilowatt (1.3 hp) up to tens of megawatts (tens-of-thousand horsepower).
The drive speed decreases when the counter-torque is higher than the driving torque. At the operating point, the driving torque and the counter-torque are balanced, so the speed does not change anymore. A speed change in a stable operating point creates a torque change which acts against this change of speed.
Brushed DC motors can be varied in speed by changing the operating voltage or the strength of the magnetic field. Depending on the connections of the field to the power supply, the speed and torque characteristics of a brushed motor can be altered to provide steady speed or speed inversely proportional to the mechanical load.
The horizontal axis shows the rotational speed (in rpm) that the crankshaft is turning, and the vertical axis is the torque (in newton-metres) that the engine is capable of providing at that speed. Torque forms part of the basic specification of an engine: the power output of an engine is expressed as its torque multiplied by the angular speed ...