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A universal motor is said to be inductively compensated when compensating winding:

A universal motor is said to be inductively compensated when compensating winding: Correct Answer is short circuited on itself

The following modifications are made in a dc series motor that is to operate satisfactorily on the alternating current:

  • The field core is constructed of a material having low hysteresis loss. It is laminated to reduce eddy-current loss.
  • The field winding is provided with a small number of turns. The field-pole area is increased so that the flux density is reduced. This reduces the iron loss and the reactive voltage drop.
  • The armature of a universal motor is of the same construction as an ordinary series motor.
  • To minimize commutation problems, the universal motors are designed with high resistance brushes with increased brush area & moderate magnetic field.
  • The number of armature conductors is increased to get the required torque with the low flux.
  • To reduce the effect of armature reaction, thereby improving commutation and reducing armature reactance, a compensating winding is used.
  • The compensating winding is put in the stator slots. The axis of the compensating winding is 90° (electrical) with the main field axis. It may be connected in series with both the armature and field as shown in the figure below. In such a case the motor is conductively compensated.


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The compensating winding may be short-circuited on itself, in which the motor is said to be inductively compensated.

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Applications:

  • Universal motors are used as portable drills, hairdryers, grinders, table-fans, blowers, polishers, kitchen appliances, etc.
  •  They are also used for many other purposes where speed control and high values of speed are necessary.
  • The universal motor is simple in construction and cheap. It is used usually for rating not greater than 750 W

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