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The losses occurring in a d.c. motor are the same as in a d.c. generator (i) copper losses (ii) Iron losses or magnetic losses (iii) mechanical losses As in a generator, these losses cause (a) an increase of machine temperature and (b) reduction in the efficiency of the d.c. motor. The following points may be [...]
Written by John on September 19th, 2009 with 1 comment.
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Since the armature of a motor is the same as that of a generator, the current from the supply line must divide and pass through the paths of the armature windings. In order to produce unidirectional force (or torque) on the armature conductors of a motor, the conductors under any pole must carry the current [...]
Written by John on September 18th, 2009 with 2 comments.
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As in a d.c. generator, armature reaction also occurs in a d.c. motor. This is expected because when current flows through the armature conductors of a d.c. motor, it produces flux (armature flux) which lets on the flux produced by the main poles. For a motor with the same polarity and direction of rotation as [...]
Written by John on September 16th, 2009 with no comments.
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For any motor, the torque and speed are very important factors. When the torque increases, the speed of a motor increases and vice-versa. We have seen that for a d.c. motor; N = K (V- IaRa)/ Ф = K Eb/ Ф…………………………………………….(i) Ta α ФIa…………………………………………………………………………(ii) If the flux decreases, from Eq.(i), the motor speed increases but [...]
Written by John on September 16th, 2009 with no comments.
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Eb = V-IaRa But Eb=PФZN/60A PФZN/60A = V- IaRa Or N = (V- IaRa)/ Ф × 60A/ PZ Or N = K (V- IaRa)/ Ф But V- IaRa = Ea Therefore N= K Eb/ Ф Or N α Eb/ Ф Therefore, in a d.c. motor, speed is directly proportional to back e.m.f. Eb and inversely [...]
Written by John on September 14th, 2009 with 1 comment.
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The torque which is available at the motor shaft for doing useful work is known as shaft torque. It is represented by Tsh. Fig. (4.9) illustrates the concept of shaft torque. The total or gross torque Ta developed in the armature of a motor is not available at the shaft because a part of it [...]
Written by John on September 14th, 2009 with no comments.
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Torque is the turning moment of a force about an axis and is measured by the product of force (F) and radius (r) at right angle to which the force acts i.e. D.C. Motors torque T = F × r In a d.c. motor, each conductor is acted upon by a circumferential force F at [...]
Written by John on September 13th, 2009 with no comments.
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Like generators, there are three types of d.c. motors characterized by the connections of field winding in relation to the armature viz.: (i) Shunt-wound motor in which the field winding is connected in parallel with the armature [See Fig. 4.4]. The current through the shunt field winding is not the same as the armature current. [...]
Written by John on September 8th, 2009 with no comments.
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Let in a d.c. motor (See Fig. 4.3), V = applied voltage Eb = back e.m.f. Ra = armature resistance Ia = armature current Since back e.m.f. Eb acts in opposition to the applied voltage V, the net voltage across the armature circuit is V- Eb. The armature current Ia is given by; Ia = [...]
Written by John on September 4th, 2009 with no comments.
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When the armature of a d.c. motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator The induced e.m.f. acts in opposite direction to the applied voltage V(Lenz’s law) and in known as back or counter e.m.f. [...]
Written by John on September 4th, 2009 with 1 comment.
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