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# Download Electrical Principles III by Noel M. Morris (auth.) PDF

By Noel M. Morris (auth.)

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Determine the percentage change in the armature speed from its original value. f. c. 016 Wb and the armature speed is 900 rev/min. f. 002 Wb and the speed is increased to 1200 rev/min. c. 42 m. 7 T (the remaining conductors can be assumed not to be in a magnetic field). Determine the torque produced when the armature current is 20 A. c. c. generator. c. 7 at 440 V. c. generator delivers a current of 70 A at 110 V. Calculate the overall efficiency of the motor-generator set. c. motor the current was 15 A at 250 V.

One way of doing this is to increase the brush contact resistance; this is brought about by using brushes with a relatively high value of resistance (carbon brushes are used), and the resistance of the 'skin' or film on the surface of the commutator (this forms with use) also aids commutation. 6a). mJ. is such as to oppose the self-induced voltage in the coil due to armature current commutation. f. ofthe self-induced commutation voltage is also related to it), hence the interpole windings are arranged to carry the armature current.

2 A single-phase transformer has a voltage step-down ratio of 4: 1 and the high voltage winding is supplied at 440 V. 6 lagging. Neglecting the effects of losses, calculate (a) the rating of the transformer, (b) the power supplied to the load and (c) the primary winding current. 3 A single-phase transformer has a step-down voltage ratio of 10: 1. 8 power factor lagging. Neglect the effects of the internal impedance of the transformer. 713. Determine the value of the no-load current. Neglect the effects of the impedance of the windings.