A 6 kV , 1000 kVA , 3-ph alternator is delivering full-load at 0.8 lagging. Its reactance is 20% and resistance negligible. By changing the excitation, the e.m.f. is increased by 25% at this load. Calculate the new current and power factor. The machine is connected to infinite bus-bars.

A 6 kV , 1000 kVA , 3-ph alternator is delivering full-load at 0.8 lagging. Its reactance is 20% and resistance negligible. By changing the excitation, the e.m.f. is increased by 25% at this load. Calculate the new current and power factor. The machine is connected to infinite bus-bars.

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.24P: For Problem 3.18, the motor operates at full load, at 0.8 power factor leading, and at a terminal...

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Concept explainers

Synchronous Motor

The synchronous motor is an AC electric type motor where at a steady-state the shaft rotation is synchronized with the supply current variable-frequency. To an integral number of AC cycles, the rotation period is exactly equal. The stator of the motor in the synchronous motor contains multi-phase AC electromagnets due to which a magnetic field is created that rotates in time with the oscillation of the line current. The rotor contains a permanent magnet and the rotor rotates in synchronization with the stator field at the same rate and provides the second synchronized magnetic field which is rotating in nature as a result. When the synchronous motor is supplied with independently excited multi-phase AC electromagnets on both the rotor and the stator, it is termed as a doubly-fed machine. The most widely used AC-type motors are the synchronous AC motor and the induction AC motors.

Question

A 6 kV , 1000 kVA , 3-ph alternator is
delivering full-load at 0.8 lagging. Its reactance is
20% and resistance negligible. By changing the
excitation, the e.m.f. is increased by 25% at this
load. Calculate the new current and power factor.
The machine is connected to infinite bus-bars.

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