A three-phase, six-pole, squirrel-cage induction motor is to be controlled by terminal voltage variation using pairs of inverse-parallel thyristors in the supply lines with symmetrical phase-angle triggering. The motor is rated at 50 kW, 240 V, 50 Hz. If it operates at a full-load efficiency of 0.9 p.u. and power factor 0.85. Calculate the rms current rating and maximum voltage rating required of the thyristors. The motor drives a fan load characterised by the relation T, = kw?, where T, the shaft torque is and w is the motor speed. Operation is required to give full load at full speed; which corresponds to 5 % slip, and at three quarters of the full speed. What approximate reduction of motor power is required (compared with full-load, full-speed operation) in order to realise operation at 750 rpm? If the motor operates at full voltage at upper speed, calculate, approx- imately, the voltage required at the lower speed. Explain and estimate the change of thyristor firing-angle necessary to obtain the required change of voltage.

A three-phase, six-pole, squirrel-cage induction motor is to be controlled by terminal voltage variation using pairs of inverse-parallel thyristors in the supply lines with symmetrical phase-angle triggering. The motor is rated at 50 kW, 240 V, 50 Hz. If it operates at a full-load efficiency of 0.9 p.u. and power factor 0.85. Calculate the rms current rating and maximum voltage rating required of the thyristors. The motor drives a fan load characterised by the relation T, = kw?, where T, the shaft torque is and w is the motor speed. Operation is required to give full load at full speed; which corresponds to 5 % slip, and at three quarters of the full speed. What approximate reduction of motor power is required (compared with full-load, full-speed operation) in order to realise operation at 750 rpm? If the motor operates at full voltage at upper speed, calculate, approx- imately, the voltage required at the lower speed. Explain and estimate the change of thyristor firing-angle necessary to obtain the required change of voltage.

Introductory Circuit Analysis (13th Edition)

13th Edition

ISBN:9780133923605

Author:Robert L. Boylestad

Publisher:Robert L. Boylestad

Chapter1: Introduction

Section: Chapter Questions

Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...

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