24. NEMA-rated general-purpose motors can operate on voltages 610% of their rated nameplate voltage. An unbalanced voltage situation is extremely damaging to a motor. Calculate the expected heat rise in a motor subjected to an unbalanced voltage situation where the voltages between phases AB = 465 volts, BC = 487 volts, and CA = 473 volts. Add these voltages: Total Find the average voltage: Total ÷ 3 = volts Full Subtract the average voltage from the voltage reading that results in the greatest difference: volts 100 ÷ Greatest voltage difference/Average voltage = %voltage unbalance Temperature rise in the winding with highest current = 2 × (percent voltage unbalance)? % temperature rise in the winding with highest current

24. NEMA-rated general-purpose motors can operate on voltages 610% of their rated nameplate voltage. An unbalanced voltage situation is extremely damaging to a motor. Calculate the expected heat rise in a motor subjected to an unbalanced voltage situation where the voltages between phases AB = 465 volts, BC = 487 volts, and CA = 473 volts. Add these voltages: Total Find the average voltage: Total ÷ 3 = volts Full Subtract the average voltage from the voltage reading that results in the greatest difference: volts 100 ÷ Greatest voltage difference/Average voltage = %voltage unbalance Temperature rise in the winding with highest current = 2 × (percent voltage unbalance)? % temperature rise in the winding with highest current

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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A 2 pole, 3 phase, 50 Hz induction motor is running on no load with the slip 4%. Calculate (i) the synchronous speed, (ii) speed of the motor.
b) A three-phase 4-pole 208 V, 60 Hz induction motor with Y-connected stator has the following set of parameters per phase: stator resistance R₁ = 0.22 S2, stator leakage reactance X₁ = 0.43 2, rotor equivalent resistance R₂ = 0.1272, rotor leakage reactance X₂= 0.43 2, and magnetising reactance XM= 15 2. For a slip of 0.05, calculate the following: i. 11. iii. Stator line current; Stator copper losses and the air-gap power; Output mechanical power.
a 4-pole, 415V/60Hz three-phase squirrel-cage induction motor is Y-connected and has a rated speed of 1470rpm and R =0.282, R'2= 0.210, X1=X'2= 0.420, Xm= 55N. 1. If the motor is operated at speed of 2058rpm and Volt-per-Hertz control is used: 1. What would be the voltage? 2. What would be the frequency of the supply? (in Hz) 3. In this case, the motor is operating in what region? a. Constant speed b. Constant Power Oc. Constant power and torque d. Constant Torque Oe. Cannot be specified. More information is needed 2. If Volt-per-Hertz control is used and the voltage is 375, find: 1. what should be the frequency? (in Hz) 2. What is the maximum torque in this case?
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1. In the case of an 8-pole induction motor, the supply frequency was 50-Hz and the shaft speed was 735 r.p.m. What were the magnitudes of the following: (1) synchronous speed (ii) (iii) per unit slip (iv) speed of slip percentage slip
A 380 V, 50 Hz, 6-pole, 960 rpm, star connected induction motor has the following parameters: stator and rotor resistances are 1.25 each, and stator and rotor leakage reactance are 1.5 each (magnetising reactance can be neglected). The motor is controlled by simultaneous stator voltage and frequency variation. Voltage boost is not used and the motor is controlled using V/f constant law. The motor is supplied from a three-phase voltage source inverter. The motor operates at 30 Hz. Calculate the ratio of the maximum torque at this frequency with respect to the one at rated frequency, for both motoring and generation. b) For the same 30 Hz operating frequency, calculate ratio of the starting current at this frequency with respec to the starting current at rated frequency. c) Assume that the voltage boost of 20 V (phase voltage) is used. Calculate new value of the phase voltage that would be applied in this case for the operating frequency of 30 Hz. Repeat part b) with this new voltage…
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13. A synchronous machine is run as an unloaded motor. If a low voltage is supplied at the ratedfrequency, and if the full-load armature current flows, a test is being run to determine theA. windage loss.B. I²R loss.C. stray-load loss.D. core loss. Note: I have doubts if it is the letter A or the letter B, can you help me in this question, thanks.
15. What are the following statements are true for DC Motor? I. Motor converts Electrical Energy to Mechanical Energy II. Motor supply current to the armature winding III. Back EMF is lesser than the Supply voltage IV. Fleming's Right-hand rule a. I and II b. II and IV c. I,II and III d. I,II and IV