8. A4-pole, 50-Hz, 3-phase induction motor has a slip-ring rotor with a resistance and standstill reactanceof 0.04 2 and 0.2 Q per phase respectively. Find the amount of resistance to be inserted in each rotorphase to obtain full-load torque at starting. What will be the approximate power factor in the rotor atthis instant ? The slip at full-load is 3 per cent.[0.084 2, 0.516 p.f.] (London University)9. A 3-0 induction motor has a synchronous speed of 250 r.p.m. and 4 per cent slip at full-load. Therotor has a resistance of 0.02 Q/phase and a standstill leakage reactance of 0.15 Q/phase. Calculate(a) the ratio of maximum and full-load torque (b) the speed at which the maximum torque is devel-oped. Neglect resistance and leakage of the stator winding.[(a) 1.82 (b) 217 r.p.m.] (London University)10

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8. A4-pole, 50-Hz, 3-phase induction motor has a slip-ring rotor with a resistance and standstill reactance of 0.04 Q and 0.2 Q per phase respectively. Find the amount of resistance to be inserted in each rotor phase to obtain full-load torque at starting. What will be the approximate power factor in the rotor at this instant ? The slip at full-load is 3 per cent. [0.084 2, 0.516 p.f.] (London University)

8. A4-pole, 50-Hz, 3-phase induction motor has a slip-ring rotor with a resistance and standstill reactance of 0.04 Q and 0.2 Q per phase respectively. Find the amount of resistance to be inserted in each rotor phase to obtain full-load torque at starting. What will be the approximate power factor in the rotor at this instant ? The slip at full-load is 3 per cent. [0.084 2, 0.516 p.f.] (London University)

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 three-phase induction motor, operating at rated voltage and frequency, has a startingtorque of 1.35 times and a maximum torque of 2.2 times, both with respect to its rated-loadtorque. Ignoring the effects of the stator resistance and rotational losses and assumingconstant rotor resistance, determine the slip rated load, and the rotor current at starting (as a percentage of the rotor current at rated load). The slip at maximum torque is 0.343 if that helps.
A three-phase induction motor, at rated voltageand frequency, has a starting torque of 140 percentand a maximum torque of 210 percent of full-loadtorque. Neglect stator resistance and rotational lossesand assume constant rotor resistance. Determinea. The slip at full load.b. The slip at maximum torque.c. The rotor current at starting as a percentage offull-load rotor current.
A three-phase induction motor, operating at rated voltage and frequency, has a startingtorque of 1.35 times and a maximum torque of 2.2 times, both with respect to its rated-loadtorque. Ignoring the effects of the stator resistance and rotational losses and assumingconstant rotor resistance, determine the slip at the maximum torque;
a. A three-phase, 220-V, 60-Hz induction motor runsat 1,140 r/min. Determine the number of poles (forminimum slip), the slip, and the frequency of therotor currents.b. To reduce the starting current, a three-phasesquirrel cage induction motor is started byreducing the line voltage to Vs/2. By what factorare the starting torque and the starting currentreduced?
The rotor resistance and reactance per phase of a 4-pole, 50-Hz, 3-phase induction motor are 0.025 ohm and 0.12 ohm respectively. Make simplifying assumptions, state them and : (i) find speed at maximum torque (ii) find value of additional rotor resistance per phase required to give three-fourth of maximum torque at starting. Draw the equivalent circuit of a single-phase induction motor.
Q/ A 3-phase squirrel-cage induction motor, at rated voltage and frequency, has a maximum torque of 225 percent and starting torque of 150 percent of full-load torque. Neglect stator resistance and rotational losses and assume costant rotor resistance. Calculate:i) the slip at maximum torque.ii) the slip at full load.
A 4-pole, 50 hz, 3-phase induction motor has a slip-ring rotor with resistance and standstill reactance of 0.04 ohm and 0.2 ohm per phase respectively. Find the amount of resistance to be inserted in each rotor phase to obtain full-load torque at starting. What will be the approximate power factor in the rotor at this instant? The slip at full-load is 3 percent.
A 80 kW, 480-V, 60-Hz, six pole induction motor has a slip of 5 percent when operating at fullload conditions. At full-load conditions, the friction and windage losses are 300 W, and the core losses are 400 W. For full-load conditions, compute the induced torque,T-ind, in N-m.
A three phase, 50Hz, 6-pole squirrel cage induction motor runs at 960-rpm on full load. The stand still rotor resistance and reactance per phase are 0.01 ohm and 0.05 ohm respectively. Express the maximum torque developed in terms of full load toque. Find the slip at which the maximum torque occurs.
A 3300-V, 50-Hz, 3-phase, 4-pole, star-connected induction motor has identical primary and referred secondary impedances of value 3 + j9 ohm per phase. The turns-ratio per phase is 3/I (stator/rotor), and the rotor winding is connected in delta and brought out to slip rings. Calculate: the full-load torque at rated slip of 5%; the maximum torque at normal voltage and frequency; the supply voltage reduction which can be withstood without the motor stalling; the maximum torque if the supply voltage and frequency both fall to half normal value; the increase in rotor-circuit resistance which, at normal voltage and frequency, will permit maximum torque to be developed at starting. Express this: as a fraction of normal R2and as (3) ohmic values to be placed in series with each of the slip-ring terminals and star connected.
A 6-pole, 60-Hz, Y-connected, three-phase induction motor develops a torque (Td) of 250 N.m at a speed of 720 rpm. The rotor resistance is 0.4 Ohm/phase, and the stator winding impedance is negligible. A) What is the air-gap power? B) What is the rotor current refered to the stator? C) If the rotational loss is 1kW, what is the motor output power in hp?
A 6-pole, 50 Hz, 3-phase induction motor runs at 960 rpm while delivering a shaft torque of 120 N-m. If friction and windage loss amount to 180 W., determine the rotor copper loss.