Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Textbook Question
Chapter 39, Problem 15SQ
A synchronous motor can be used to increase the power factor of an electrical system by
- a. reducing the speed.
- b. overexciting the stator field.
- c. operating at unity power factor.
- d. applying DC to the stator field.
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Which of the following statements about three-phase induction motor is false
(A) The speed of rotation of the magnetic field is called the synchronous speed.
(B) A three-phase supply connected to the rator produces a rotation magnetic field.
(C)The rotating magnetic field has a constant speed and constant magnitude.
(D) It is essentially a constant speed type machine.
1.5 A 10‐pole, 380 ‐V, 50 Hz, D‐connected three‐phase induction motor is rotating a quarry belt conveyor. The machine has the following parameters, referred to the stator, on a per phase basis:
Stator Parameters
Winding Resistance................0.19 Ω .........
Winding Reactance.................1.12 Ω..........
Rotor Parameters
Winding Resistance......................0.29 Ω
Winding Reactance.....................1.12 Ω
Magnetising Reactance................................16.8 Ω
Equivalent Core‐loss Resistance....................900 Ω.
The friction and windage losses are 320 W. When the motor runs at its rated slip of 2.6 %. Determine:
1.5.1 The stator current.
1.5.2 Estimate the Output torque of the motor under the rated conditions.
1.5.3 The Motor…
Chapter 39 Solutions
Electric Motor Control
Ch. 39 - Prob. 1SQCh. 39 - What is the effect of the starting winding of the...Ch. 39 - What are typical applications of synchronous...Ch. 39 - Prob. 4SQCh. 39 - A loaded synchronous motor cannot operate...Ch. 39 - Why must a discharge resistor be connected in the...Ch. 39 - Depending on their power factor ratings, what is...Ch. 39 - At what power factor do incandescent lights...Ch. 39 - Prob. 9SQCh. 39 - The speed of a synchronous motor is fixed by the...
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- K-1)The speed of a 3-phase wound-rotor induction motor can be changed by varying the amount of resistance in the rotor circuit. a) true b) false K-2). Which of the following statements are true about a 3-phase synchronous motor? a) It is a constant speed motor even under varying loads. b) It runs at the same speed the magnetic field rotates on the stator. c) It can correct its own, and the supply line's power factor d) all of the above K-3. A) What determines the speed of a 3-phase synchronous motor? a) the number of poles b) the frequency of the supply c) both "a" and "b" d) neither "a" nor "b" K-3)B) From a technician's standpoint, which of the following is the most practical method of providing a wide range of speed control for a 3-phase synchronous motor? a) by changing the frequency b) by changing the number of poles c) both "a" and "b" d) neither "a" nor "b"arrow_forwardA DC generator has terminal voltage of 250 V and an induced voltage of 262 V when the generator is loaded. The brush drop is 1 volt per brush and the armature resistance is 0.03 ohm and the shunt field circuit resistance is 35 ohms. Neglected armature reaction and determine the following: (1) The load current. (2) The power of the load in kW. (3) The % voltage regulation.arrow_forward2. A 2-pole, 50 Hz induction motor supplies 15 kW to a load at a speed of 2950 rpm. a. What is the motor's slip? b. What is the induced torque in the motor in N-m under these conditions? c. What will be the operating speed of the motor be if its torque is doubled? d. How much power will be supplied by the motor when the torque is doubled?arrow_forward
- As shown in the figure below, this is a speed regulation method for DC separately excited motor. a) What is the speed regulation method? b) What are the characteristics for this speed regulation method? no ne 11₂ 2 11₂ I I D E Ra R₂ Rs 1 3arrow_forwardDEGREE: ELECTRICAL ENGINEERING SUBJECT/COURSE: AC MACHINES Answer the following questions based on its topic. 5. SYNCHRONOUS MOTORS A. What is necessary to start a synchronous motor to rotate from standstill? Describe the process. B. What is meant by synchronous condenser? C. Why is it possible for synchronous motors be used as a power factor correction device and what applications do synchronous motors commonly used? Describe the operation.arrow_forwardL-1). The 3-phase wound-rotor induction motor has .... . a) high starting torque b) low starting current c) both "a" and "b" d) neither "a" nor "b" L-2). The 3-phase wound-rotor induction.........a) motor has a wire wound rotor b) motor's rotor can be connected to an external resistive load by way of slip rings and brushes c) motor requires more maintenance than the 3-phase squirrel-cage induction motor d) all of the above L-3). The 3-phase wound-rotor induction motor's rotor circuit's resistance should be adjusted so it is__________ during starting. a) low b) high c) either "a" or "b" d) neither "a" nor "b" L-4). Will a 3-phase wound-rotor induction motor start with no external circuit connected to its rotor leads? a) yes b) noarrow_forward
- d) A 2-pole induction motor is fed with a 230 V, 50 Hz supply and is running at no load. i. Calculate its angular speed in rpm. ii. Explain how can we slow down the speed of the motor above, at no load? iii. Explain what will happen to the speed of the motor if we slowly add amechanical load to the motor.arrow_forwardAn induction motor with a power rating of 37.5 kW, 4 poles operates at 50 Hz supply frequency. It has friction loss of 3320 W and which is equal to Windage losses. When the motor runs at 1440 rpm it is expected to deliver full load output. With the above details determine the following: a) Synchronous speed b) Mechanical power developed by the motor c) rotor copper loss d)arrow_forwardA DC series motor having a resistance of 0.4 o and runs at 2000 rpm when connected to 250 V supply and drawing a current of 2O A. (i) What resistance must be added in order to limit the speed to 4000 rpm when armature current is 5A? Assume flux varies linearly. (ii) What resistance must be added to limit the speed to 1000 rpm when armature current is 30 A? Assume that the flux at 30 A is 20% more than that at 20A. (iii) At what speed the motor will run if it is connected directly to 250 V supply when the load is such that the current drawn is 30 A? *arrow_forward
- lap to induce the same voltage if it is wave wound? (Ans. 500 V; 375 rpm) Q 5. A wave-wound armature of a 6-pole generator has 51 slots. Each slot contains 20 conducto voltage required to be generated is 250 V. What would be the speed of coupled prime mover if pole is 0.07 Wb. If the armature is rewound as lap-wound machine and run by same prime move will be the generated voltage? (Ans. 70 rpm; 83.3 V)arrow_forwardThe rotor resistance and standstill reactance of a 3-phase induction motor are 0.015 Q and reactance 0.09 0 per phase. (i) What is the p.f. of the motor at start? (ii) What is the p.f. at a slip of 4 per cent? (iii) If the number of poles is 4, the supply frequency is 50-Hz and the standstill e.m.f. per rotor phase is 110 V, find out the full-load torque. Take the full-load slip as 4 per cent.arrow_forwardQ. Excited DC motor.arrow_forward
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Working of Synchronous Motor; Author: Lesics;https://www.youtube.com/watch?v=Vk2jDXxZIhs;License: Standard Youtube License