Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Chapter 39, Problem 14SQ
Induction motors and welding transformers require magnetizing current, which causes
- a. lagging power factor.
- b. leading power factor.
- c. unity power factor.
- d. zero power factor.
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Choose True (V) or false( x) for the following :
4) Reluctance is a measure of "opposition" the magnetic circuit offers to the flux.
5) The rated output power (transformer rating) can be used to determine the turns ratio of
the transformer.
6) With the increase in speed of a series DC motor, Both back emf as well as line current
increase.
7) When an induction motor is stationary, the stator and rotor windings form the equivalent
of a transformer.
8) Increasing the load current for DC Self-excited generator Shunt-Wound Generator will
increase the terminal voltage.
9) In lap windings there are as many paths in parallel and used to produce high current, low
voltage output.
10) In 3-pahse induction motor, if the rotor speed increases, the rate at which the rotating
magnetic field cuts the rotor bars is increasing.
Why is it necessary to conduct polarity tests on transformers?
B) fill in the blanks:
that of rotor MMF.
1)In a 3-phase synchronous motor the speed of stator MMF is .........
2)The synchronous reactance of the synchronous machine is.......
3) When two transformers are operating in parallel, they will share the load as under......
4)A synchronous motor is operating on no-load at unity power factor. If the field
current is increased, power factor will become..
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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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, electrical-engineering and related others by exploring similar questions and additional content below.Similar questions
- (3) The speed of the synchronous motor: a- Reduced linearly with the increase of load. b- Reduced in a non-linear manner with the increase of load. c- Remains the same with increase of load. (4) The flux density inside the transformer core: a- Reduced with the increase of load. b- Increased with the increase of load. c- Is constant with the increase of load.arrow_forwardA thicker wire is used in the DC series field winding than DC shunt field winding in DC machines. * O because it carries the load current. O to prevent mechanical vibrations. O to provide strength. O to produce large flux. The speed of a DC motor can be changed by varying - armature resistance circuit O flux per pole O voltage source O all of abovearrow_forwardFill in the following blanks:1. Lap winding is suitable for ……. Voltage, …… current d.c. generators.2. The critical resistance of the d.c. generator is the resistance of ……. .arrow_forward
- In alternator armature winding why we prefer : a- short pitch winding w.r.t. full pitch winding? b- distributed winding w.r.t. concentrated winding? c- double layer winding w.r.t. single layer winding?arrow_forwardConsider the following statements regarding the design of the distributed armature winding in a three-phasealternator:1. It reduces the phase belt harmonics.2. It increases utilization of armature iron and copper.3. It increases rigidity and mechanical strength of the winding.4. It reduces copper in the overhand of the winding. Which of the statements are correct? a. 1,3 and 4b. 2,3 and 4c. 1,2 and 3d. 1,2,3 and 4arrow_forwardThe shunt field winding of a shunt generator has a resistance of 80 ohms at 20⁰C. After several hours of continuous operation, the winding temperature rises to 50⁰C. How much is the winding resistance under this condition, Assume the resistance temperature coefficient of copper to be 0.004 ohm per degree at 0⁰C.arrow_forward
- What are the conditions in paralleling of these DC Generators:a. Shuntb. Seriesc. Compoundarrow_forwardWhy the rotary transformers suffer from low efficiency?arrow_forwardA short shunt compound DC generator supplies a load of 10A at a voltage of 10 volts. If the resistances of Armature, shunt field and series field windings are 0.01 ohm, 1 ohm and 0.00 ohm respectively. c) write down the factors to improve the generated voltage. Generated Voltage is 10.2 Varrow_forward
- 1.Two identical shunt generators running in parallel, each with armature resistance of 0.02 ohms and field resistance of 50 ohms. The combined load current is 5000A. The field are so excited that the generated voltages of one machine is 610V and the other is 600V. The terminal voltage of this parallel combination will be. www Ish1 Rh1 a.350-360 V b.450-460 V c. 550-560V Rat www az G₂ Raz 5000 A Ish2arrow_forwardQ3/ A/ Compare between de series and shunt generator. Q3/ B/ Briefly explain the commutating process in dc machine.arrow_forwardDEGREE: ELECTRICAL ENGINEERING SUBJECT/COURSE: AC MACHINES Answer the following questions (A, B and C) depending on the topic. 1. ALTERNATORS A. Why is it necessary to maintain the speed of an alternator at all times and how do they control the speed of an alternator when in operation? B. Distinguish between half-coiled and full-coiled armature windings in alternators. C. Why are fractional pitch windings generally used in alternators?arrow_forward
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How Electric Motors Work - 3 phase AC induction motors ac motor; Author: The Engineering Mindset;https://www.youtube.com/watch?v=59HBoIXzX_c;License: Standard Youtube License