Electrical Transformers and Rotating Machines
4th Edition
ISBN: 9781305494817
Author: Stephen L. Herman
Publisher: Cengage Learning
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Textbook Question
Chapter 21, Problem 11RQ
The short-circuit protective device supplying the motors in question #10 is an inverse-time circuit breaker. What size circuit breaker should be used?
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Question 2 Calculate the amount of DC current required for the magnetic circuit given below to generate a
flux density of 1.0 T in the airgap. The details are
Number of turns, N = 400
The core is made up of steel, the B-H characteristic has been given below
The magnetic core length, le = 500 mm
The airgap length, Ig = 2 mm
The cross-sectional area of the core, Ag = 100 mm²
Neglect leakage and fringing.
Core
Cross-sectional
i(1)
area
as
Air gap
Magnetic path
length
Figure 1
2.0
1.8
B-H Curves for Various Metals
Steel
1.6
1.4
Magnetic
Saturation
1.2
1.0
0.8
Iron
근 0.4
Air
0.2
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Magnetic Field Strength - H (A/m)
Figure 2
Flux Density - B (T)
What happens when the low-voltage current flow in the coil primary winding is interrupted by the switching device?
The primary winding delivers a high-voltage spark to the plugs.
The magnetic field in the coil primary builds.
The secondary voltage drops to zero volts.
High voltage is induced in the secondary windin
You are Working as a plant electrician. You were told that a large DC motor was returned from the rewind shop and was installed on the previous shift. The motor seem to operate properly until the load was added. The motor then stopped, reversed direction, and begun to run at high speed. What is the probable cause of the trouble, and what would you do to correct the problem? Explain your answer.
Chapter 21 Solutions
Electrical Transformers and Rotating Machines
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, mechanical-engineering and related others by exploring similar questions and additional content below.Similar questions
- An open winding in an electric motor means that A. the winding is making contact with the motor frame. B. one winding is making contact with another winding. C. a wire in one winding is broken. D. the centrifugal switch to the start winding is open.arrow_forwardWhat are the three types of armature windings?arrow_forwardIs the resistance in the start winding greater or less than the resistance in the run winding?arrow_forward
- What type of field winding is made with many turns of small wire?arrow_forwardA 10 kVA transformer has a primary voltage of 208 volts and a secondary voltage of 120 volts. What size circuit breaker should be used to protect the primary winding?arrow_forwardThe secondary of the transformer in question #3 has a rated voltage of 2400 volts. What size fuse should be used to provide branch circuit protection?arrow_forward
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