Electrical Transformers and Rotating Machines
4th Edition
ISBN: 9781305494817
Author: Stephen L. Herman
Publisher: Cengage Learning
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Textbook Question
Chapter 1, Problem 4RQ
How can the polarity of an electromagnet be determined if the direction of current flow is known?
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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)
Thermal conductivity measurement for good conductors using Searle's Method
The working current has a power of 100 kW and a power factor of 0.50. After a capacitor of 75 KVAR is installed, what does the
power factor become?
A 0.84
B 0.71
C 0.63
D 0.78
E 0.92
Chapter 1 Solutions
Electrical Transformers and Rotating Machines
Ch. 1 - Is the north magnetic pole of the earth a north...Ch. 1 - What were early natural magnets known as?
Ch. 1 - The south pole of one magnet is brought close to...Ch. 1 - How can the polarity of an electromagnet be...Ch. 1 - Define the following terms:
Flux...Ch. 1 - A force of 1 ounce is equal to how many dynes?
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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
- Assume that a primary current of 75 amperes flows through the windings of the transformer in question 4. How much current will flow in the secondary winding?arrow_forwardA CT has a current flow of 80 amperes in its primary winding and a current of 2 amperes in its secondary winding. What is the ratio of the CT?arrow_forwardTrue or False? The strength of the magnetic field in an electromagnet increases with an increase in the number of turns of wire and the current flowing through them.arrow_forward
- If the secondary of the transformer in question 5 supplies a current of 9.6 amperes to a load, what is the primary current? (Disregard excitation current.)arrow_forwardHow much current will flow in the primary of the transformer in question 4?arrow_forwardA current transformer has 4 turns of wire in its primary winding. How many turns of wire are needed in the secondary winding to produce a current of 2 amperes when a current of 60 amperes flows in the primary winding?arrow_forward
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