Engineering Talks

# DrD

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1. ## What is power factor?

Power factor is the cosine of the angle between the voltage and the current. It is the third factor in the product that expresses the power, P = V*I*cos(phi) where phi is the phase angle. DrD
2. ## What are real, reactive, and apparent power?

Real power is just what it says, power as in work done per unit of time. In electrical systems, the real power is calculated as Preal = V*I*cos(phi) where V = voltage I = current phi = phase angle between current and voltage Reactive power is Preact = V*I*sin(phi) I've never heard the term "apparent power" but I suspect what you mean is what I know as Volt-Amperes = V*I The real power is the in-phase part of the volt-ampere product while the reactive power is the out-of-phase part of that product. DrD
3. ## Why are all cores exposed to ac flux variations laminated?

Ths is done to reduce eddy current losses by preventing current flow perpendicular to the laminations. The laminates are electrically insulated from each other (usually by varnish) which blocks current flow while allowing magnetic flux to flow freely. DrD
4. ## Just how does a decrease in flux produce an increase in speed in a linear machine?

This process is called "field weakening" and it was used for speed control on the ancient rolling mill where I worked long ago. As the field current is reduced, flux must be cut more rapidly to maintain the back EMF. The only way this can happen is for the rotor to turn more rapidly, thereby cutting more flux per unit of time. DrD The term "linear machine" seems ambiguous to me. I think you intend to describe an electrical machine (motor) described by linear differential equations. The term can also be used to describe an electric motor for which the moving element translates rather than rotates. For a translating induction machine, the usual acronym is LIM, Linear Induction Machine. Such machines can also be built in synchronous form, known as LSM, Linear Synchronous Machines. The linear machines of this sort are being used to launch aircraft from aircraft carriers. DrD
5. ## Mechanics of Machines, 2nd ed - free textbook

I hope that a great many folks will download this file. It is better than that previously posted, and probably my last effort. It is not yet available at Lulu.com, but I hope to eventually make that happen. It seems inappropriate to rate my own book, but it is required by the website. DrD
6. ## What is Ampere's law?

Now that is an interesting question! Do you mean Ampere's circuital law? or Do you mean Ampere's force law?
7. ## The linear machine in Figure 1-19 is running at steady state. What would happen to the bar if the voltage in the battery were increased?

Where is Fig 1-19? How can anyone answer with such a poorly stated question? DrD
8. ## Mechanics of Machines, 2nd ed - free textbook

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