The situation is further complicated by energy losses within the iron core. The effects of hysteresis and eddy currents conspire to further distort and complicate the current waveform, making it even less sinusoidal and altering its phase to be lagging slightly less than 90 o behind the applied voltage waveform. This coil current resulting from the sum total of all magnetic effects in the core (dΦ/dt magnetization plus hysteresis losses, eddy current losses, etc.) is called the exciting current . The distortion of an iron-core inductor’s exciting current may be minimized if it is designed for and operated at very low flux densities. Generally speaking, this requires a core with large cross-sectional area, which tends to make the inductor bulky and expensive. For the sake of simplicity, though, we’ll assume that our example core is far from saturation and free from all losses, resulting in a perfectly sinusoidal exciting current. As we’ve seen already in the inductors chapter, having a current waveform 90 o out of phase with the voltage waveform creates a condition where power is alternately absorbed and returned to the circuit by the inductor. If the inductor is perfect (no wire resistance, no magnetic core losses, etc.), it will dissipate zero power. Let us now consider the same inductor device, except this time with a second coil wrapped around the same iron core. The first coil will be labeled the primary coil, while the second will be labeled the secondary : wire coil iron core wire coil If this secondary coil experiences the same magnetic flux change as the primary (which it should, assuming perfect containment of the magnetic flux through the common core), and has the same number of turns around the core, a voltage of equal magnitude and phase to the applied voltage will be induced along its length. In the following graph, the induced voltage waveform is drawn slightly smaller than the source voltage waveform simply to distinguish one from the other: 313
Φ = magnetic flux Φ e p = primary coil voltage e s = secondary coil voltage e p e s i p = primary coil current i p 314
Chapter 16 Electronics ( NOTE TO SELF: Mark: I have very little idea of how to make this flow, fit in or even how best to explain any of it. All the content in here is just trawled from other GFDL projects: The syllabus document has NO meaningful information on this stuff. ) Electronics: 16.1 capacitive and inductive circuits 16.1.1 A capacitor ( NOTE TO SELF: If we are going to talk of capacitive circuits we need a definition of capacitor. ) A capacitor (historically known as a ”condenser”) is a device that stores energy in an electric field, by accumulating an internal imbalance of electric charge. It is made of two conductors separated by a dielectric (insulator). The problem of two parallel plates with a uniform electric field between them is a capacitor.
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