Ideal-transformer-summary-figure

Ideal-transformer-summary-figure - Summary: Irrespective of...

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Unformatted text preview: Summary: Irrespective of several practical effects, transformers are simplest devices. A tranformer simply consists of several coils coupled by a magnetic path. Electrically all coils are physically uncoupled. Many transformers have efficiency exceeding 98%. Some transformers even have efficiency in the order of 99.9%. Two basic principles guide the behavior of an ideal transformer: • Voltage induced per turn is the same in any coil. • The mmf of primary coil has to balance the mmfs of all other coils. In the case of two coils denoted by p (primary) and s (secondary) with turns Np and Ns , we have Vp Np = and Ip Np = Is Ns . Vs Ns In the case of three coils denoted by p (primary), s (secondary), and t (tertiary) with turns Np , Ns , and Nt , we have Vp Np Vp Np = , = , and Ip Np = Is Ns + It Nt . Vs Ns Vt Nt The above guiding principles lead to impedance transformation. That is, a coil feeding an impedance can equivalently be thought of as primary coil feeding another impedance called reflected impedance. In the case of two coils denoted by p and s, the secondary impedance Zs is reflected as primary impedance Zp , Np 2 Zs . Ns If the primary coil is supplying more than one coil, each such coil reflects an impedance into the primary. All such reflected impedances are in parallel. Zp = Practical Effects: • A current called excitation current is necessary to magnetize the medium. The excitation current is often not sinusoidal, it contains several harmonic frequencies. There are two kinds of excitation losses, hysteresis loss and eddy current loss. These losses together are known as core losses or iron losses. • Not all the flux generated by one winding links the other windings. This leads to leakage reactances. • Every coil has a resistance, and it leads to what are known as copper losses. ...
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