Electricity and Magnetism

The Power Balance of an Induction Motor The total (apparent) power of an induction motor is S = P1 + jQl = 3V1I1 cos φ1 + j3V1I1 sin φ1 where P1 is its active power and Q1 is it reactive power. The active power P1 defines the average power associated with the irrever­sible conversion of […]
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Under running conditions, the frequency of the current in the stator circuit is f and that of the current in the rotor circuit is f 2 = f s is, so no common phasor diagram may be constructed for the two circuits. However such a phasor diagram may be plotted if we assume an equivalent […]
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The Equivalent Circuit for a Phase of an Induction Motor In calculating the process taking place in an induction motor, resort is usually made to the equivalent circuit of one phase. This circuit is assumed to include fixed resistive and inductive elements and also a variable resistive element to represent the mechanical load applied to […]
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The Equation of Electric State for a Rotor Phase of an Induction Motor The revolving magnetic field induces in a rotor phase an emf, e2, at frequency f2 = P (nl – n)/60. We can express this frequency in terms of the supply-line frequency on dividing and multiplying the right-hand side of this expression by […]
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The Equation of State for a Stator Phase of an Induction Motor The emf induced in each turn of the stator winding by the revol­ving magnetic field, is, in accord with Eq. (2.2), given by eturn = – dΨ/dt Since it is legitimate to assume that the normal component of the magnetic induction is distributed […]
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The Revolving Rotor Field and the Working Revolving Field in an Induction Motor To begin with, let us assume that the rotor circuit is open so that there is no current flowing in it, no electromagnetic forces are acting on the rotor, and it is at rest. Then the magnetic field in the machine will […]
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The Modes of Operation of a Three-Phase Induction Machine The mode of operation for a three-phase induction machine de­pends on the interaction between the currents in the stator and rotor windings. The interaction of the revolving magnetic field produced by the currents in the stator winding with the currents in the rotor winding causes the […]
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The Revolving Magnetic Field of the Stator When three-phase voltages are applied to the stator-winding ter­minals, balanced three-phase currents flow in the phase windings and a rotating magnetic field is produced in the air gap of the machi­ne. This field induces an emf in the rotor winding shorted together or connected in series with a […]
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Induction Machines Of the many types and forms of present-day electric machines those most commonly used are induction machines. ordinarily employed a motors. An induction machine is all a.c. two-winding unit in which only one (usually the stator) winding is supplied with an alternating cur­rent at a constant frequency from an external source, while in […]
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Instrument Transformers These may be current transformers and voltage transformers. They are used, firstly, for the purpose of changing currents or volt­ages in a power circuit to values which render them convenient for measurement, and secondly in order to extend the range of the asso­ciated instruments. Voltage instrument transformers are used in conjunction with volt­meters, […]
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