DC GENERATOR THEORYDC GeneratorsFigure 3 Basic Operation of a DC GeneratorA single conductor, shaped in the form of a loop, is positioned between the magnetic poles. Aslong as the loop is stationary, the magnetic field has no effect (no relative motion). If we rotatethe loop, the loop cuts through the magnetic field, and an EMF (voltage) is induced into the loop.When we have relative motion between a magnetic field and a conductor in that magnetic field,and the direction of rotation is such that the conductor cuts the lines of flux, an EMF is inducedinto the conductor. The magnitude of the induced EMF depends on the field strength and therate at which the flux lines are cut, as given in equation (5-1). The stronger the field or the moreflux lines cut for a given period of time, the larger the induced EMF.Eg = KFN (5-1)whereEg = generated voltageK = fixed constantF = magnetic flux strengthN = speed in RPMThe direction of the induced current flow can be determined using the "left-hand rule" forgenerators. This rule states that if you point the index finger of your left hand in the directionof the magnetic field (from North to South) and point the thumb in the direction of motion ofthe conductor, the middle finger will point in the direction of current flow (Figure 4). In thegenerator shown in Figure 4, for example, the conductor closest to the N pole is traveling upwardacross the field; therefore, the current flow is to the right, lower corner. Applying the left-handrule to both sides of the loop will show that current flows in a counter-clockwise direction in theloop.ES-05 Page 6 Rev. 0
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