. A text-book of electrical engineering;. Fig. 233 resultant EC. The student should check both these examples by drawingthe vectors from the origin and completing the parallelogram. Kirchhoffs second rule for any closed circuit can now be expressed asfollows: The vector sum of the electromotive forces is equal to the vectorsum of the products IR. Thisproduct has the same phase as thecurrent. In Fig. 235 the vectorOA represents the electromotiveforce induced in the armature ofan alternating current generatorby the magnetic field of the polesystem, the vector I represents thecurrent flowing thro
. A text-book of electrical engineering;. Fig. 233 resultant EC. The student should check both these examples by drawingthe vectors from the origin and completing the parallelogram. Kirchhoffs second rule for any closed circuit can now be expressed asfollows: The vector sum of the electromotive forces is equal to the vectorsum of the products IR. Thisproduct has the same phase as thecurrent. In Fig. 235 the vectorOA represents the electromotiveforce induced in the armature ofan alternating current generatorby the magnetic field of the polesystem, the vector I represents thecurrent flowing through the arma-ture and round the external circuit;this current is assumed to lag 45°behind OA. OB represents theelectromotive force induced in thearmature by the flux produced by the current I flowing through thearmature winding; as will be shown in the following section, this 90 degrees behind the current, as seen in Fig. 235. OD represents the 16—2. Fig- 235 244 Electrical Engineering resultant induced in the armature. This will be used up tosome extent i» overcoming the internal resistance of the armature; theproduct IRa will be in phase with the current and is shown in Fig. 235 asthe vector OC or ED. The other component of OD, viz. OE, representsthe terminal of the generator. Fig. 236 is the same construction but without the parallelograms. Theelectromotive force ^D is added to OA giving the resultant OD, which mustbe also the resultant of the internal ohmic drop OC and the terminal voltageCD. It will be noted that in the closed figure OADCO in Fig. 236, all theelectromotive forces are directed one way around the figure, while the ohmic
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