. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. armature of the machine is exactly reproduced inits field circuit. These reproduced currents are characteristic of alltypes of asynchronous machines, and are called image currents, asthey are actually the reflection from the load currents delivered by thearmature circuit. As the exciter of a machine of this type carries image currentsproportional to the gen
. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. armature of the machine is exactly reproduced inits field circuit. These reproduced currents are characteristic of alltypes of asynchronous machines, and are called image currents, asthey are actually the reflection from the load currents delivered by thearmature circuit. As the exciter of a machine of this type carries image currentsproportional to the generated currents, its size must be proportional tothe capacity of the machine multiplied by the ratio of the excitationand generated frequencies; therefore, in the commercial machines, theexcitation frequency is reduced to the minimum value possible; fromtwo to five cycles per second being suitable for convenient employment. These machines as heretofore constructed are not self-exciting, butas the principle of image current enables the construction of self-exciting alternators, it will be of advantage to have a general under-standing of the separately excited machine under different conditionsof excitation. 1,184 HAWKINS ELECTRICITY. EXCITER Pig. 1446.—Diagram of constant pressure image current alternator connections. The imageor reproduced currents are characteristic of all types of asynchronous machines, and irecalled image currents because they are actually the reflection from the load curreirliverad by the armature circuit. The principle of operation is explained in the aaora<panying text. ALTERNATORS 1,185 When the generated frequency of the machine is equal to the differenceof the excitation and rotation frequencies, the magnetization of themachine is higher under a non-inductive load than under no load. Thisis principally due to the ohmic resistance of the fluid circuit, whichprevents the image current from entirely neutralizing the magneto-motive force of the armatu
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