On this day in 1892 Nikola Tesla was granted the patent for SYSTEM OF ELECTRICAL TRANSMISSION OF POWER. U.S. Patent No. 487,796.
This invention is an improvement in systems of electrical distribution of power wherein are employed motors having two or more independent energizing circuits, through which are passed alternating currents differing in phase that are produced by a magneto electric machine having independent induced circuits, or that are obtained from any other suitable source or by any other suitable means. In illustration of the various conditions which is regarded as most important to an attainment of the best results from the use of motors of this character, generally forms of generator have been used in which the relations of the induced or current-generating coils and field-magnets were such that but two impulses or current are produced in each coil by a single revolution of the armature or field cores. The rate, therefore, at which the different phases or impulses of current in the line-circuits succeeded one another was so little greater than that at which the armature of the generator revolved that without special provision the generator required to be run at very high speed to obtain the best results. It is well known that the most efficient results are secured in the operation of such motors when they are run at high speeds; but as the practicable rate of speed is much limited by mechanical conditions, particularly in the case of large generators, which would be required when a number of motors are run from a single source, Tesla sought to produce a greater number of current impulses by a slow or slower speed than that at which the ordinary bipolar machines may be economically operated. Therefore the system has adapted to this system any of the various types of multipolar alternating-current machines which yield a considerable number of current reversals or impulses for each revolution of the armature by observing the main condition essential to the operation of my system that the phases of the currents in the independent induced circuits of the generator should not coincide, but exhibit a sufficient difference in phase to produce the desired results. This may be accomplished this in a variety of ways, which, however, vary only in detail, since they are based upon the same underlying principle.
Another feature of this invention is in the plan which was devised for utilizing generators and motors of this type, whereby a single generator may be caused to run a number of motors either at the same speed as its own or all at different speeds. This is accomplished by constructing the motors with fewer poles than the generator, in which case their speed will be greater than that of the generator, the rate of speed being higher as the number of their poles is relatively less. This will be understood from an example. Suppose the generator has two independent generating-coils which revolve between two pole pieces oppositely magnetized and that the motor has energizing-coils that produce at any given time two magnetic poles in one element that tend to set up a rotation of the motor. A generator thus constructed yields four impulses or reversals of current by each revolution, two in each of its independent circuits, and I have demonstrated that the effect upon a motor such as that mentioned is to shift the magnetic poles through three hundred and sixty degrees. It is obvious that if the four reversals in the same order could be produced by each half-revolution of the generator the motor would make two revolutions to the generator’s one. This would be readily accomplished by adding two intermediate poles to the generator or altering it in any of the other equivalent ways above indicated. The same rule applies to generators and motors with multiple poles.
