Practical electric transmission of power

Contemplate now the complete chain of energy flow from the prime mover, a steam or internal combustion engine, to the point where the mechanical power is finally applied. The transformation at each end must take place with a smooth mutual reaction, based on the second and third principles. This was not properly understood until the 1880�s, so that practical electric transmission of power was delayed until that time. Power that is not delivered to the load is lost as heat in electrical resistance, which is equivalent to mechanical friction. Heat is produced in the generator, transmission lines, and motor, and limits the amount of power that can be handled.
Electrical motors were invented early, in the 1830�s, as soon as the magnetic effects of electrical currents and the magnetic properties of iron became known. The motors of Christic and Pixii are typical of these, which used the repulsion and attraction between electromagnetic poles switched by a commutator. Small motors of this kind are still made for classroom demonstration. Attempts in the 1840�s to make these motors more powerful and larger failed completely, because the magnetic forces do not scale proportionally to distance, and the significance of counter-emf was not known.
The motors of Davenport and of Long in the United States are examples of these unsuccessful attempts to scale up classroom demonstrations to practical size.
More success was encountered in making generators, usually by moving permanent magnets (thereby creating a moving magnetic field) with respect to coils of wire wound around iron cores, to generate alternating currents for supplying arc lights and direct currents for electrolysis tanks (transformer action). These generators all ran quite hot because of their lack of efficiency, but supplied the greater currents required for these applications more cheaply than chemical batteries. This industry evolved into the electrical power industries of later years.
Siemens and Gramme solved the problem of efficiency in the late 1870�s by introducing magnetic circuits that did not change as the armature rotated, so that the electrical reactions were smooth and constant. Siemens� first machine (a generator) of 1866 and Grame dynamo, had smooth armatures with conductors on their surfaces. It was still thought that the conductors actually had to be immersed in the magnetic field to produce forces. Soon it was discovered that if the conductors were put into slots in the armature surface, the same result was obtained. This was far superior mechanically, and also made a smaller air gap possible.
The first long-distance transmission of electrical power took place in 1886 over the 8 km between Kriegstetten and Solothurn in Swizerland. Two Gramme machines in series were used as generators, and two similar machines in series at the other end were used as motors. The line voltage was 2000V, and the wire 6mm in diameter (1/4��). The shaft-to-shaft efficiency was 75%, and the installation remained in service until 1908.
Edison�s famous Z-type dynamos (as direct-current generators are often called) appeared in 1879 to supply his carbon-filament incandescent lamps. These had long fields on the mistaken assumption that this gave a more powerful magnet (like a longer lever), showing how little magnetic circuits were understood at the time. This arrangement allowed a great deal of magnetic leakage between the long arms, and made the flux distribution in the armature nonuniform. Hopkinson, an engineer with Edison�s British company, rationalized the fieldgeometry, making a very good generator of the modern type a few years later. The field was symmetrical with respect to the armature, and short.