On this day in 1886 Nikola Tesla was granted the patent for COMMUTATOR FOR DYNAMO ELECTRIC MACHINES. U.S. Patent No. 334,823.
This invention relates to the commutators on dynamo – electric machines, especially in machines of great electromotive force, adapted to are lights; and it consists in a device by means of which the sparking on the commutator is prevented.
It is known that in machines of great electromotive force-such, for instance, as those used for are lights—whenever one commutator bar or plate comes out of contact with the collecting brush a spark appears on the commutator. This spark may be due to the break of the complete circuit, or of a shunt of low resistance formed by the brush between two or more commutator-bars. In the first case the spark is more apparent, as there is at the moment when the circuit is broken a discharge of the magnets through the field-helices, producing a great spark or flash which causes an unsteady current, rapid wear of the commutator bars and brushes, and waste of power. The sparking may be reduced by various devices, such as providing a path for the current at the moment when the commutator segment or bar leaves the brush, by short-circuiting the field-helices, by increasing the number of the commutator-bars, or by other similar means; but all these devices are expensive or not fully available, and seldom attain the object desired.
This invention enabled to prevent the sparking in a simple manner. For this purpose it is employed with the commutator – bars and intervening insulating material mica, asbestus paper or other insulating and preferably incombustible material, which the user arranges to bear on the surface of the commutator, near to and behind the brush.
