What is Electric Motor ?

press.[18] Due to the high cost of primary battery power, the motors were commercially unsuccessful and bankrupted

The currents are seen to be approximately sinusoidally distributed around the rotor periphery and to be located so as to produce a counterclockwise torque on the rotor

Davenport. Several inventors followed Sturgeon in the development of DC motors, but all encountered the same battery cost

This torque acts to accelerate the rotor and to rotate the mechanical load

issues. No electricity distribution system was available at the time. No practical commercial market emerged for these

As the rotational speed of the rotor increases, its speed relative to that of the rotating field decreases.

motors.[19]

In 1855, Jedlik built a device using similar principles to those used in his electromagnetic self-rotors that was capable of useful

work.[9][15] He built a model electric vehicle that same year.[20]

A major turning point came in 1864, when Antonio Pacinotti first described the ring armature. This featured symmetrically-

grouped coils closed upon themselves and connected to the bars of a commutator, the brushes of which delivered practically

non-fluctuating current.[21][22] The first commercially successful DC motors followed the invention by Zénobe Gramme who, in

1871, reinvented Pacinotti's design.

A benefit to dc machines came from the discovery of the reversibility of the electric machine, which was announced by Werner Siemens in 1867 and observed by

Pacinotti in 1869.[6] Gramme accidentally experimented it on the occasion of the 1873 Vienna World’s Fair, where he showed that his dynamo could be used as a

motor, which he demonstrated to great effect at exhibitions in Vienna and Philadelphia by connecting two such DC motors up to 2 km from each other, using one as a

generator.[23]

The drum rotor was introduced by Friedrich von Hefner-Alteneck of Siemens & Halske to replace Pacinotti’s ring armature in 1872, thus improving the machine

efficiency.[6] The laminated rotor was introduced by Siemens & Halske the following year, achieving reduced iron losses and increased induced voltages. In 1880,

Jonas Wenström provided the rotor with slots for housing the winding, further increasing the efficiency.

In 1886, Frank Julian Sprague invented the first practical DC motor, a non-sparking device that maintained relatively constant speed under variable loads. Other

Sprague electric inventions about this time greatly improved grid electric distribution (prior work done while employed by Thomas Edison), allowed power from electric

motors to be returned to the electric grid, provided for electric distribution to trolleys via overhead wires and the trolley pole, and provided control systems for electric

operations. This allowed Sprague to use electric motors to invent the first electric trolley system in 1887–88 in Richmond, Virginia, the electric elevator and control

system in 1892, and the electric subway with independently-powered centrally-controlled cars. The latter were first installed in 1892 in Chicago by the South Side