What is Electric Motor ?

DC motors

This figure shows the effect of these currents in producing a magnetic field across the air gap of the machine for six instants in a cycle. For simplicity,

only the central conductor loop for each phase winding is shown.

At the instant t1 in the figure, the current in phase a is maximum positive, while that in phases b and c is half that value negative.

After many other more or less successful attempts with relatively weak rotating and reciprocating apparatus Prussian Moritz von

Jacobi created the first real rotating electric motor in May 1834. It developed remarkable mechanical output power. His motor set a

The result is a magnetic field with an approximately sinusoidal distribution around the air gap with a maximum outward value at the top and a maximum inward value at the bottom.

At time t2 in the figure (i.e., one-sixth of a cycle later), the current in phase c

world record, which Jacobi improved four years later in September 1838.[16] His second motor was powerful enough to drive a

is maximum negative, while that in both phase b and phase a is half value positive

boat with 14 people across a wide river. It was also in 1839/40 that other developers managed to build motors with similar and

The result, as shown for t2 in the figure, is again a sinusoidally distributed magnetic field but rotated 60° counterclockwise.

then higher performance.

Examination of the current distribution for t3, t4, t5, and t6 shows that the magnetic field continues to rotate as time progresses.

The field completes one revolution in one cycle of the stator currents.

Thus, the combined effect of three equal sinusoidal currents, uniformly displaced in time and flowing in three stator windings uniformly displaced in angular position

The first commutator DC electric motor capable of turning machinery was invented by British scientist William Sturgeon in 1832

is to produce a rotating magnetic field with a constant magnitude and a mechanical angular velocity that depends on the frequency of the electric supply.

The rotational motion of the magnetic field with respect to the rotor conductors causes a voltage to be induced in each,

proportional to the magnitude and the velocity of the field relative to the conductors. Since the rotor conductors are short-circuited together at each end, the effect will be to

Following Sturgeon's work, a commutator-type direct-current electric motor was built by American inventor Thomas Davenport,

cause currents to flow in these conductors

which he patented in 1837. The motors ran at up to 600 revolutions per minute, and powered machine tools and a printing

In the simplest mode of operation, these currents will be about equal to the induced voltage divided by the conductor resistance.

The pattern of rotor currents for the instant t1 of the figure is shown in this figure.