Evolution of induction motors-the ever-shrinking motor

The induction motor was invented in the 1880s by Nikola Tesla, and is basically unchanged 100 years later. But there have been tremendous changes. One of the most notable is the change in physical size. Progress in induction motors, spurred by keen competition, has been notable. One indication of this progress is the change in specific weight (pounds of material per motor horsepower) and specific purchase price (dollars per horsepower). Better operating characteristics, greater reliability and versatility, and longer life have been the result of steady progress in the motor industry. Some of the long-term trends have resulted from changes in: construction-open to more protected enclosures; bearings-sleeve bearings to antifriction bearings; stator windings-form coils to random windings and served wire to enameled wire; rotor windings-fabricated copper to cast aluminum and development of double cage rotor slot designs; starting methods-reduced voltage to full voltage starting. Standardization has played a large role in motor progress