Description

Geared Traction Elevators

Geared traction machines are driven by AC or DC electric motors. As the name implies, the electric motor in this design drives a worm-and-gear-type reduction unit, which turns the hoisting sheave. While the lift rates are slower than in a typical gearless elevator, the gear reduction offers the advantage of requiring a less powerful motor to turn the sheave. These elevators typically operate at speeds from 38 to 152 meters (125-500 ft) per minute and carry loads of up to 13,600 kilograms (30,000 lb). An electrically controlled brake between the motor and the reduction unit stops the elevator, holding the car at the desired floor level.

Contemporary cheaper installations, such as those in residential buildings and low-traffic commercial applications generally used a single or two speed AC hoist machine (abbreviation is AC/(speed number)). The widespread availability of lower-cost solid state AC drives has allowed infinitely variable speed AC motors to be used universally (for ACVV/AC – VVVF), bringing with it the advantages of the older motor-generator based systems, without the penalties in terms of efficiency and complexity. The older MG-based installations are gradually being replaced in older buildings due to their poor energy efficiency.