Traction elevators are the most common type of elevators. Elevator cars are pulled up by means of rolling steel ropes over a deeply grooved pulley,commonly called a sheave in the industry. The weight of the car is balanced by a counterweight. Geared traction machines are driven by AC or DC electric motors.
Such elevators are used where cost of installation needs to be cheaper, such as those in residential buildings and low-traffic commercial applications. In such applications, a single or two speed AC hoist machine is generally used. The widespread availability of solid state AC drives has allowed infinitely variable speed AC motors to be used universally, bringing with it the advantages of the older motor-generator based systems. The VVVF drives (V3F) is responsible for the smooth operation of the elevators.