Historically, AC motors were used for single or double speed elevator machines on the grounds of cost and lower usage applications where car speed and passenger comfort were less of an issue, but for higher speed, larger capacity elevators, the need for infinitely variable speed control over the traction machine becomes an issue. Therefore, DC machines powered by an AC/DC motor generator were the preferred solution. The MG set also typically powered the relay controller of the elevator, which has the added advantage of electrically isolating the elevators from the rest of a building's electrical system, thus eliminating the transient power spikes in the building's electrical supply caused by the motors starting and stopping (causing lighting to dim every time the elevators are used for example), as well as interference to other electrical equipment caused by the arcing of the relay contactors in the control system. COUNT 5
QSN1 Throughout history, what type of engines were used for elevator machines? ANS1 AC motors QSN2 Why were AC motors used? ANS2 cost and lower usage applications where car speed and passenger comfort were less of an issue QSN3 What problem arises for fast and large capacity elevators? ANS3 the need for infinitely variable speed control over the traction machine QSN4 Generally, what powered the relay contoller? ANS4 MG set QSN5 What is a known advantage of the MG set? ANS5 electrically isolating the elevators from the rest of a building's electrical system