Mechanical and Electrical Engineer Continuing Education Series Electrical Drive and Speed Regulation Systems

Author: Xiao-Zhong Liao
Publisher:
Publish Date: 1998-09-01
Features: Many working machines require electric motors to be able to rotate forward and backward; they must be able to start quickly and brake quickly. For example, the back-and-forth rolling of reversible rolling mills, the hoisting and descending of mine hoists and elevators, and so on. There are two ways to change the rotation direction of DC motors: one is to change the direction of the armature current, and the other is to change the direction of the magnetic flux of the excitation, that is, to change the direction of the excitation current. Since the inductance of the excitation winding is large, the process of reversing the excitation current is much slower than that of reversing the armature current, so for high-speed requirements, frequent forward and reverse reversible systems all adopt this method.