Rolling Mills, Supply and Control

Originally, motive power was essentially steam-powered. The first "modern" solution dates back to 1891, and was developed by an American engineer, Harry Ward Leonard (1861-1915), known as the Ward Leonard Group (WL).

As early as the 1930s, there were numerous patents for static conversion systems based on mercury vapor rectifiers, not only for rolling mills but for many other applications as well (such as rail traction), and these remained in use until the late 1950s. The advent of the -thyristor definitively condemned these solutions, which were difficult to use and maintain.

It was around 1965 that the era of the thyristor, for reduced power ratings (~ 100 kW), began. The idea of the thyristor was proposed by William Schockley in 1950 and industrialized by General Electric in 1956. With the thyristor, the so-called Graetz bridge topology, named after the German academic Leo Graetz (1856-1941), became widespread... All variable-speed drives used in steel mills now combine Graetz thyristor bridges and direct-current machines. From a rolling point of view, these solutions gave complete satisfaction, increasing -production volumes while respecting the growing quality of products.

By the end of the 1970s, the first controllable power components - bipolar transistors, GTOs and even IGBTs - had appeared, making it possible to supply loads with cosine phi behind, such as asynchronous machines. At the same time, research by both industry and universities has led to very good dynamic performance of AC machines. These machines, once their performance was compatible with processes, replaced DC machines, which were difficult and costly to maintain due to wear on commutators and brushes. In the 1980s, all motorization switched from DC machines to variable-frequency AC machines.

This article is intended for electricians whose job it is to select and specify machines. It also discusses the main algorithms encountered in rolling mills, in particular the various speed controls that take into account the elasticity of rolled products and the torsion of drive shafts. The simulations described are numerical examples related to industrial applications. In order to be accessible to the widest possible audience, this article uses simple, conventional analysis methods.