Changing market for DC drives: DC drives are increasingly being used in retrofits, as an example at a steel mill shows

In recent years, the DC drive market has changed and retrofits have become an important market for DC drive manufacturers. An example for DC drives increasingly being used in retrofits is a solution provided recently by Sprint Electric.

The manufacturer of DC drives from Arundel, England, supplied DC drives for a cold rolling steel mill at Graham Perry Steels in Wolverhampton near Birmingham, England. The rolling mill at the site reduces high carbon steel to strips that are used for applications in a wide range of industries. The original drive system of the mill was based on two resistor-based DC drives. The drives were functioning, but obsolete, and were becoming time consuming and expensive to maintain. One drive controlled a 110 kW motor powering the main rolling mill through a right angel reducer gearbox and a two-way splitter box. The other drive controlled a 80 kW motor used for the winding-on assembly that recoils the rolled steel coming out of the mill. This second motor was failing and needed to be replaced along with the drives.

Initial analysis had shown the control system as a whole was operating at less than 50 percent capacity, making complete replacement the optimum solution when maintenance time and projected increases in output were considered. A completely new control system was designed by industrial products and services supplier Wyko. The drives and motor specialists chose DC drives from Sprint Electric to replace the old DC drives. Two 185 kW regenerative, digital PLX DC drives were fitted into two new control panels, in addition to a new DC motor.

The upgrade of the drive system resulted in a five-fold increase in production. The control and power upgrade has increased the steel throughput from 80 ft per minute to a rate of 300 ft per minute, and will run up to 1,000 ft per minute after additional scheduled service work has been completed on the main splitter gearbox. This is an impressive increase considering that the rolling mill can exert a million tonnes of pressure to reduce the 8 mm thick carbon steel to 2 mm thick strip.

Increase in productivity and lower energy consumption make DC drives ideal for retrofits when a more cost effective, modern drive system is required. “Retrofits have become an important market for DC drive manufacturers”, says Gary Keen, export sales manager with Sprint Electric. “The large traditional OEM customer basis is moving overseas, as is a lot of the DC market place. In this changing industrial climate, manufacturers that stay in the market find growing opportunities in retrofits.”

Besides the metal processing industry, other applications that can equally benefit from retrofits include the pulp and paper industry, rubber and plastic processing, lifting equipment, food processing, pharmaceutical and chemical manufacturing. DC drives from Sprint Electric being used in retrofits cover a power range from 0.37kW to 265kW. Over fifty models are available, analog or fully digital, covering both single phase and three phase, regenerative and non-regenerative applications, from low voltage servo performance controllers to highly sophisticated fully digital three phase DC variable speed drives of many hundreds of amps.