Cableform of the USA has patented new digital DC controls which, it claims, for the first time brings Isolated Gate Bipolar Transistor (IGBT) power technology to steel mills and industries using large DC hoists and cranes.
An IGBT is a large power semiconductor. Cableform’s marketing and sales director, Richard Shannon, explained: “The importance of the IGBT in DC electrical use is that to fire it you send a low voltage signal to the gate. To turn it off you simply remove that signal.” He added: “IGBTs have been used in AC electrical applications for many years – in AC variable frequency drives for AC motors, for example. They were not available for use in DC applications until the early 1990s when the first IGBTs became available that were just big enough to handle the heavy current (amps) required in small DC electrical applications. We now use IGBTs that are 2000V/2000A devices to drive large DC motors.” Cableform claims that its LMC Hoist Controls improve performance and reliability, reduce power requirements and eliminate contactor/resistor panels and thyristor controls. They can be fitted to old or new hoists and cranes and are available for DC motors running on power supplies from 200V DC to 750V DC.
“We developed the LMC Hoist Control for DC cranes with the assistance of Bethlehem Steel,” said Shannon. “The first hoist control was installed in February 1999, and has now run without a failure, nor a repair, for almost a year. It’s on a loading dock crane and there is a counter on the hoist that increments with each lift so that we know the exact activity. The unit runs 24 hours a day, 7 days a week and makes on average 8,200 lifts every month.” Cableform began developing LMC-IGBT controls in 1992 for the underground mining industry to drive large DC traction motors from DC overhead supplies. Since that time they have almost become the standard for use in many countries around the world, Shannon said. Before LMC controls, DC traction motors in mines used the same contactor/resistor controls that are used on most DC cranes and hoists today.
In 1997 Cableform developed the first LMC controls for DC bridge and trolley motions, and then set about developing the hoist control which was first installed for Bethlehem Steel, Burns Harbor Division. A patent for the LMC Hoist Control was applied for, and received, based on the electronic control of the hoist motor with microprocessor logic and IGBTs to drive the load.
The company began marketing to the DC hoist and crane industry in September 1999.
“It is quite new to the industry but it has been proven to work,” claimed Shannon.
“The greatly improved reliability and performance are extremely important because, for the first time, it allows DC crane users to reduce maintenance costs, and improve operations, plus have an inexpensive platform for all levels of automation. LMC Controls provide all the functions to DC motors that AC variable frequency drives provide to AC motors.”
