The project, carried out by by Hidroin_eniring d.o.o. of Ljubljana, was to improve the reliability of the massive fan supplying hot air from the output of the cement oven. One critical feature of the control is to avoid the huge, four-metre fan running at its resonant frequency, causing a build-up of vibrations, oscillation ａnd damage to the fan.

Everything about this installation is massive. The fan motor alone weighs more than six tonnes, the main shaft diameter is 140-mm, each of the four cables to the motor comprises three 240-mm diameter wires ａnd the current on the 690 volt system exceeds 1,000 amps! Not surprisingly, the drive chosen for the task is equally substantial – a Unidrive SP modular drive with one ｍaster unit ａnd eight slave modules that, together, make up the required total of 1 MW. The ｍaster unit is additionally fitted with an SM Profibus DP module to give direct communications to the SCADA control system ａnd an SM Ethernet module for remote monitoring ａnd access.

The motor selected for this onerous duty is a 690V LEROY-SOMER FSA 3-phase asynchronous fan motor, designed for a long service life in extreme operating conditions such as being adjacent to this cement oven.

The drive panel built ａnd installed by PS Logatec, is located in an air-conditioned plant room at the cement works.

Sensors on the fan detect the build-up of vibrations ａnd feed back to the SCADA system. During operation, the system ensures that the fan motor accelerates or decelerates rapidly through the critical frequencies. An additional small motor, separated from the main motor by an electrically operated coupling, is also fitted to the motor shaft to turn the fan slowly when it is not in use to prevent heat damage from the furnace.

Because the Unidrive SP is modular, the customer has complete security of operation, since, even if one module does fail, the drive is capable of running at reduced power.