VSD cuts saw stoppages

Tata Steel asked ABB authorised value provider, Halcyon Drives, to look at the application and design and install a solution that would solve tripping problems.

Halcyon Drives supplied, installed and commissioned a new ABB 250 kW high efficiency IE2 cast iron, 6-pole motor fitted with an insulated non-drive end bearing. This is controlled by a 200 kW ABB industrial drive, ACS880, housed in an IP54 enclosure.

The VSD is programmed to run at an energy saving speed or full speed, either of which can be selected remotely. When a cut has been completed, the saw motor speed is reduced to 75 percent and initiates a timer. If no further cutting has started for two minutes, the speed is reduced to 50 percent.

The VSD is equipped with a braking system, including a brake chopper and resistors to dissipate heat from the drive while slowing the circular saw. The drive is programmed to monitor overcurrent, with torque monitoring giving a 4-20 mA analogue signal to allow automatic control.

The control system is modified to incorporate this monitoring – although the operator can still control the saw manually, the torque and current monitoring prevent an action that would trip or stall the motor.

An automatic one time overload reset is incorporated into the new drive, to reduce waiting time. Should a trip occur, a second trip within 10 minutes requires an electrician to reset the system.

In the two months since the torque and current protection system was introduced, there have been no reported instances of motor trips. Trials are currently under way to find the optimum traverse speed to optimise the blade life.