Curing Overcurrent Trips on a Quarry Wire Saw: Free-Run Stop and Torque Limits

The machine is a wire saw: a 45 kW spindle drives a large disc that pulls a steel wire through the stone, while a small 101-series motor on a travelling carriage keeps the wire in tension through a PID loop. If the wire goes slack the carriage backs off to restore tension. The drive is a YD3045 T4 N rated 96 A, a heavy-duty frame that tolerates 150 % for 60 s and 180 % for 1 s.

The customer reported two different faults. At start, with a 10 Hz command, current could jump to between 90 A and 130 A depending on how the wire lay, and occasionally tripped on OC. In automatic running, at a 35 Hz command with 80–120 A of normal load current, the current would sometimes break away past 140 A and trip instantly.

The fault record made the first problem identifiable. The drive had stored a U2 record at 6.43 Hz output and 156.8 A — a trip during acceleration. The operator mentioned that when it tripped the wire was visibly jerked and the carriage shook. The drive had been set to stop by free-run, so on a trip the output was removed and the disc coasted with the wire under no control at all — in a confined kerf that lets the wire jam. The next start then faced a stalled motor and a locked wire, which is exactly the start-up overcurrent being logged.

The second problem was a tuning and margin question. During automatic running the carriage could retreat faster than the PID intended, spoiling the wire tension, and the drive's torque limit was set at 200 % in all four quadrants, well beyond the 143 % the motor and IGBT combination can actually deliver. Stall prevention during acceleration sat at the default 150 %, letting the drive push 144 A before it would limit frequency.

Three changes fixed both symptoms. The stop mode was changed from free-run to deceleration with a 10 s ramp, so a stop keeps the wire under control. Acceleration stall prevention was lowered from 150 % to 100 %, so frequency stops rising once current reaches the 96 A rating. Torque limits in all four quadrants were brought from 200 % down to 120 %, and the PID proportional gain was reduced so the carriage retreats more gently. Running current settled to 50–80 A and start-up current held under 100 A; two days of cutting confirmed the machine met the customer's expectation with no loss of cutting force.