Plate Mill Hydraulic Pumps at Xinjiang Bayi Iron & Steel: Drive Plus PMSM Beats Soft Starter

The roll-gap hydraulic system on the plate mill's rolling stand draws oil from a reservoir with four pumps that discharge it as pressurised flow. Each pump was driven by an induction motor started from a Schneider soft starter. Soft starting is a reasonable fit for a pump that only ever needs to run, but it leaves the motor turning at fixed speed, and an induction motor at fixed speed draws its magnetising current whether the mill is rolling or idling between passes.

The retrofit converted three of the four sets — soft starter plus induction motor — to a Yolico YDS8000 series drive with a permanent-magnet synchronous motor. The PMSM's rotor current acts as field excitation, so the power factor can be held close to unity across the load range instead of sagging whenever the pump is not fully loaded, and the drive allows the pump speed to follow demand.

Drive sizing followed the motor's full-load current rather than its power. The synchronous motor is rated 160 kW at 1500 rpm with a full-load current of 271 A, so a 300 A, 160 kW drive was selected. That is the discipline that keeps a PMSM retrofit safe: permanent-magnet motors can draw significant current for the torque they produce and the drive must be able to supply it continuously, not just at the drive's nominal rating.

Commissioning began on the bench rather than on the process. With no load on the shaft the motor parameters were set and the drive run, and only once it behaved correctly was the coupling connected for a loaded test. Because the pump station is part of a rolling line, the changeover was kept to one pump set at a time so the hydraulic system never lost capacity.

The result was measured with an energy meter the customer fitted upstream of the drive. A pump running on the converted set drew 70 A from the supply where the soft-starter cabinet had drawn 86 A, a difference of about 10.5 kW. Running 16 hours a day for 300 days a year, that is roughly 50,400 kWh a year from one pump set. The mill was satisfied enough with the outcome that it plans to convert its remaining asynchronous motors in stages — a population of around 1,000 units, which is where the significance of a 10.5 kW saving per machine becomes clear.