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High-power drives set for Birmingham debut

05 March, 2008

Silverteam is using the Drives & Controls show in April to launch high-power (160–400kW) versions of Hitachi’s SJ700 variable speed drive, following last year’s introduction of smaller versions. The compact drives incorporate a patented power switching technology designed to reduce dV/dT, high values of which are associated with motor insulation breakdown caused by the high terminal voltages of inverter-driven motors.

Hitachi SJ700

"The SJ700 reset the benchmark for small- and medium-sized drives, offering multipoint positioning and near-servo performance from a standard induction motor," says Stuart Harvey of Silverteam, Hitachi’s drives and automation supplier in the UK. "The 160–400kW SJ700 makes similar performance available right through the power range."

The SJ700 is a sensorless vector drive, with 150% torque at zero speed, which includes enhanced autotuning for easy set-ups. An optional feedback card can be used to close the vector loop for even finer control. The drive has on-board PLC functions that are said to avoid the need for external PLCs, even in demanding applications.

Hitachi has designed the SJ700 for a working life of at least ten years. "We tested all the leading drives with many different makes of motor," says Harvey. "Voltage spikes leading to insulation breakdown are always a potential problem, particularly with cable runs over 50m, so we gave the designers the targets of reducing problems to negligible levels and for the drives to be usable with cables over 100m long without line reactors. To achieve this, they could not refine existing techniques, so they had to develop next-generation technologies."

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