New benchmark for large drives

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Silverteam will be using the Drives & Controls show to launch the high power versions, 160kW to 400kW, of the Hitachi SJ700 variable speed drive - small and medium sized version having been introduced in 2007.

The SJ700 is a radical development of drives technology, it being the first off-the-shelf unit with integral easy sequence programmable functionality (EzSQ) as standard.

Perhaps the first notable thing about the SJ700 is its compact size, an increasingly important issue as users and systems buiders seek to reduce control panel size. It also incorporates a patented power switching technology to reduce dVdT, with the IGBT (insulated gate bipolar transistor) stack at the heart of the drive. High dVdT is associated to motor insulation breakdown by the increased terminal voltage of motors when used with AC drives.

The smaller drives caused a stir in the market when launched last year, and the new large drives are expected to be even better received.

"Large drives tend to be installed and used for many years so can look very dated by the time they are replaced," explains Stuart Harvey of Silverteam, Hitachi's Drives and Automation Company in the UK. "The SJ700 resets the benchmark for small and medium sized drives, offering multipoint positioning and near servo performance from a standard induction motor. The 160kW-400kW SJ700 makes similar performance available right through the power range.

The SJ700 is a sensorless vector drive, with 150% torque at zero speed and near total immunity to motor constants problems. It sets new levels of responsiveness and accuracy and includes enhanced autotuning for increased ease of set up. An optional feedback card can be used to close the vector loop for even finer control.

"The built-in EzSQ functionality provides a very powerful controller that negates the need for an external unit such as a PLC in even the most demanding of applications," says Harvey. "Its communication with both the external system and the drive's internal circuitry is naturally very fast and very secure. This enhances operational performance all round."

The large SJ700s should set new performance standards in water pumps, fans, hoists, lifts and many other applications. "With lifts, for example, we can offer very smooth floor transitions with adjustable S ramps and brake release confirmation signals, while the superior torque and speed control make it particularly suited in hoist applications like cranes or theatre flying systems."

The SJ700 also offers notable benefits for applications where high performance is not critical. "There are savings because you don't have to buy a separate PLC, panel space savings, installation and commissioning time savings and an increase in reliability."

Hitachi has designed the SJ700 for a working life of at least 10 years. As Harvey puts it: "Every detail has been looked at to design out possible failure modes. The patented switching is just one example of this.

"We tested all the leading drives with many different makes of motor. Voltage spikes leading to insulation breakdown was 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."

Other features of the SJ700 include brake transistors on sizes up to 22kW , integral EMI/RFI filters across the whole range, a full range of comms options, customisable display panel, intelligent energy saving, active frequency matching for restarting and flying load catching, regenerative braking under E-stop conditions and full RoHS compliance.


Silverteam Limited

Tel: +44 (0)1493 669879

Fax: +44 (0)1493 669647

sales@silverteam.co.uk

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