Small drive offers multipoint positioning

Edited by the Engineeringtalk editorial team Mar 6, 2008

The SJ700 offers multipoint positioning and near servo performance from a standard induction motor.

Silverteam has released 160 to 400kW versions of the Hitachi SJ700 variable speed drive.

The SJ700 features integral easy sequence programmable functionality (EzSQ) as standard.

Its compact size is important for users and systems builders who are seeking to reduce control panel size.

It also incorporates a power switching technology to reduce dVdT, with the IGBT (insulated gate bipolar transistor) stack at the heart of the drive.

High dVdT is associated with motor insulation breakdown, due to the increased terminal voltage of motors when used with AC drives.

"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 offers 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".

An optional feedback card can be used to close the vector loop for 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" Harvey said.

"Its communication with both the external system and the drive's internal circuitry is naturally very fast and very secure".

The large SJ700s are suited to use 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" Harvey said.

The SJ700 also offers benefits for applications where high-performance is not critical.

There are savings because users don't have to buy a separate PLC and receive 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.

Harvey said "We tested all the drives with many different makes of motor".

"Voltage spikes 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 communications options, a 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.