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Next-generation drives ‘deliver 12% extra energy savings’

23 September, 2015

Mitsubishi Electric has announced a new generation of variable-speed drives which, it claims, can deliver an extra 12% of energy savings over standard variable torque curve operation. The FR-F800 drives are also said to offer other benefits including optimised speed control, simple start-ups, auto-detection of faults, enhanced communications, high reliability, and auto-tuning of induction or permanent magnet motors.

The F800 is designed primarily to control fan and pump motors, but can also be used for compressors and other applications. Initially there are six models, three in ratings from 0.75–110kW for 200–240V operation , and three in ratings from 0.75–630kW, for 380–500V supplies. They are said to be 98% efficient.

The inverters incorporate a “unique” function, called Advanced Optimum Excitation Control (AOEC), that adjusts the motor current constantly to achieve high torque levels at the same time as high efficiency. According to Matt Handley, Mitsubishi’s product manager for drives in the UK, previous systems have required a compromise by optimising either for performance or efficiency.

Another unusual aspect of the VSD is that it can auto-detect pump operating curves using a series of speed and torque points, unlike other systems that rely on a single point to activate trips. The drive can detect the torque curve of an attached pump or fan and react appropriately, eliminating nuisance trips caused by unusual, but not critical, load variations. It can sense both pump overloads (caused by blockages, for example) and under-loads (caused by broken belts or impellers).

The drive has an on-board PLC and two PID (proportional integral derivative) loops. The 6,000-step PLC (based on Mitsubishi’s L series) supports IEC 61131 programming and expandable I/O (via three option slots).

The dual PID capability allows the inverter to control a motor and other external equipment at the same time, avoiding the need for an external controller. The PID functions include a pump-priming function, upper and lower limit pre-warnings, and protection against burst pipe bursts, dry running and water hammer.

The drive can control several pumps, allowing variable-speed control to be applied to some of them, while the others are running effectively direct on-line (DOL). It can run pump-cleaning cycles automatically, to a schedule, or on demand.

When controlling fans, the drive can detect broken belts and the built-up of material on their blades. It can ensure a smooth restart after a power failure by auto-detecting the fan speed and “catching” it automatically.

To minimise energy consumption, all unnecessary circuits are shut down during standby. The drive’s “intelligent” cooling fans activate only when a set-point temperature has been reached.

In the event of an emergency, a fire override mode will keep extraction fans and water pumps running – even to the point of the F800’s total destruction.

Mitsubishi's new-generation variable-speed drives initially span ratings from 0.75–630kW

A motor preheat function helps to achieve smooth start-ups, to overcome condensation, and to prevent damage caused by freezing outdoor conditions. Vibration caused by mechanical resonances can be detected and reduced, protecting equipment from excessive wear, mechanical damage and premature failure.

The drives offer plug-and-play auto-tuning for high-efficiency permanent magnet motors as well as for induction motors. For ease of set-up, a one-touch “digital dial” allows direct access to all of the important parameters.

An optional, removable six-line LCD panel includes an easy start-up wizard function. The display can also show customised text messages. 

The drive can be used to control external cooling fans in control panels, based on the control panel temperature, thus avoiding the need for a thermometer in the panel.

Critical internal components such as power capacitors and cooling fans are monitored to allow predictive maintenance. To enhance the reliability of the F800 – which comes with a three-year warranty – fault-finding is aided by built-in data-logging and tracing functions. As well as long-term data-logging, the VSD saves status information from before and after an alarm, and can store it, ready for subsequent analysis. This data can be exported using a USB memory stick, which can also be used to store and transfer parameters and PLC code.

A two-channel STO emergency stop provides a safe shutdown to avoid possible damage to the drive.

The drive supports RS-485, Modbus and BacNet as standard, with support for other protocols – including CC-Link, Profibus, Ethernet, EtherCat, SSCNET III, DeviceNet and Lonworks – available as options. Measured energy savings can be displayed via a network.

The F800 inverters are similar in price and size to the previous F700 generation. Existing installations can be upgraded in a simple unplug and swap-out process. The drives are designed to operate for at least ten years.

As well as the general-purpose FR800 drives, Mitsubishi will be offering an application-specific models, known as 800+, for applications such as reel-to-reel winding systems, tunnels and HVAC systems.

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