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Boosting productivity with the help of variable speed drives

Boosting productivity in a process means different things to different people within manufacturing plants.

It could mean enhancing the quality of the end-product or increasing the throughput of production. Alternatively it may be a need to reduce the electricity consumed by the process while at the same time meeting carbon dioxide emis sion limits that may have been imposed.

Yet another aim may be to maximise the process up-time while at the same time minimising the costs associated with maintenance.

And while achieving all these things, the end user can ill afford to take their eye of the current legislation, regulations and directives.

The one simple product that can have an impact on all these productivity goals is the variable speed drive (VSD).

Throughout the food and beverage sector some 65 per cent of all electricity consumed is by electric motors.

Motors are everywhere: in fans, pumps, conveyors, mixers, centrifuges – the list goes one. For example, the high electrical costs of operating cold storages can be reduced by varying the motor’s speed.

And yet only about five per cent of motor-driven applications use a variable speed drive to regulate and control the speed and torque.

The rest use fixed speed motors. Traditionally, applying a VSD to these applications is a good way to save energy. But there are many other, just as compelling arguments, as to why a VSD should be used to enhance the produc tivity goals described above.

A VSD enables a process to achieve fast and accurate speed and torque control while maintaining the repeata bility demanded by the production line.

Enhancing quality

This optimal process control leads to a more consistent quality end-product, which means the best profit for the customer.

For example, some VSDs feature application macros, which are routines dedicated to say, pumps, conveyors or other uses.

A pump macro can maintain product consistency by commanding the drive to start additional pumps in response to a pressure drop, should there be a surge in demand.

As well as dedicated pump control, the VSD provides a pre-pressurisation for process start-ups.

Increasing throughput

Process equipment is usually designed to cater for future productivity increases. Changing constant-speed equipment to provide higher production volumes requires money and time.

With the VSD, speed increases of 5 to 20 per cent are not a problem, and the production increase often can be achieved without any extra investment.

Energy saving

Given that power consumption savings of 50 per cent can be made by reducing the motor speed by just 20 per cent.

And with payback times being as short as six months, VSDs are arguably the one product that can have the maximum impact of a company’s energy and carbon reduction policy.

Maximising uptime

Variable speed drives have many internal functions which can provide better process control.

With inputs and outputs (I/Os), for example, different kinds of process information can be fed to the drive and it will control the motor accordingly. Alternatively, the load can be limited to prevent nuisance faults and to protect the working machine and the whole drive system.

Furthermore, VSDs provide fieldbus technology that enables process equipment to integrate with plant control systems.

This improves the process control as well as the knowledge and information that can be collected from the process.

Minimising maintenance

Being able to vary the speed and torque of an electric motor means there is less wear and tear on the motor and the driven machine.

For example, the ability to bring a process up to speed slowly prevents the sudden shock loading that can damage a motor and the driven machine over time. To ensure the uptime of a VSD, many are equipped with temperature, load, under/ overvoltage protection and warning features.

The real-time clock allows timed tracing of faults so users know what happened and when.

To help avoid any issues with VSDs, adopting a preventive maintenance program helps reduces the risk of failure and increases the lifetime of the VSD, thus lowering the overall operational costs.

Preventive maintenance consists of annual inspections and component replacements according to the VSD specific maintenance schedules.

Regulations and directives

The food and beverage sector is subjected to much legislation. With combustible dust found in flour and grain handling industries, the risk of ignition is high.

Special requirements are set for machine surface temperatures, bearings and critical components.

[Rajesh Maker is Product Manager, Discrete Automation and Motion, ABB Australia.]

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