Drives engineered for energy saving

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Many manufacturers and material processors install variable speed drives simply to allow the machine to have a variable speed. Modern VSDs can also have a variety of industrial sensors incorporated to allow the drive to control the process better, with more control, and save the cost of a PLC or separate controller

By Steve Drumbell

Industrial motors and drives at the heart of a huge range of Australasian businesses represent a major opportunity for energy savings as companies adapt to escalating power prices and the introduction of carbon taxes.

Industrial motor and drive technology has improved greatly in the last 10 years and, with a large effort being spent on make equipment with a greener foot print.

Businesses can save a lot of money by re-assessing how they use energy in the day-to-day running of their business.

Even straight forward initiatives – such as the adoption of variable speed drives (VSDs) instead of fixed speed drives – can generate savings that will more than offset the costs of carbon taxes being imposed in Australia and elsewhere.

VSDs can typically reduce the speed required for particular operations by 20 percent, cutting power bills by more than 30 per cent in some cases and achieving payback in less than a year.

The biggest problem is that the technology is growing so quickly that it can be hard to keep up with all the changes and understand which is the correct option for individual companies.

There are undoubtedly major savings to be made through the use of advanced drives technologies.

In the case of Bonfi glioli, that means advanced and versatile VVVF and vector electronic drives technology, including vector controlled inverters such as the SYN, SLP, ACT, VCB series from the company.

Some of the biggest savings can be made simply by seeing if particular companies have any fans or pumps that are not being controlled by a variable speed drive – typically where the flow of the fan or pump is being controlled by a valve or flow regulator.

Installation of variable speed on these applications can save money and result in a quick payback time because:

  • VSDs are generally around 94-98 percent efficient
  • Current on startup is limited to between 150-200 percent of total motor current (direct online motors can draw between 5-7 times the full motor current on startup)
  • In many pumping applications, it can be very cost-effective to replace the direct online start with a VSD. This can see installation payback in some cases of less the 12 months
  • Where supply authorities penalise companies based upon spikes in demand current, this can be greatly reduced by installing VSDs on motors

Where the use of motors becomes costly is when the motor is started and stopped regularly via a direct online start.

Direct online starting can draw 5-7 times of full load current of the motor out of the supply grid.

This high current inrush fatigues motor windings, generates high heat in the motor and in some cases cause supply grid voltage dips which supply authorities do not appreciate (and may lead to penalties).

VSDs, on the other hand, limit the starting current to between 150-200 percent of full motor current and also smoothly ramp the motor to the required speed.

Advances in drive design and control mean users can generate full motor torque down to virtually zero speed. This will reduce high inrush currents, greatly reduce motor winding fatigue and also allow users to set the correct motor speed for the application.

By putting a VSD onto a common centrifugal pump and reducing the speed by around 20 percent, users can see power savings of about 30-50 percent.

VSDs can also avoid the need for larger size motors. Cost rises may not be highly significant as specifiers go up a size or two to meet their power needs, but this approach will draw excess energy just to keep the heavier rotor turning.

Old practices of running motors direct on-line and using other means to control flow or temperature are still widely used and cost companies a lot of money.

Many manufacturers and material processors install VSDs to simply allow the machine to have a variable speed, but modern VSDs can also have a variety of industrial sensors incorporated to allow the drive to control the process better, with more control, and save the cost of a PLC or separate controller.

Also, many manufacturers and processors think that installing a soft-starter is a better option than a VSD, but in fact the soft-starter will also draw larger currents and may not be able to accelerate the load.

Basic information for a plant efficiency audit includes:

  • What motors you have
  • What kW size
  • The application they are being used for – the resultant effect of the motor being reduced by other means, i.e. pumps flow being reduced by manual flow valves after the motor etc.

Once you have this basic information, you need to look at the applications in which the motor is running at full speed but where the effect of the motor is being limited – as in a control valve limiting water flow, or the motor continually being turned on and off due to it over working the application.

These will be the areas that have the best potential to give the greatest return. If you find you have applications that are being restricted, you are in a very good position to benefit from an external energy audit.

Drive manufacturers are looking at ways to make their VSDs more beneficial to the customer and are starting to design the drives with low-loss drive filters, sleep modes to reduce energy consumption when motors are not running, and load monitoring which will optimize motor current to the application to reduce energy supplied to the motor.

Great benefits are already delivered by technologies such as the Bonfiglioli Vectron Active series, which offers state of the art control of industrial electric motors up to 55kW, complementing EAD equipment in styles and confi gurations up to 800kW.

Generating clean energy – such as sun or wind energy – is expensive and present benefits have been limited.

It may be that simply getting your business run more efficiently will reduce your running costs over the short and long term.

Steve Dumbrell is an application/sales engineer for electronic automation with Bonfiglioli Transmission Australia.

For more information:

Neil Pollington

Tel: 0800 432 777, 021 827 199

Email: [email protected] glioli.com.au

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