Geared to save energy

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 carbon taxes.

Industrial motor and drives technology has improved greatly in the last 10 years and, with a large effort being spent on make equipment have 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 straightforward initiatives – such as the adoption of variable speed drives instead of fixed speed drives – can produce savings that will more than offset the costs of carbon taxes being imposed in Australia and elsewhere. 

Variable speed drives can typically reduce the speed required for particular operations by 20 per cent, cutting power bills by more than 30 per cent in common instances 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. This is especially true if companies haven't looked at their options for a few years.

Perhaps the government has a role here in sponsoring holistic audits of company energy use which would undoubtedly produce major savings through the use of advanced drives technologies.

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 a variable speed on these applications has, possibly, the biggest potential to save money and enable a quick payback time by reducing motor speed and thus reducing motor current.

This is because:

  • Variable speed drives are generally around 94 to 98 percent efficient. 
  • Current on startup is limited to between 150 to 200 percent of total motor current. On the other hand, direct online motors can draw between five to seven 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 variable speed drive (VSD). In some cases, this can see installation payback in less the 12 months.
  • Where supply authorities penalise companies based upon spikes in demand current, this can be greatly reduced by installing VSD on motors.

Stop-start operation

Motors generally are reasonably efficient when running continuously and, with the MEPS standard for motor efficiencies, this has been improved in recent years.

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 five to seven times 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 percent and 200 percent of full motor current and also smoothly ramp the motor to require 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 around 30 to 50 percent.

VSD 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 draws excess energy just to keep the heavier rotor turning. 

Outmoded practices

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

Advances in drive design and control mean users can generate full motor torque down to virtually zero speed.Many manufacturers and material processors install VSDs Drives 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.

They also save on 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. 

I was called into look at an application which already had a soft-starter installed but could not drive the full load up a steep incline if it was stopped on the incline.

The full load motor current was 25.4 amps but the soft-starter was allowing the motor to draw 120 amps. This subsequently melted the cables. 

We replaced it with a VSD and programmed it for the application. We could then accelerate the full load carrier to full speed in five seconds, smoothly and the motor was only drawing a maximum of 39 amps.

This was a great application to show the improved performance that can be achieved by using a VSD.

The basic information for a plant efficiency audit includes:

  • What motors you have?
  • What kW size?
  • For what application are they being used?
  • Is the resultant effect of the motor being reduced by other means; for example, pump flow being reduced by manual flow valves after the motor?

Once you have this basic information, I would 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 overworking the application.

These will be the areas that have the largest 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 design

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 optimise motor current to application to reduce energy supplied to the motor.

Vectron Active frequency  converters offer advanced control of electric motors up to 55 kW.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 55 kW, complementing EAD equipment in styles and configurations up to 800 kW.

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 to run more efficiently will reduce your running cost over the short and long term.

[Steve Dumbrell is Automation Applications Engineer, Bonfiglioli.]

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