Industrial motors and drives at the heart of a huge range of Australasian metals industry equipment represent a major opportunity for energy savings as companies adapt to escalating power prices and the need for sustainable practices. By Harry Singh, Applications Engineer at Bonfiglioli Transmission Australia.
Businesses can save a lot of money by reassessing how they use energy in the day-to-day running of their business, with ever-larger effort being invested in ensuring that all equipment has a greener footprint. Industrial motor and drives technology has improved greatly in the last decade, so even straightforward initiatives – such as the adoption of variable-speed drives instead of fixed-speed drives – can produce significant energy savings.
Variable-speed drives can typically reduce the speed required for particular operations by 20%, cutting power bills by more than 30% in common instances (such as those following) 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 the most suitable option available for individual companies – especially for firms that haven’t looked at their options for a few years.
Perhaps government has a role here in sponsoring holistic audits of company energy use. These would undoubtedly produce major savings through the use of advanced drives technologies, such as, in the case of Bonfiglioli, advanced energy saving and versatile VVVF and Vector electronic drives technology, including SYN, S2U, Agile, ACT, Active Cube, VCB and ANG series of vector-controlled inverters.
Savings potential
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 drive on these applications has one of the biggest potential to save money and supply a quick payback time by reducing motor speed and thus reducing motor current. This is because:
- Variable speed drives are generally around 94%-98% efficient.
- Current on start-up is limited to between 150%-200% of total motor current. (Direct online motors can draw between five and seven times the full motor current on start-up).
- The advanced static and dynamic energy-saving functions, adaptability and robustness of variable-speed drives reduce the impact on the environment.
- In many pumping applications, it can be highly cost-effective to replace the direct online start with a variable-speed drive. This can in some cases see installation payback of less than 12 months.
- Where supply authorities penalise companies based upon spikes in demand current, this can be greatly reduced by installing variable-speed drives 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 between five and seven times the full load current of the motor out of the supply grid. This high current inrush fatigues motor windings, generates high levels of heat in the motor, and in some cases can cause supply grid voltage dips, which supply authorities do not appreciate (and may lead to penalties).
Variable-speed drives, on the other hand, limit the starting current to between 150% and 200% 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 variable-speed drive onto a common centrifugal pump and reducing the speed by around 20%, users can see power savings of around 30%-50%.
Variable-speed drive can also avoid the need for larger-sized 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.
Outdated practices
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 variable-speed drives to simply allow the machine to have a variable speed, but modern variable-speed drives (such as Active Cube) can also have a variety of industrial sensors incorporated to allow the drive to control the process better, and save the cost of a PLC or separate controller. Outstanding performance in terms of accuracy and response time puts Active Cube in the high-technology end of the Bonfiglioli Vectron drives range.
In addition, many manufacturers and processors think that installing a soft-starter is a better option than a variable-speed drive, but in fact the soft-starter will also draw larger currents and may not be able to accelerate the load. Bonfiglioli was contacted to look at an application that 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 – which subsequently melted the cables.
Bonfiglioli replaced it with a variable-speed drive programmed it for the application. Bonfiglioli could then accelerate the full load carrier smoothly to full speed in five seconds, 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 variable-speed drive.
Audit objectives
Basic information for a plant efficiency audit includes:
- What motors do you have?
- What is their kW size.
- What application are they being used for?
- Is the resultant effect of the motor being reduced by other means? i.e. pumps flow being reduced by manual flow valves after the motor.
Once you have this basic information, Bonfiglioli would look at the applications in which the motor is running at full speed but where the effect of the motor is being limited, such 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 manufacturers are looking at ways to make their variable-speed drives 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. 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 132kW, and the Active Cube series, which has been extended up to 1.2MW.
Generating clean energy – such as sun or wind energy – is expensive and the benefits have at present been limited. It may be that simply getting your business run more efficiently will reduce your running cost over the short and long term.