Feature Drives & motors


A new approach to energy efficiency


When it comes to energy efficiency, simply specifying an energy efficient motor for the application is not enough – other factors will need to be taken into account. Phil Burge, communication manager at SKF, explains


W


hile replacing or upgrading motors and bearings can make a positive impact on plant efficiency, the market-


ing of some solutions leads engineers to believe that a single solution is the only one that matters. There has, for example, been an extremely successful campaign to promote energy efficient motors; and while these are powerful tools in building efficiency and sustain- ability, some engineers are ignoring what goes on elsewhere and focussing exclusively on the motor. Energy efficient motors should


always be fitted in new builds, but when it comes to system refurbishment or repair it may be that only modest energy savings of just a few per cent can be achieved. One of the reasons for this is that energy wastage may already be greater elsewhere in the system, and changes should have been made here first. In some cases, the introduction of


the new motor has impacted on the efficiency of other system components, with a detrimental effect on energy consumption. Generally speaking, if a motor has been correctly sized and fitted it is likely to be running at around 80 to 85% efficiency, and the gains of switching to a new energy efficient version may be completely counterbal- anced if inefficiencies elsewhere in the system remain unaddressed.


Energy consumption In manufacturing and process equip- ment, motors are rarely used in isola- tion; as a minimum there will also be a gearbox and some form of transmission mechanism involved. These compo- nents will also consume energy, and the specification of all must be considered before any decisions are taken with regard to improving efficiency. In fact, every moving or rotating


component – from the motor to the pump or fan bearings – is, to some degree, relevant to overall energy effi- ciency, and the performance of each


Design Solutions JUNE 2013


component can be calculated and com- bined to produce an overall figure for the system. This is what is sometimes called the ‘holistic’ approach, an all- inclusive evaluation that will repay the extra time and effort involved by open- ing the door to a far more cost-effective system. For example, by simply adjust- ing, rebalancing or realigning drive mechanisms, significant reductions in vibration and heat loss can be achieved, reducing energy consump- tion. This can be extremely beneficial with belt drive transmission mecha- nisms, where energy losses through friction, slippage, noise and heat can potentially be high.


Saving costs


A recent example illustrates how evaluating the system as


In manufacturing and process equipment, motors are rarely used in isolation


a whole helps identify where the greatest inefficiencies are to be found. Triggered by a sharp rise in local energy costs, Indonesian textile plant PT Leuwijaya Utama implemented an urgent cost-saving programme, which involved taking a detailed look at the efficiency of the production system. Investigations showed that 30% of


the factory’s energy consumption was consumed by the twisting machines, which are critical in ensuring fabric quality. So, as well as taking measures to correct electric motor energy losses and optimising


frequency converters for the overall electricity supply, the energy con- sumption of the twisting machinery was examined in closer detail. Inside the Leuwitex twisting


machines, lines of high precision spin- dles are driven by two powerful motors. As these machines operate 24 hours per day, frictional losses (and ultimately energy losses) occur in the rotational motion dependant on the quality of the bearings fitted at the ends of each spindle. With 176 twisting machines incorporating 256 spindles, this clearly presented an opportunity for a major energy saving. By installing SKF E2 deep groove ball bearings, frictional losses were reduced by 30% over a standard SKF bearing and achieved 10% total energy savings. By looking beyond electric motor


efficiency alone, the manufacturer was able to examine and improve the performance of the machinery and of the production system as a whole. Therefore, plant maintenance engi-


neers who have the time, skills or resources to carry out such a holistic evaluation can achieve true machine optimisation. Those operations that do not have the same resources can count on outside specialists, such as those at SKF, to optimise the produc- tion system.


SKF T: 01582 496433 Enter 218 www.skf.com/uk


Drive solution cuts pump maintenance time R


ingsend wastewater treatment works – operated by Celtic Anglian Water (CAW) – uses three 90kW pumps to transfer accumulated water from six storm tanks back to the plant for treatment. The 62,000m3 storage tanks are used during


times of high rainfall to hold the storm flows and act as buffers within the plant. The pumps, however, were prone to ragging caused by debris fouling the pump inlet, so these had to be removed, stripped


down and cleaned, before being re-assembled and lowered back into their housing. The use of an overhead lifting beam, electric hoist and maintenance team meant that the procedure was costly and time-consuming. So, Brendan Riley, CAW’s site maintenance engineer, asked ACS Drives and Control Systems, a member of the ABB Drives Alliance, to provide a solution. ACS installed a trial drive free of charge to prove the effectiveness of the ACQ810 industrial drive from ABB. One


function of this is an anti-ragging technique – when triggered, a cleaning cycle is initiated and operates in a number of user-defined cleaning cycles. The function enables the drive to automatically perform preventive maintenance on the pump. Of further benefit, the cleaning trigger commands are very flexible and adaptable to each process. During the month long trial period, no blockages were experienced and there was no reduction in flow. Following the trial,


a permanent installation was provided for all three pumps, following which CAW have not had to lift the pumps once. ABB


www.abb.co.uk/energy Enter 219 23


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