UK plants are facing volatile energy prices, increased costs, regulatory demands and carbon reduction targets. That's why plant engineers need to focus on optimising energy savings throughout the drive train, says Steve Barker
An area of energy management often neglected is motordriven systems. Yet, these are the largest consumers of electrical energy in the UK, accounting for around 22% of all electricity generated. Further, their energy saving potential has been recognised by government for some time, and hence the increasing regulatory focus on electric motors and driven machines. For example, there are now minimum motor efficiency standards in place.
The fact is that many plants could make significant savings if they considered the full financial implications of running electric motors. For example, a single 75kW motor may cost more than £1m over a typical 20 year lifecycle – making its purchase price just 1% of the cost. So, by reviewing purchasing policy and improving the engineering design of a site, organisations can substantially reduce costs.
For significant savings to be achieved, however, plant engineers would be well-advised to adopt a holistic approach to motor-driven systems and consider the complete drive train. That means starting by auditing everything from the electrical supply right through to the final mechanical output device. What is the form of motor control? Does the system utilise direct on-line, variable speed or soft-start drives? What about the selection of the motors? Are they as efficient as they could be? What is the mechanical configuration? What about the gearbox or coupling arrangement? Are they as efficient as possible?
Lifecycle costs are key
Most systems are purchased for minimum capital cost. Lifecycle costs are often ignored and, even when they aren't, are often incorrectly calculated. It is worth remembering that overall system efficiency – from electrical supply to mechanical output – could be 30% less than calculated. So when designing the system, the driven machine required should first be considered, accounting for the complete profile of its use. The more accurately the system design is defined, the better the system efficiency. Indeed, engineers would be well advised to use simulation techniques to improve predictive calculations and designs.
It is also worth noting that mechanical coupling techniques and gearbox arrangements have a substantial impact on system efficiency. For example, a high-efficiency helical bevel gearbox may be 30% more efficient than a traditional worm box. A robust mechanical requirement ensures that the correct motor can be specified: oversizing should be avoided, as this adversely impacts efficiency. Similarly, the speed and load profile of the motor controls need to be assessed – along with any impact on the main supply.
Then, once all components have been specified, it is crucial that the overall system is not compromised by poor installation practice, incorrect commissioning techniques or lack of appropriate maintenance. The two most common problems in motor-driven systems are incorrect system design, and poor installation and commissioning. That is also why effective asset management programmes are so important. There is a tangible opportunity to achieve significant savings across all motor-driven systems by ensuring that they are managed on a plant-wide basis.
A holistic approach should ensure that inappropriate short-term measures are not required. Remember, when a component fails at an inconvenient time, if a company does not have an effective maintenance strategy, including comprehensive spares, a shortterm – and probably costly – solution will be required.
For higher power ratings or for plant critical applications, users should also consider 'expert systems'. They integrate condition monitoring techniques with control algorithms embedded in an SCADA or process control systems. This provides full integration of condition monitoring and predictive maintenance and can reduce system lifecycle costs by up to 60%.
By implementing a fully integrated, systematic approach to energy management and looking at best practice outlined in the ISO 50001 standard, plant engineers can increase energy savings up to four times. Working with a partner with specific expertise in effective energy management strategies can help.
Steve Barker will be leading discussion of this topic at Answers for Industry (www.siemens.co.uk/afi), a major conference and exhibition hosted by Siemens on 4 and 5 July at Manchester Central Convention Complex.
To book your free place at Answers for Industry on 4th and 5th July at Manchester Central Convention Complex, log on to www.siemens.co.uk/afi
