September 2021

36 n INSIGHT September 2021 www.drivesncontrols.com Condition monitoring: a powerful tool for checking drive health F or many years, a common maintenance practice for drives and motors has been“run to failure”. Assets are allowed to continue operating until a breakdown occurs, after which reactive maintenance is performed. The operation in which the asset is being used then has a period of unscheduled downtime while the reactive maintenance is being performed. It then returns to normal operation. However, run-to-failure does not maximise the life of the assets, and the reactive maintenance often requires replacement parts. If suitable spares are not held in stock, an emergency replacement will be needed when a drive or motor fails, leading to additional downtime, especially if there are stock availability or logistics issues. The most common alternative to run-to- failure and reactive maintenance is preventative maintenance, where pre- planned downtime is scheduled in advance and used to perform maintenance activities on assets, with the aim of lengthening the assets’ service lives and preventing breakdowns and unplanned downtime. The major drawback of this approach is the difficulty of setting appropriate maintenance intervals. It is easy to over- maintain a system, leading to excessive expenditure and use of resources. On the other hand, if the scheduled maintenance is not frequent enough, then preventative maintenance becomes similar to a run-to- failure approach, with all of its downsides. Even if the maintenance schedule is appropriate, the stochastic variation in methods and timing of failures may lead to breakdowns and unpredicted downtime, regardless of the preventative maintenance schedule. Much as we may want them to, breakdowns do not follow our schedules! A third approach to maintenance, is predictive maintenance, which aims to limit maintenance interventions – and associated downtime – to times when it’s necessary to prevent an upcoming failure. When implemented correctly, this approach gives the benefits of preventative maintenance – such as minimising unplanned downtime, and maximising the service life of assets – while removing the possibility of over- maintaining, and thus maximising the uptime of the asset. It can be considered as a lean / just-in-time approach to maintenance. Condition monitoring is a key component of predictive maintenance systems. To schedule maintenance interventions when they are needed, it is necessary to monitor an asset’s “health”, in order to predict when a breakdown is likely, and preferably also to receive some indication of how to correct or prevent the issue. This is the “predictive” part of predictive maintenance. Moving parts Predictive maintenance is suitable for any asset that needs to be maintained, so is ideal for drives and motors, and for any machine with moving parts. It involves installing some form of condition monitoring that can give information about the state of the machine. The monitoring system then records the “healthy” state of the asset, when everything is operating as it should. The operating asset is then monitored continuously, comparing its operating parameters with those recorded as the “healthy” state. Any deviation from the “healthy” state – whether abrupt, or gradually over time – indicates the need for a maintenance intervention, which can then be scheduled. On large sites, companies can set up condition monitoring on every piece of equipment and view the health of an entire fleet, but there can also be great benefit from installing condition monitoring on one key asset, upon whose health a process Condition monitoring of motors and drives need not be an expensive way of producing complex data. Rohan Beck, Siemens’product manager for simple motion and drivetrain digitalisation, explains to Drives & Controls that it can offer valuable insights into machine operation at a fraction of what it cost previously. Monitoring the condition of motors and drives can help to maximise their uptime and reduce operating costs