With their ability to vary the speed of a driven motor to match the demands of a process, variable-speed drives are well known for their role in saving energy. They can also play a key role in maintaining productivity, achieving quality targets and assuring safety.

Yet, none of these abilities matter if the drive is not working because it has suffered some failure. 

Although drives are very reliable, one of the major reasons for failure is poor or even non-existent maintenance. It is estimated that 80% of drive failures occur due to a poor maintenance regime.

Whole life approach

Yet, good maintenance is not the whole story. To really understand how to get the most out of drives, we need to understand the whole life cycle of a drive.

Drives go through four phases in their lives – Active, Classic, Limited and Obsolete. The Active phase is the sales and manufacturing phase, following which the product moves into the Classic phase. Complete life cycle support is guaranteed throughout these two phases. 

In the Limited phase, product support is ramped down, ending in the Obsolete phase where product support is no longer available (retrofits or replacements are offered at this stage).

So we need to get a full picture of what might happen to the drive in the future and what to do about it. What life cycle phase is it in? What of its history in service? Has it been maintained properly in the past? Is the application critical to production or safety?

This is the aim of a life cycle assessment or LCA. Its first task is a site survey of the installed drives, where the life cycle status of the drives is assessed, their condition is evaluated and installation procedure checked. The final stage is a comprehensive inventory and life cycle report, including recommendations. 

One of the main benefits of a life cycle audit is that it provides knowledge of the drives’ condition, helping maintenance planning and costing. It also helps prolong the life of the drives, avoid premature failure and helps life cycle planning and budgeting.

Putting plans in place

Essentially, the proposed life cycle management plan implements recommendations from the life cycle assessment, developing preventative maintenance schedules for each individual drive and implementing appropriate retrofits/replacements as appropriate 

Another aspect that is identified is how critical each drive is to the operation of the process. 

Three levels of criticality are defined, according to various criteria which are recorded during the lifecycle audit. 

These are:

•  Business Impact (financial, environmental, safety)

•  Drive stress

•  Known maintenance history

•  Operating conditions which may increase risk of failure (ambient temp, exposure to corrosive gases or conductive material, moisture, dust)

A Criticality matrix is then produced allowing maintenance decisions to be made according to which drives are the most critical to the operation of the plant

Assessing drives in this detail allows a maintenance plan to be formed for each area of the plant that uses drives. This programme will recommend replacement, upgrade or refurbishment, a major preventive maintenance action or a basic preventive maintenance action. This plan ensures the right resources and investments can be provided at the right time. 

The main benefit of life cycle management is that it enhances the condition and reliability of drives and extends their operating life by using the correct resources and parts.

Taking a whole life approach to drive servicing and replacement is the only sure way to get cost-effective, extended use from these valuable plant assets and in turn ensure that quality, safety, compliance, production time and revenue is maximised.