Plant & Works Engineering
How a whole life approach boosts production reliability
Published:  06 September, 2021

A whole life cycle approach can help reduce the risk of sudden failures and provides a smooth pathway for managing replacements and upgrades. PWE reports.

Variable speed drives (VSDs) are extremely reliable and can provide many years of incident-free operation, and a lifespan of several decades.

However, their high reliability can sometimes create a false sense of security. If a VSD is operating in good conditions - away from dusty environments, extreme temperatures and hazardous areas – then it can have a mean time between failure (MTBF) of over half a million hours or the equivalent to 62 years.

However, VSDs are not indestructible, and every unit, if left without maintenance, will eventually fail. If the VSD or its components are obsolete it may be very difficult to repair quickly, potentially leading to costly downtime. Having to replace an obsolete drive at short  notice is also a headache that operators can do without, particularly if production backlogs are mounting up.

While VSDs may not be the most expensive capital equipment in a facility, they have a high in-service value, and the cost of a device failure can be great in terms of lost production. Even so, it is estimated that up to 80 percent of VSDs in the UK are operated without any kind of systematic maintenance program in place. This makes it more likely that, when failures occur, they will occur unexpectedly.

There are three main reasons why a VSD can typically fail:

Using the wrong drive – The VSD may have been chosen to incorrect specifications, or maybe wrongly sized and are therefore having to work too hard for the given application, leading to premature wear. This can also be caused by running a drive over capacity.

Incorrect installation – Poorly dimensioned cabinets can create airflow issues, while excessively high or low ambient temperatures can affect operation if not mitigated. Loose connections can also be a potential culprit in drive failures, while areas with high levels of moisture can lead to corrosion of circuit boards over time.

Poor maintenance – The risk of VSD failure is increased if basic maintenance duties are not carried out, for instance replacing fans per manufacturer’s recommendation, checking connections, annual inspections and cleaning. Fans may become worn or blocked leading to overheating and failure of capacitors. For every 10 degrees rise in operating temperature, capacitor life is halved, and conversely, every 10 degrees reduction will double its lifespan.

The first two causes can be largely remedied by using a trusted, approved partner to supply and install the VSD. However, providing regular maintenance is an ongoing challenge and not a one-off fix. This can make it hard to implement effectively, particularly if local maintenance resources are stretched.

Basic maintenance tips

Whilst VSDs are often employed to carry out a simple job (such as speed controlling a motor), they are highly complex devices. Maintenance is often best left to qualified professionals, specifically the manufacturer or an approved third party. However, there are some basic maintenance duties that can be carried out locally which can prevent more complex issues from developing. VSDs must be kept clean, as dust on hardware can contribute to poor airflow and even short circuits. This can be alleviated by periodically spraying air through the heat sink fan. However, the air must be oil-free and contain no water. VSDs must also be kept dry to prevent moisture from getting in and causing corrosion on circuit boards. Keeping connections tight is also important, as heat cycles and mechanical vibrations can loosen them over time, which can potentially cause arcing. This, in turn, leads to nuisance overvoltage faults, clearing of input fuses, or damage to protective components.

Whole life approach

In the event of a complete failure, if a VSD cannot be repaired economically then it may be time to replace it. However, this is not a decision that should be taken lightly, and certainly not one you would ordinarily wish to rush. Choosing the right replacement VSDs under pressure, amid mounting production backlogs, can result in flawed decision-making or incorrect installation. It is far better to have a plan in place beforehand that can be activated so that downtime can be kept to a minimum, and the right VSD is selected for the right application.

This is best achieved by taking a whole life approach to the management of both maintenance and upgrades for all VSDs in operation, as well as spares. It considers ongoing maintenance requirements while also considering obsolescence, replacements and upgrades in the future. This can help to take the element of surprise out of having to replace a drive and allow potential failures to be anticipated more effectively.

Having the ability to catalogue the expected life cycle of a drive and put appropriate plans in place for each one in a fleet, saves time, cuts costs, and ultimately helps to improve profitability by ensuring that every part of a plant’s processes can continue running uninterrupted in the event of a failure. Overall total cost of ownership can be reduced by taking a strategic approach to replacement and upgrades, ensuring that VSDs approaching the end of their operational life are appropriately replaced before they risk failure, while embracing new drive technologies and functions as they emerge.

Approaching maintenance strategically

Implementing a comprehensive and ongoing review of the status of all VSDs at a given time can be difficult and time consuming, but services like ABB’s Life Cycle Assessment (LCA) are available to make it easier. ABB’s Andy Pearson says this tool essentially automates many aspects of the process, helping to provide a quick and easy way to establish a life cycle management strategy and an effective maintenance strategy for each drive individually and collectively. In ABB’s case, the service can cover both its drives and other major drive brands. VSDs are registered using information collected from the customer’s own fleet management systemin an online tool. Alternatively, this can be done with a site visit from an ABB engineer or one of its Value Provider partners, who can make the assessment for you. Once VSDs are registered, the tool provides a comprehensive overview of the life cycle state and operating conditions of each drive for better decision making and maintenance scheduling.

The LCA tool logs age, location, criticality, operating environment, service history and part replacement history. This allows maintenance to be tailored to the needs of each drive, while flagging any drives or components that need particular attention. Critical drives and at-risk assets are identified, providing a comprehensive overview of the entire infrastructure. The tool also highlights, in a report, those assets which need servicing or are candidates for replacement or upgrade. This helps avoid unplanned downtime and can be used to project maintenance budgets and manage costs. It can also help companies to modernise their operations by providing a schedule for replacing and upgrading equipment that might be approaching obsolescence. While the LCA tool targets VSDs, the impact of using smart sensors to track the health of motors can add to a 360-degree view of the overall powertrain performance. Smart sensors are applied to motors and can digitally feed near real-time performance and condition data back to plant operators. This helps companies to make informed decisions based on hard data and deploy maintenance teams where and when they are needed. Ultimately, it has never been easier to adopt a whole life approach to drive and motor maintenance management, helping to cut costs and reduce failures.