Motors, Drives

Low-priced medium-voltage drives can have long-term costs

Consider how reliability and performance impact total cost of ownership (TCO) when buying or specifying medium-voltage drives rather than focus only on the initial price point.
By Pat Lemmon April 3, 2019
Courtesy: Intermountain Electronics

Medium-voltage drives are one of the most process-critical pieces of equipment in heavy industrial operations. Given the high downtime costs in large-scale operations, most companies can’t afford for drives to go down for even an hour. However, drive reliability has become a challenge for many operations as purchasing priorities have changed. Companies trying to stretch capital further are opting for cheaper drives, putting their long-term business goals at risk as a result.

Changing buying priorities

Historically, industrial companies purposely bought medium-voltage drives that would reliably last up to 20 years. But many companies tightened their budgets after the global economic downturn. This has led them (or the EPC working on their behalf) to place a higher priority on a drive’s up-front cost than its long-term performance.

Some drive suppliers have noted these new priorities and are using cheaper, lower-quality components to offer less-expensive drive options. However, this sacrifice in product quality can come at the expense of performance and reliability for end users.

For example, some suppliers now use aluminum instead of copper in drive transformers. This cuts the cost of a drive, but results in less efficient transformers. An end user will pay more in energy costs over the drive’s lifetime than what they saved on the initial cost.

Lower-quality drives, which are more likely to fail, also will be more expensive to maintain over their lifetime. And their life span may only be a period of years instead of decades.

What to look for when buying or specifying a drive

Rather than specifying or buying a medium-voltage drive purely based on up-front price, consider its total cost of ownership (TCO). This requires evaluating a drive’s performance and reliability and how it can deliver cost savings in areas such as integration into the control system and risk management.

Performance and reliability

Users need to ask how long a medium-voltage drive will reliably operate. If the answer is 20 years, specify that in the procurement process. Some suppliers can deliver drives with upward of 100,000 hours of mean time between failure (MTBF), which is more than 20 years in a typical operation. Other suppliers only offer drives with a fraction of that MTBF. What may seem like a lower cost drive today will be much costlier down the road if the drive is replaced in five years instead of 20 years.

Likewise, consider how a drive’s design can impact operating costs. Going back to the transformer example, the use of aluminum may be 5% less efficient than copper. That seems small, but lower efficiency can cost more than the initial purchase price in additional energy costs over a drive’s life span.

If redundancy is important, consider using a drive with bypass options. In the event of a critical component failure, the drive can bypass the component to keep the drive running. This can provide a user a window to plan for a scheduled shutdown.

Quick start savings

A medium-voltage drive can start paying dividends faster if users can minimize the time it takes to get it up and running in a plant.

For example, manually integrating and configuring devices and systems can be a time-consuming and labor-intensive process, so drives that have control systems with built-in advanced integration can reduce development and configuration time.

With advanced integration, a controller can recognize certain devices and automatically import their add-on profiles. Mapping devices becomes easier because an engineer no longer needs to manually associate parameter numbers with descriptions or enter a device’s details. The ability to use one development environment can reduce the potential for development and input/output-mismatch errors.

A drive that supports remote monitoring allows a vendor to monitor its performance. The vendor can notify of any faults, warnings or performance outside of a defined tolerance. Image shows the Allen-Bradley PowerFlex 6000 medium-voltage ac drives from Rockwell Automation, which allow for flexibility in a variety of applications, new and retrofit, variable torque, and constant torque. Courtesy: Intermountain Electronics

A drive that supports remote monitoring allows a vendor to monitor its performance. The vendor can notify of any faults, warnings or performance outside of a defined tolerance. Image shows the Allen-Bradley PowerFlex 6000 medium-voltage ac drives from Rockwell Automation, which allow for flexibility in a variety of applications, new and retrofit, variable torque, and constant torque. Courtesy: Intermountain Electronics

A system integrator with the right application expertise can maximize these efficiencies to integrate the controller with the medium-voltage drive, human interfaces, and remote monitoring for all the connected site applications.

Some drives also come with add-on instructions (AOIs), which are reusable code objects. AOIs are defined once in a controller project and can be reused multiple times. This helps commission systems faster and promotes greater programming consistency across a plant’s operations.

Finally, different drive vendors offer varied factory acceptance testing (FAT) levels. A vendor that tests the drive at full voltage and power can give the user greater confidence the drive will perform as expected, before it arrives at the facility.

Risk management

A medium-voltage drive can help better manage the risks and costs of potential safety, security and downtime incidents.

Safety: Arc-resistant drives can help users meet stringent global arc-resistance standards. These drives redirect hazardous energy and gases created from arc-flash events away from personnel. This reduces safety risks as well as protects equipment.

Drives also can use safe torque off (STO) technology to remove power from a motor without removing power to the drive. This is critical to reduce cycle times for batch process applications and can help achieve a faster system restart after a safe state is reached. STO is designed into the drive control and doesn’t require additional electromechanical components, which can help lower hardware, inventory and installation costs.

Security: Drives, like all aspects of industrial operations, are increasingly connected. With this greater connectivity comes greater potential for security risks. If the drive offers remote monitoring and data collection capabilities, make sure it offers secure connectivity features such as a secure socket layer through a standard Internet connection.

Downtime: In addition to specifying or purchasing reliable drives to prevent downtime in the first place, different levels of support can help monitor and maintain the drives.

For example, a drive that supports remote monitoring allows a vendor to monitor its performance. The vendor immediately notifies the user of any faults, warnings or performance outside of a defined tolerance. Advances are being made to design in predictive analytics to forecast device health and proactively schedule maintenance. This helps a user identify and respond to any issues to reduce or avoid downtime completely. It can also offset skills-shortage challenges by tasking drive monitoring to a trusted vendor.

Protect your operations

Medium-voltage drives should help facilitate a company’s operations and business goals,. When specifying drives, look beyond the sticker price to understand lifecycle costs in key areas like downtime, energy usage, system integration, and risk management.

Pat Lemmon, director of technical support, Intermountain Electronics. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, cvavra@cfemedia.com.

MORE ANSWERS

Keywords: medium-voltage drives, energy efficiency, risk management

Companies should think long term when choosing a medium-voltage motor for their operations.

Cheaper motors can have long-term added costs for a company due to inferior materials and construction.

Medium-voltage drives should facilitate a company’s operations and business goals and provide long-term savings through the motor’s life.

Consider this

What other considerations should a company have when selecting and purchasing a medium-voltage drive?


Pat Lemmon
Author Bio: Pat Lemmon, director of technical support, Intermountain Electronics.