Using medium-voltage VFDs for better pump process control

How product innovations are revolutionizing pump monitoring and process control management.

By Rob Lax October 2, 2015

As rotating machines, especially pumps, have grown in power and size, the natural progression is to find more efficient and effective ways to monitor and control these critical process machines. Since medium-voltage (MV) variable frequency drives (VFD) have come a long way in just a few years, they have evolved into a more intuitive and powerful part of the process industry. With process pumps now working in high-energy applications, it takes a more robust design for the “heavy lifting” found in typical industrial processes.

Today’s MV drive for the process industries is an integrated process pump monitoring and control management system consisting of a modern, more efficient VFD, patented logic control, and advanced pump display. This innovation provides operational feedback about peak pump efficiency and overall system energy usage. Advances in MV pump controllers enable improved process control and increased visibility of pump operations. MV control and monitoring technology is a key component in a pump’s operation and prolongs its lifecycle. Many plant operators don’t realize they need a more intuitive MV controller until it is too late. If there is a potential problem with a high-energy pumping system, it is critical to know as much as possible about that pump, motor, and system before the alarms go off.

Improve pump system performance

By using VFD controls, plant operators have the ability to more accurately control the pump and impeller speed at a varied rate, allowing the pump/motor output to match the system requirement for improved pump performance based on varying load demands. These MV controls also allow the integration of logic and respond, when valves are opening or closing to bring on multiple system pumps to handle a variety of process demands. Ensuring your process pump is evenly balanced during minimum and maximum loads and keeping the pump close to Best Efficiency Point (BEP) will lead to the optimal pump performance. With the innovative capabilities of the MV pump process drive, pump operating systems are no longer inhibited by differing viscosities and pump pressures in the work environment. MV VFD controls are best used for heavy industry applications, including crude oil, metals, power generation, and medium- to large-size municipalities.

Monitor pump operation

MV drives offer expanded monitoring capabilities for industrial pump operations. Many vehicles are now able to self-monitor and alert the driver when there is an issue. Pump MVs now can streamline the process using instrumentation, VFD data, and patented algorithms to calculate and monitor critical pump operating parameters.

Solutions are available that detail the amps and speed of the process pump and provide real-time pump operation information such as flow, net positive suction head (NPSH) margin, BEP percentage, and actual operating point on the curve.

Typical inputs used by MV drives to model pump performance are pressure, temperature, torque, power, and speed. In the standard sensorless version, energy levels and the status of your pump can be calculated. Using suction and discharge pressure, advanced versions can calculate flow, total dynamic head (TDH), and NPSH. The MV technology is a necessary maintenance function, as many pump failures are process related.

Provide greater visibility

MV drives provide the ability to see what a pump is doing and its impact in a larger pump system operation. It’s important to find an MV that offers visibility above and beyond a standard VFD. Look especially for products that have large memory and data capacity. It’s wise to document as much data as possible to become better acquainted with your machinery and ensure its productivity. To view this data, seek units with large displays. Some models are as wide as 12 in. and provide real-time feedback on BEP percentage calculation, flow/power ratio, and energy savings calculations.

When searching for an MV solution, partner with a company that focuses strictly on pumps and pumping systems, including centrifugal pumps and twin screw-type pumps. This early choice will ensure that future maintenance work on your product is performed by a company who specializes in your machinery. Some manufacturers apply VFDs to other machines while others focus strictly on pumps and pumping systems.

Consider this: A large gas plant in northern Russia is currently using an MV VFD to better control and protect its pumps. The plant chose a globally recognized solutions provider to propose and install the new monitoring technology. Plant managers had recognized that their pumps were critical to plant operations and safety-any downtime in their systems would be costly to operations.

In these high-risk industries, a failure in the pump operations can cause a catastrophic failure for the whole plant. Pump operators need continual visibility so they can make decisions that are critical to maintaining operations. The solution proposed, and ultimately installed, for the gas plant was a 6,900 V, 800-kW MV drive with four BB5-type API multistage pumps. This controller provides pump operators with better visibility of their pumps, increasing their ability to monitor pump performance.

The increased visibility means pump operators can make better, more informed decisions about the critical operations of their systems. Today, the gas plant is operating successfully thanks to their new technology.

Considering safety

Workplace safety is a major concern and top priority for any plant and its employees. MV drives are equipped with multiple high-voltage components and require specific sizing and insulation. More components require a higher precaution for safety. In North America, regulations from OSHA and NFPA must be met with this type of machinery. In other parts of the world, similar agencies monitor and regulate this type of equipment safety. It is important to find MVs that come with safety manuals and companies that provide hands-on training so that plant workers can become familiar with the technology.

Please note that special safety considerations are necessary for people in close proximity to an MV VFD. To ensure the safety of all plant employees, these types of products require installation and training by specialized professionals.

Price vs. value of product

As with any large capital machinery purchase, there are multiple considerations to take into account while weighing the best decision for your plant process operation. What comes to mind first for many plant managers is cost and return on investment (ROI). Depending on what features the MV VFD offers, there may be an opportunity to save on energy costs when purchasing an MV drive, leading to increased ROI. If energy savings is not high on the list, it is important to make sure to include the cost of extended warranties and process guarantees when evaluating. Look for companies that offer extended warranties in cases when a pump and the MV are purchased together. Companies can also offer increased pump protection, global site support, and aftermarket support with the purchase of an entire MV pumping system. Be sure to consider all options to make sure the product you’re purchasing comes with the additions needed to maximize pump life and efficiency.

Before making any investment in vibration and temperature controls, keep in mind that a majority of pump problems occur on the process side. Consider allocating plant funds toward an MV VFD guarantee and warranty so the pump can maintain itself with VFD technology, ensuring less downtime and avoiding unexpected aftermarket costs and costly repairs. The price of an MV and its value are two different aspects, and each should be considered. Price and value of the MV are two different aspects the buyer should be aware of, as they are distinctly different. The lowest price is not always the best choice when providing this type of important equipment.

It often is a significant investment to purchase a plant’s most important pump machinery, but in the long run, including a more intelligent MV drive can usually optimize the pump’s performance and lifecycle.

Pump monitoring and control management is no longer a guessing game with the introduction of the advanced pump display on MV VFDs. Giants in the natural gas industry, and many others, are already relying on this technology to help them control and monitor their pumps safely and effectively. As control innovation moves forward, a natural progression is to provide monitoring displays that share all aspects of the pump’s performance and energy use.

Investing in this type of equipment requires multiple considerations regarding initial capital cost, ROI, support, equipment warranty, and process guarantees. Choosing the right MV VFD for a higher-energy pumping system can enhance a plant’s overall operational efficiency rates, increase pump lifecycles, decrease unplanned repairs, enhance overall plant safety, and decrease plant downtime.

Rob Lax is global product manager for PumpSmart control technologies for ITT.