Drives / Motors

Motors, drives deliver force behind the scenes

Hardworking rotating devices are getting help from variable-speed devices, efficiency rules, and onboard and networked intelligence to aid process applications worldwide.

By Jim Montague

Because fluids are universally heavy and process applications are usually in harsh, remote and/or weather-beaten settings, the motors and drives that serve them typically have a tougher time than their counterparts elsewhere—requiring them to be stronger, more durable and more reliable. And yet, they don't seem to get much credit. A lot of rotating equipment in process applications often seems to be treated as a support-role afterthought by their users and organizations—only coming to mind when they trip or fails and stops production. 

"The process industries continue to be ruled by automation equipment such as PLCs and DCSs, so I think motors and drives are still viewed like I/O points," says Richard Kirkpatrick, project manager for variable speed (VS) AC motors at Baldor Electric Co., an ABB Group member.

In recent years, most advances in motors and drives concentrated on increasing efficiency, adopting variable speed/frequency drives (VSD/VFD), adding permanent magnets to increase power density, integrating regenerative functions to save power, and adding intelligence onboard or nearby to achieve further operational gains. But, as producers say in Hollywood, "What have they done for us lately?" Well, if they weren't so strong and silent, and were more visible, the answer would be "plenty."

"The process control industry traditionally focuses on operational improvements that driving out variability and push constraints to make money. However, you can still make product when a PID loop is under performing by putting the loop in manual. You can't make product when your rotating equipment goes down," says Tim Shope, industry and process consulting manager for North America at Rockwell Automation (www.rockwellautomation.com). "In addition to smart instrumentation and final control elements, we're seeing a trend towards asset management of electrical devices inside the control narrative."

Skip trucks in the desert

At their most basic, motors and drives have made much of the modern world possible in the close to 200 years following the first Industrial Revolution, but their labor-saving capabilities are still taking over for manual and other less-efficient forms of work in many expanded applications and in remote and developing regions.       

For instance, the Kapurdi lignite mine in northwest India was established in 2010 to deliver brown coal to the Jallipa Kapurdi coal-fired power plant, which are both owned by the Barmer Lignite Mining Co., Ltd. The lignite was initially transported 4.5 km from the mine to the plant in trucks, but after two years, BLMCL determined that a conveyor would be more efficient, according to senior VP Anil Sood. "Transporting the lignite on a conveyor is more environmentally friendly with minimal pollution and dust,” says Sood. “A conveyor was also a more cost-effective, all-weather solution.”

White paper: 13 common causes of motor failure 

Because the lignite conveyor would be the power plant's lifeline and one of India's longest, it was vital for it to have reliable motors, drives and controls. BLMCL eventually decided to use three Dodge controlled start transmission (CST) units from ABB. "The CST design combines a planetary gear reducer with an integral wet clutch system to provide an efficient transmission of motor power and torque,” says Prabal Bose, ABB’s regional sales manager for Dodge MPT in India. “This allows consistent, smooth startup and shutdown of long conveyor belts, which adds to the reliability of the entire system by minimizing peak loads and stresses on all  conveyor components. Its double-lip taconite sealing system with added excluder seal prevents any contamination from entering the CST.” 

Sood reports that BLMCL thought CST might be the best option its desert location with high temperatures and dust, and that it's delivered several years of trouble-free performance. "We've been operating the mine at 100% capacity for more than two and a half years,” explains Sood. “The CST drives have delivered 99% availability with no breakdowns, and have only required oil replacement."

Located in another desert, the Nakhla gas-oil separation plant (GOSP) in Libya is operated by BASF subsidiary Wintershall Holding GmbH in Kassel, Germany, which recently switched from a diesel-driven power plant to a 7-MW gas turbine with a 10.2-MVA, synchronous generator weighing 36 tonnes, and matching instrumentation and controls from WEG Group (www.weg.net). The result is an autonomous unit that uses associated gas from the GOSP to reduce environmental impact and increase plant availability, which was needed after the introduction of a water injection process. The plant previously needed 40,000 liters per week of diesel fuel per week to run its separation process, and that fuel had to be trucked in, which was costly and risky. The new generator took about a year to build, and has already run 20,000 hours in continuous service.

One of the generator's customized features is air cooling with a top-mounted air/air heat exchanger and external fans. The air filter prevents sand accumulation with all sand particles fed out through slits. Also, the four-pole generator with IP55 protection rating is designed for 6,000 V at 50 Hz and up to 55 °C, and is painted white to minimize heat absorption. In addition, a 30-kV overhead line connecting Nakhla to the diesel power plant at the Hamid site provides power supply redundancy. The GOSP can now be operated from the gas turbine/generator or from the diesel power plant in case of emergency. Finally, 14 MW of surplus heat from the gas turbine is now used to heat extracted, crude oil up to 70 °C instead of using five hot-water boilers.

“High operational reliability and availability were our main concerns when selecting the generator,” explains Rainer Bleich, project manager at Wintershall. “Electricity generation is vital for continuous operation of our GOSP in Nakhla because every day of downtime can cost us millions of euros. Also, lead time for this kind of custom generator can be as much as 18 months from design to commissioning, and it takes at least two to three days for external fitters to reach the site if repairs are needed.”   

Since switching to its new turbine/generator, Wintershall has gained several benefits, including better operational security along with reliable, autonomous and redundant electricity. It reports the new generating system requires much less maintenance than the previous diesel plant, and trucking in fuel is only needed in an emergency. This has reduced diesel consumption, leading to cost savings and reduced CO2 emissions.

Speed control still saves

Though many innovations in motors and drives are newer and maybe more attractive, nothing has delivered more efficiency gains than the continuing expansion of VSDs and VFDs in process control applications and in manufacturing in general.

"It's generally agreed that we can expect power consumption to increase 42% over the next 20 years due to growing populations and increasing use of motors and drives for pumps, fans and other uses, and VSDs can help with those costs," says Rockwell's Shope. "However, it's important to remember that the total ownership cost (TOC) for rotating assets typically consists of just 10% for the initial cost of buying the motor, VSD, starter, pump, etc. and another 15% for maintenance, while the remaining 70-80% is energy costs. That's the big one that VSDs can help with."

Harvey Eure, VFD and power quality product manager, Delta Products Corp., adds that, "Low-voltage VFDs operate AC motors that are typically 5 hp and above to reduce electricity costs, control process speed, and reduce wear and tear of mechanical systems such as conveyors or pumps linked to the AC motor. However, there's been a trend of using VFDs more frequently in smaller motor applications with fractional horsepower—about 0.25 hp and up—for AC induction and permanent magnet motors. In addition, VFD costs have declined in recent years, making them more affordable for smaller AC motor applications such as factory automation equipment and small conveyors.   Compared to traditional gearboxes, VFDs provide more precise control of motor speed and process speed.

"For larger AC motors, the trend is using VFDs with active front-end sections to lower harmonics and regenerate electricity. In applications with high inductive loads, such as water pump motors, users monitor the facility's electrical system harmonics that's generated back to the power utility from non-linear load sources such as VFDs. The diode rectifier, along with capacitors charging and discharging, create non-sinusoidal voltage and current waveforms back to the power utility grid.  Because utilities can charge penalties to facilities with poor power quality, and to prevent this in the future, facilities with large motors will begin buying VFDs with active front ends for lower harmonics."

Eure adds that Delta has developed a VFD panel for oil and gas pumps, which employs a VFD with a reciprocating piston pump for an oil well. "The pump mechanically lifts liquid from an oil well, while the panel increases production time by varying the speed according to the fluid level with a user-defined stroke-per-minute command," he explains. "The control scheme has been adapted to a variety of oil and gas pump systems to optimize pumping speed and save on energy. 

"The VFD provides four-quadrant control with regenerative energy fed to the active front end device. Electrical energy is regenerated back to the utility during the pump-down stroke, which accounts for 50% of the pump rod motion. The regenerative VFD minimizes wear and tear on mechanical components, such as the rod strings, gearboxes and v-belts due to reduced pump starting and stopping."

Jason Hoover, business development director, Siemens, adds that, "There are many different topologies for taking in three-phase power and turning it into the motion and force delivered by motors and drives. We all know about VFDs, including our Sinamics Perfect Harmony GH150 medium-voltage drive with Sinamics Modular Multilevel Converter (M2C) with more efficient speed control and a more modular topology.

"However, the big issue now isn't just technology, but how users are choosing to maintain motors and drives with help from the Industrial Internet of Things (IIoT) to help take reliability and availability to the next level. We've added sensors to our motors and drives, so users can better employ minimally invasive IoT technology to better see and maintain the health of their costly assets. Likewise, our Drive Train Analytics program was launched with Perfect Harmony in 2014, and it lets us log in and monitor motors and drives for our subscribers, give them dashboard and status updates, and coach them on keeping them up and running."   

Standards assist as well

Because of the operational and financial benefits they deliver, variable-speed and other efficiency-boosting technologies have also been supported and advocated by many standards organizations and regulatory bodies in recent years. 

"Standards keep evolving, and energy-efficiency laws like the Energy Policy Act (EPAct) in 1999 and the Energy Independence and Security Act in 2007, have been followed by the U.S. Dept. of Energy's more recent U.S. Integral HP Motor Rule in 2016," says Baldor's Kirkpatrick. "Meanwhile, the process industries have always made significant use of VS motors, and until now they've been exempt from most efficiency rules because they can achieve some percentage gains just by decreasing their speeds. However, there's now talk that the EU's European Commission may soon draft efficiency rules for overall systems that include VS motors and drives, and those requirements will likely hit us, too."

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Smart design expands flexibility

Just as with most other process control devices, motors and drives have also added onboard data processing and intelligence for more flexible performance across voltage levels and more proactive maintenance.

While it may once have seemed impossible to control a medium-voltage AC motor with a low-voltage AC drive, 100-year-old Ash Grove Cement in Chanute, Kan., recently implemented a low-voltage, AC VFD with its existing, 2,300-hp, medium-voltage AC motors to solve problems with  its old motor controls (Figure 1). To maximize production, the Chanute plant continuously manufactures cement, using almost 1,000 motors that generate a combined 45,000 hp to produce five tons of cement per minute, but its former control system was unreliable and required constant maintenance.

“The success or failure of our plant depends on our motors. We need reliable equipment and ongoing maintenance to protect our motors, control production and operate efficiently,” says Bob Wright, electric operations manager at Ash Grove. "Not long ago, manufacturers had a run-until-it-breaks mentality, but now we have the tools to protect more capital investments like our motors.”

In addition, staff at the Chanute plant were having trouble using a 60-hp generator motor to manually rotate and position their three ball mills for monthly servicing, which further limited production and revenue. “Each hour that we stop operations to perform maintenance or resolve a fault translates to 300 tons of cement that could have been produced,” Wright explained. "Usually, this situation called for a new spotting controller and gear motor or a medium-voltage drive.”

Instead, Ash Grove replaced generators powering the mill's spotter with preconfigured, 480-V, 450-hp Allen-Bradley AC VFDs from Rockwell Automation. These drives power three existing 4,000-V, 2,300-hp AC motors exclusively during spotting to rotate the ball mill efficiently, and bring it to controlled starts and stops. Also, the low-voltage AC drive has the torque control to operate at the 6 Hz the ball mill requires for spotting. The drive can separate and independently control motor flux and torque-producing current, allowing it to deliver full torque down to zero speed. These capabilities, coupled with precise motor speed control, allow the AC drive to handle demanding motor control applications, including applications typically reserved for DC motors.

By networking it new drive to an existing Allen-Bradley ControlLogix PAC, Ash Grove improved operational performance, receives real-time access to crucial production data, and protects assets with advanced diagnostic and protection capabilities. Unlike the previous generator, smooth VFD technology reduces equipment wear, as well as time and money previously spent on maintaining the motor. Instead of needing annual motor maintenance, the new AC drive also requires less upkeep and motor rewinding. As a result, Ash Grove not only updated its drives, it modernized its approach to maintaining capital investments, saved an initial $250,000, and achieved 90% uptime.

“Besides costing less than half as much as a medium voltage drive, using a low-voltage AC drive in this application saves on maintenance and energy,” Wright said. "We believe in maintaining motors for the long run. It saves us more money to dedicate our efforts toward protecting these motors instead of running them until they break. In the past, we ran the generator's motor during the spotting process. Unlike the generator, the VFD consumes much less power while we service the mills, which means more energy savings.”

On the fan side, Gunjang Energy Co., Ltd. in Gansan, Jella-buk-do, southern province, South Korea, reports it recently sought to completely automate a fan application without shutting down its steam-heat facility, and maintain stable, reliable operations at the same time. The plant provides affordable, high-quality, processed steam to 19 commercial customers in the nearby Gunsan Regional Industrial Complex and one in the Chungnam Janghang area, who have reduced their fuel costs by an average of 36% for eight years compared to traditional power sources. Gunjang also reduced air pollutants, such as NOx, Sox and dust, by about 29% by integrating more than 20 burners and combustion systems across client sites, and jointly managing their chimneys as one system. 

To improve energy utilization and achieve a two-year return on investment (ROI) by establishing consistent cost savings in the face of rising energy costs, Gunjang reports it decided to upgrade core components and encourage similar efforts in other locations, rather than commit to a full migration that would be complex and time-consuming. Consequently, where the steam utility previously used dampers to control airflow, it now opted to achieve more consistency and efficiency by adopting PowerFlex 7000 medium-voltage drives from Rockwell Automation on three induced draft (ID) fans to maintain designated temperature and airflow of the boiler. After the drive panel and controls were commissioned by local Rockwell Automation distributor Autocon, Gunjang reports it saved $682,000, cut its ROI to just one year, and is expected to generate average savings of $1.76 million per year.

Baldor's Kirkpatrick adds that, "We're also beginning to see direct-drive solutions without gearboxes because if users can get the added torque they need with permanent magnets or other more power-dense designs, then they can eliminate gearboxes, which have relatively higher maintenance, more reliability failure points, and efficiency that degrades sooner over time. Similarly, laminated-frame designs—with laminated steel plates in the stator serving as the motor frame—used to be only in servomotors, but they've been making their way into larger motors in recent years. This design provides better heat dissipation and increases power density at the same time."

Future sensing, analysis

Inevitably, as more motors and drives get connected to more networks and data processing systems, the resulting analytics will drive new levels of optimization. 

To monitor these innovations and the motors they're in, Kirkpatrick reports that ABB has created a battery-powered Smart Sensor for preventive maintenance on low-voltage motors as part of its ABBAbility program. "Smart Sensor pulls vibration, temperature and other data, communicates via WiFi or Bluetooth, and is designed to work with almost any motor," he adds. "We're also working to integrate IIoT into drives, and all these concepts are integrating into smaller, self-contained devices that are more intelligent and connected via wireless."

Rockwell Automation's Shope adds, "The question is how can process applications continue to identify sources of variability to do predictive maintenance, whether they can use vibration analysis, acoustics or in-device diagnostics, and how can they combine or coordinate those data sources? For instance, our IntelliCenter motor control center (MCC) devices and software have been equipped with Ethernet for about six years, and users have taken infrared (IR) cameras to check for hotspots, but I envision a day when IR sensors will be embedded with motor starter to do continuous monitoring.

"Overall, we can get a lot more data today than we could 20 years ago, and we can find performance degradations at the same time as we decouple the electrical from the mechanical sides of an application. This could be done in the past, but it was manual and time-consuming. Now we can build models  and digital twins that tie everything together for assets such as motors and pumps to make monitoring and efficiency improvements even more proactive. For example, as part of integrating with our PlantPAx system, pre-configured devices can add functions from our Library of Process Objects, and communicate directly via EtherNet/IP with drives or relays. As a result, where drive faults were often hard to find previously, operators can now do fault-code look-ups that display them in contextual format. This reduces mean time to repair (MTTR), and empowers operators to be front-line troubleshooters. In the future, predictive analytics and big data will detect optimal performance earlier, and drive even more inefficiency out of processes with motors and drives."