Electrical Insulation Magazine — Jul/Aug 2021

Howard W. Penrose, PhD, CMRP

President, MotorDoc® LLC

From Green Coils to a Green Economy

As global focus turns to the green economy, the challenges that are presented to manufacturers of rotating machinery and insulation material can be daunting. The application of traditional standards and materials to the new applications and rotating machinery designs will, and have, resulted in serious equipment reliability and monitoring problems. A whole new approach is required for practical applications and the use of those standards in everything from smart grid energy storage, hybrid-electric vehicles to Internet of Things (IoT) devices, and sensors to data interpretation.

When the average person is exposed to media reports about zero emissions and the elimination of fossil fuels, they rarely consider the challenges. From the rotating machinery and materials perspective, it can be exciting as new materials, applications, and aging systems develop, especially as the global focus is on the electrification of almost everything. What is the next generation of insulating materials if we lose access to oil? How do we process the materials? What are the impacts? How do we test them?What is the transition?

Right now, we are managing the impacts of traditional manufacturing and repair techniques in generators, transformers, cabling, and other electrical systems in wind power. As noted over the past decade, small deviations in slot wedges and coil design and stator manufacturing have significant effects on the reliability of wind generation. What would pass on a constant-load, ground-based generator has serious implications when the rotating machine is high on a platform with frequent starts and stops and rapidly varying load conditions.The effects of tolerances and thermal cycling becomes critical in large machines that are manufactured to be as cost effective as possible.

When we look to transportation and heavy equipment electrification, the design engineer must consider how the human operator will manage the system. What limitations must be put on a hybrid or electric vehicle to reduce the chaos associated with varying driver styles in order to achieve the perceived reliability of that vehicle on the market? What is the effect of the cooling medium, such as transmission fluid,especially as it ages and carries other contaminants? Although this may become a simpler issue as vehicles move toward driverless, the acceptance of the newer technologies by the public will determine how quickly we move in that direction.

Sensors and prognostics are also accelerating as machine learning and augmented intelligence (AI) techniques continue to advance.Challenges range from ethical use of AI to the reliability of the sensors themselves and how the data are managed. The effects of a faulty sensor, a defect in programming, or even cyber security failures must be considered as all these advances become more automated and connected. The engineer involved in the design of new or modification of existing rotating machinery systems must now understand the effect of connected faults in a far more complex system and consider the new term“resilience.”

Present State

As the renewable energy portfolio continues to expand in the areas of new technologies such as wind, solar, tidal, geo-thermal, battery storage, flywheel storage, and fuel cells and older technologies, the effects on transmission and distribution systems have increased. While new standards, agreements,and smart grid frameworks are being developed, the effect on existing systems is becoming apparent. At the local level, in such locations as wind farms, oil-filled and dry transformer failures are occurring well above the expected failure rates, as are failures in cable splices and generator components such as coils, wedges, and connections. On the larger scale, as electrification increases, regions struggle with meeting demand, and some systems are operating at peak capacity, leaving the systems vulnerable to weather and equipment failures. The component failures range from legacy systems being exposed to new aging systems and unplanned weather exposures to newer systems made from materials with shorter life-cycles. Maintenance and monitoring techniques have also evolved in an environment where cost reductions are a goal. Some Of the changes have been improvements, such as new monitoring systems, and some have been excessive and have had disastrous results, as have been noted since 2003 in the USA alone. As we add additional electrification, such as with electric vehicle charging stations, the effects on transmission, distribution, and generation will continue to increase even as smart grid and smart charging systems develop.

Starting back with deregulation in the 1990s, in the USA, the power-generation landscape changed drastically. From the larger base-loaded plants with spinning reserves, we have moved to a more distributed network of peaking plants and energy storage systems. A natural gas plant, solar or wind farm, geo-thermal facility, or hydro plant can come online from a cold stop far faster than a coal-fired plant or nuclear power. With varying load requirements, the larger coal-fired plants are brought on and removed from production more than in the past, with load variations designed to match customer needs. Although the older plants are operating outside of their original design context, the newer types of facilities are operating with equipment and machines designed with the same standards used to develop the older rotating machines and transformers. The problems become more complex when you add in newer material technology in which limited application experience exists, especially in a variable-demand environment, coupled with the effects of power and home electronics on power quality and homeowners and businesses becoming power producers.

Because wind power is one of the larger utility-scale renewable technologies, and a significant area of material and reliability research, it should receive a little extra consideration. The materials that make up the blades,generator, controls, cabling, and transformers all require attention, with the blades beingsubjected to direct environmental conditions such as weather and location. While off-shore and on-shore wind power have some specific differences, there are some definite similarities. These include wedge issues in the stators and DFIG (doubly fed induction generators) rotors, connections, and coils, which are normally form wound. The ambient conditions are global to the components because the machine is suspended in air, resulting in more drastic thermal cycling with load changes and outages driven by power demand and wind conditions. This affects rotor connections as well as components such as magnetic wedges that are not keyed properly and coil fits in the slots, which can result in grounds. Depending on the design, these three conditions will often rank in the top five reasons for extended turbine outages, with blades and gearbox failures also ranking near the top.

Transportation is having a significant impact as plug-in hybrid-electric and electric vehicles increase in market share, in addition to fuel-saving techniques built into other personal vehicles. For instance, with the use of the autostop function for in-town driving, where a vehicle’s engine turns off at stops (traffic lights and stopped traffic), most of the previous engine and belt-drive components are now electric motor driven. The traction motors in hybrid and electric vehicles vary in type but are generally cooled with transmission fluid and are usually developed as motor generators with permanent magnet rotors. Theinsulation systems used in these technologies are not much different from those used in other commercial or industrial applications but are subjected to rapid changes in operating temperature and load, depending on driving conditions and the operator. Improvements in materials are often implemented, such as the increase in nano-dielectric materials and other specialty wire insulation systems.

The most severe mobile equipment application is hybrid-electric construction machinery with more constant changing loads and variable operation. The studies associated with the insulation system for one large loader with two generators and four switched reluctance machines went about two years. The reliability goals generated completely new materials testing techniques with the goal of accurately determining risk of failure within specific parameters and length of time. Resulting improvements had significant effects on the rotating machine manufacturer’s original designs and material selection. As this sector grows, opportunities for improved insulation material design will be critical, for chemical resistance and thermal aging.

Commercial and industrial electric machines are experiencing changes in design and materials applications. The US Department of Energy has been funding novel approaches to electric machine designs for higher efficiencies including high-speed and high-horsepower compressor motors to reduce powertrain losses. Smaller smart motors are being developed with variable frequency drives being built into the motor frame, with several European fan manufacturers moving from induction motors to brushless DC. A significant consideration in every case is the power quality changes in most facilities as electronics from personal computers to IoT sensors and systems are installed.The need to understand the effect of True Power Factor, in addition to the harmonic conditions and related heating, on the electrical insulation system is second only to the effect of ground“noise” on the insulation systems. Fast-rise-time faults on across-the-line machines that are seeing impulses in the ground system from nearby large variable frequency drives have been confounding technicians at a growing rate.

Possible Future State

Advances in insulating material sciences and research appear to be rising to the challenge. New concepts in self-healing and self-diagnostic systems are in various stages of research and development due to investments in hybrid technology and green-economy rotating machinery and the distribution systems that support them. As we look to a carbon-neutral future, greater political and public pressure will be put on research and development to identify solutions to the electrification of the economy. For rotating machinery there are several directions of research from MEMS (microelectromechanical systems) sensors to materials self-sensoring and new testing technologies to older technologies being applied in new ways.

Although some discuss self-maintaining and self-repairing technologies, tradespeople are working with decades old technology for the prognostics and quality control of in-place and manufacturing process equipment. The challenges relate to the application of these technologies, and their advancement, through the life-cycle of rotating machinery in new environments. For the growing number of smaller electric machines (<700 volts), which include wind turbine generators, traditional testing, such as vibration analysis, has yielded troublingly few findings prior to failure. Older testing methodologies, such as electrical signature analysis, have yielded greater prognostics than expected once they are viewed in a new way. For larger machines (>1,000 volts), the situation is similar in that the noisier environment during operation and the application of traditional technologies becomes more challenging by system. In all cases, offline testing will need to be tailored to the potential operating environment, including the power supply and grounding system.Overall, the ability for AI to assist reliability engineers in modeling and trending a specific machine location and its operation will be critical in providing remaining useful life, or time-to-failure, estimation.

For the rotating machinery and insulating materials industry, the future is electrifying.Although standard technologies will continue, the general trend is toward specialized technologies for many new applications. This means a broader base of rotating machine technologies, the need for faster manufacturing of those technologies, rapid repair turnaround, and earlier fault detection will be required.