Motion System Design
Full speed ahead for motor technology

Full speed ahead for motor technology

During the next twenty years, motors will undergo dramatic changes and will look, function, and operate very differently from those built today

Put a motor built in 1978 next to a motor built in 1998 and there are more similarities than differences. But a motor built in 2018 will be radically different from one built today. Much of the change will stem from integrating the power components and information systems into the motor.

Integrated motor-drive packages are the first in a number of unfolding technologies that will launch the next motor development cycle. Others like active magnetic bearings, process monitoring intelligent motors, superconducting motors, and high-speed motors will revolutionize not only how motors are used, but their role in industrial automation.

Making the connection

Already, you can see evidence of the coming changes as more manufacturers combine gearbox, I/O, and switch gear with an integrated motor and drive system. By integrating an adjustable-speed drive into the motor, engineers can:

• Eliminate panel space for the ac drive.
• Eliminate wiring between the drive and the motor.
• Eliminate risk of reflective wave effects associated with PWM inverters.
• Obtain obvious single-source drive and motor responsibility.
• Save on installation and setup costs.

And, the motors and drives are tested together, with the motor’s parameters set at the factory to match with the drive.

Such benefits are converting engineers from fixed-speed (sine wave) operation to adjustablespeed operation. In addition, they find that their processes use less energy and have better process yields. Running at an optimum speed with fans and pumps, for example, reduces energy consumption and operating costs. The fans last longer and emit less noise. Pumps operating at optimum speed have less seal and bearing wear, which reduces maintenance needs and expense, and increases the pump’s capacity without spending more money.

Because of the smooth acceleration provided by adjustable-speed startup, belts last longer, reducing maintenance. And adjustablespeed eliminates the guesswork involved with selecting different sheave sizes when designing fan applications for the correct speed.

Although integrated motor and drive products are available now in ac and dc designs, they are limited to 10 hp and below. But this won’t last. Already in the works are integrated motor-drive packages with better network communications, expanded parameter and software setup capabilities, including operator interface modules, and higher horsepower frames. Developers are also working on increasing these products’ ability to withstand harsh environments, such as explosion- proof or wash down duty.

Signs of intelligence

There is also evidence of emerging intelligence in motors as information processing technology is added to the motor-drive package. Information systems with sensors integrated with on-board microprocessors monitor motor operation and analyze data from those sensors.

In addition to sensor processing, modeling and analysis capabilities are emerging in some motors. Sensory processing enables a system to compare sensory inputs to detect and recognize circumstances and events. Modeling and analysis capabilities enable the system to compile a best estimate of the state of the environment, retain information in memory (data base), and provide simulation and scenario impact analyses.

The sensors monitor such motor variables as:

• Current and voltage.
• Winding temperature.
• Bearing temperature and lubrication level.
• Shaft misalignment.
• Vibration.
• Speed in variable-speed applications.
• Torque.
• Rotor conditions.

The microprocessors and sensors monitor and analyze these on demand, providing reliable early warning of potential motor failure. Designers select and control the parameter thresholds for alert and fault conditions, ensuring such information is immediately available.

To communicate this information, these emerging intelligent motors use industry-standard protocols such as RS232 or DeviceNet. Data can also be sent to software packages such as Matlab and Excel for maintenance and trending.

Through such communication systems, operators can download new analysis and diagnostic algorithms from the Internet or host computers. Algorithms address such motor characteristics as:

• Ball passing frequencies of the bearing.
• Bar passing frequencies of the rotor.
• Stator slots configuration.
• Friction and windage losses.
• Natural resonance frequency.
• Winding and rotor thermal capability.

Present versions of intelligent motors operate in variable-speed applications, but with some limitations. They monitor vibration, bearing temperature, and winding temperature. They can also provide speed data if the motor has an encoder. However, diagnostic algorithms based on variable-speed current signatures are not yet available.

From these developments, engineers are already changing the way they view motors. As researchers develop better algorithms, intelligent motors will supplement and enhance the capability of the plant diagnostics expert. The information system of the motor will monitor and analyze the entire process, not just the motor.

No limits on speed

Active magnetic-bearing motor technology, though only in operation at a few sites, promises new levels of efficiency and service life for motor applications. An active magnetic bearing supports the motor’s shaft in a magnetic field. Electromagnets are arranged in a ring around the shaft’s journal and mounted in the motor housing. The main advantage is non-contact shaft support. Because the shaft is free-floating, controlled by the flux density of the electromagnets, there is no friction within the motor. This means that the motor has no speed limitations, can operate at higher than normal bearing temperatures, and that bearing lubrication is never necessary. In addition, there’s less bearing noise, and rotor balancing is automatic.

Engineers can control each electromagnet separately. They can tune the orbit of the shaft in its rotation and thereby control vibration.

The control scheme determines the motor’s operating capabilities. The closer the motor shaft comes to the electromagnet, the greater the pull of the shaft on the bearing, which makes the bearing unstable. Diagnostic data, however, send information to the monitoring system in real time to continually adjust the position of the motor shaft’s orbit. Such real-time data can also be used to monitor the motor’s performance.

This technology is primarily found in high horsepower, highspeed applications because of its cost. But as control schemes continue to develop and production costs decrease, active magnetic bearings will be feasible for an array of motor applications.

Moving closer to superconducting

Applying superconducting motor technology in commercial applications is the next hurdle in the innovation of motor products. This technology will revolutionize motor use around the world.

Superconductivity is a property of select materials in which virtually all resistance to the flow of electric current disappears below a certain critical temperature. These temperatures are so low (near liquid Helium at 4.2 K), that until recently, few commercial applications were feasible due to the economics of cooling the materials.

A Dutch physicist discovered low-temperature superconductivity in 1911. But it wasn’t until 1986, with the discovery of hightemperature superconducting (HTS) ceramic materials that this technology was applied to electric motors.

Motors made of HTS materials will produce higher motor magnetic fields, which will help shrink motor size and cut energy losses. Research shows energy costs of superconducting motors will be half that of present conventional highefficiency induction motors.

HTS-based motors will mostly be large (1,000 hp and above) ac synchronous motors with ceramic windings. They will drive pumps and fans in utilities, pump oil and gas, run compressors, and power other industrial commercial applications. These motors will also be powered by adjustable-speed drives — providing additional energy savings.

In March of 1996, a 200 hp HTS electric motor was demonstrated. Development is proceeding on a 1,000 hp demonstration. The goal is to have a 5,000 hp motor installed at a customer site by 2001.

While HTS technology progress is steady, there are still several obstacles to overcome before superconducting motor technology becomes commercially viable. These include reducing the overall cost, improving wire and coil performance, and establishing system reliability.

None of these obstacles require breakthrough technology - but they may require a number of years for honing and refining current accomplishments. Superconducting motors may become generally available within the next decade.

Rick Payton is director of distribution, Rockwell Automation, Cleveland.

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