Motors and Drives Offer a Variety Of Technology Solutions

Variety in electric motors and their controls continue to add spice to the selection process for users of these products. Control Engineering's new research survey of 1,500 readers verifies the diversity of motor and drive products being applied in many industries. In the following results, 358 usable responses represent the survey's base (North America).

By Staff October 1, 1998
  • Torque control

  • Embedded diagnostics

  • Customized motors

  • Higher drive reliability

  • Higher motor efficiency

Variety in electric motors and their controls continue to add spice to the selection process for users of these products. Control Engineering ‘s new research survey of 1,500 readers verifies the diversity of motor and drive products being applied in many industries. In the following results, 358 usable responses represent the survey’s base (North America).

Nearly all respondents say ac motors and variable-speed drives are the most popular technology: 95% use motors; 86% use drives. DC motors and drives still “hang in there” quite well, with 67% and 56% of respondents, respectively, reporting their usage. Other technologies applied include servo, stepper, brushless dc, and linear, in decreasing order (see diagram). A surprising 20% of participants report use of integral motor/drive units. The high figure may be an anomaly because this emerging product class may not yet convey a clear name to all prospective users. (Step motors and drives will receive attention in a separate article next month.)

Despite progress toward more communication among all elements of industrial systems, CE ‘s survey indicates that most drives (nearly 71%) are stand alone. While one in five respondents use stand alone as well as networked units, only 8% say they have fully networked drives in their plants.

As for specific networks in use, the top five mentioned are: DeviceNet (34%), Interbus (18%), SERCOS (9%), and Profibus and AS-interface (both 7%). These results are based on 101 respondents with some or all networked drives. Equally significant, about 35% indicated using one of the numerous proprietary and vendor-specific communication protocols in the market.

Functions, performance

What features do customers want? Simple control/setup, convenient operator interface, pricing, and programmability are the four most desired functional features (second diagram). As for performance features, survey respondents seem less focused. Here the top desires are torque control and dynamic braking, with tripless operation and zero speed control coming in as a virtual third-place tie. However, only the first two drew over 50% response for being “very” or “somewhat” important (see performance features diagram).

Other survey results indicate that industry uses electric motors in great quantities. Percent of users and numbers vary inversely with motor size. For example, 60.3% report using motor sizes up to 1 hp, with 210 as the average number in use per respondent or location; in the 21-50 hp range, the values are 48.3% users and 41 units in use on an average site.

The future looks promising for motors and drives according to Control Engineering ‘s survey participants. Slightly more than half the respondents (51%) predict their motor purchases will remain the same and 18% say it will increase in the next 12 months. The picture for drives is similar, with 43% staying put and 21% increasing purchases. Only 5% of motor users and 4% of drives users say their purchases will decrease in the next year’s time horizon.

Supply-side views

Suppliers of motors and drives reflect generally similar developments, but their emphasis can differ.

Added reliability and efficiency are among trends in motors cited by Rockwell Automation/Reliance Electric (Cleveland, O.). Its IQ Intelligent Motor with PreAlert Technology (see CE , Nov. ’97, p. 9) embeds sensors for diagnostic data acquisition and for optical torque measurements to monitor operating conditions of the motor and connected equipment. These methods help users boost motor reliability and reduce predictive maintenance costs.

Advanced mechanical and electrical designs further lengthen motor life. “Newer, patented insulation systems, advanced electrical shielding, and magnetic bearing designs are a few of the latest changes to be found inside Reliance Electric motors,” says a company spokesman. Also in the picture are “ultra-efficient” motors with substantially higher efficiency ratings than dictated by EPAct regulations that recently went into effect.

Rockwell Automation/Allen-Bradley notes new importance for braking options on variable-speed drives (VSDs) to handle applications with overhauling loads or high inertia. (See products section for an example.) Line regeneration is an energy-saving option compared to standard methods, such as dynamic (resistor) braking, dc injection, or flux braking. “Line regeneration allows large amounts of energy contained in high-inertia [and overhauling] loads to be removed as the load is slowed, and delivered back to the ac line or to other drives instead of being wasted in the form of heat,” explains Carry Hiller, product manager for A-B Standard Drives at Mequon, Wis. “Also, lower electric bills reduce costs.”

Variable-speed duty

One development at U.S. Electrical Motors (USEM, St. Louis, Mo.) is to make motors more suitable for variable-speed usage. Perhaps the most common provision is to incorporate closed-loop feedback (encoders, tachometers, etc.) in the motor for speed control by VSDs, explains Tim Albers, USEM product manager. Current and position feedback is added to control torque with flux vector drives. He mentions another special design feature—a blower option for the entire range of ac motor sizes—intended for the more rugged conditions under variable-speed and flux vector control. USEM is also working with on-board sensors and real-time diagnostics on the motor itself.

Baldor Electric (Fort Smith, Ark.) likewise sees efficiency and quality as front-line motor developments. John A. McFarland, president of Baldor notes growing customer interest in premium-efficiency motors. These motors provide higher efficiencies than EPAct-compliant motors and were available long before that legislation became law. “The market is not drying up for premium-efficiency motors despite the effect of EPAct legislation,” comments Mr. McFarland. One indicator of quality trends is the manufacture of motors at Baldor to

“Custom motors” is another development ongoing at Baldor. “Motors can more easily be tailor-made to customer needs using computer-aided design. Special windings and special mechanical features are examples of custom motors,” says Mr. McFarland. Lead times for custom motors are also down to four weeks from twice that figure, made possible by production improvements.

Joe Howard, product specialist at GE Industrial Systems (Fort Wayne, Ind.) also mentions custom motors. He considers NEMA type ac motors in the 1-200 hp range to be more custom than stock. “This expanding product line includes special features such as tachometers and brakes, but not as an off-the-shelf offering,” he says.

Mr. Howard notes the viability of dc motors and drives shown in the survey (see above). Large installed base of dc technology is one factor of its longevity. Lower cost of the drive (not motor) is another selection factor in favor dc versus ac.

At GE Industrial Systems (GEIS, Salem, Va.), the “value equation” for ac drive technology means delivering performance to meet applications at a competitive price. Important elements needed to make this happen include reliability, efficiency, ease of use and startup, and ease of repair, according to Lincoln M. Fujita, manager of Technology Planning.

High drive reliability comes from use of GE’s Six Sigma processes for product design and manufacturing. “High efficiency demands the best power semiconductor technology, cooling architectures, and the elimination of power robbing devices such as series inductors and snubbers,” says Mr. Fujita. He also notes “New modulation techniques that allow torque control capabilities, which were unattainable until recently.”

For ease of use and startup, GEIS recommends innovative aids such as startup wizards, autotuned regulators, adaptive controls, and graphical configuration tools. For ease of repair, enhanced onboard diagnostics are valuable, but Mr. Fujita adds that a logically laid out mechanical design, captive hardware, and no hidden connections also help. Further value comes from remote services, such as GE’s OnSite Support that brings round-the-clock diagnostics support with “expert process knowledge” to customers.

Brushless servo motor family expands

Fort Smith, Ark.— BSM50 Series is the smallest, newest addition to Baldor’s servo motor family offering 1.4-162 Nm peak torque, overall. With up to 5.4 Nm peak torque from a 55-mm square × 153-mm long unit, BSM50 is said to provide “the most torque in the smallest package size available to industry.” Some models have output speed up to 12,000 rpm. Features include encapsulated, 200 °C moisture resistant multicoated wire; enclosure with shaft oil seal to meet IP65 protection; continuous 155 °C operation including thermal switch; worldwide acceptable IEC 50 standard mounting; and UL, CE, CSA approvals. Baldor Electric Co.

Line regen drive brake package

Mequon, Wis.— New 1336 Regen Line Regeneration Package is designed for high-inertia usage like centrifuges and overhauling loads of winders and conveyors. As a regenerative brake, 1336 Regen removes braking energy from an ac drive and returns it to the ac utility. It is based on A-B’s 1336 drive and works with industry standard networks (DeviceNet, ControlNet, etc.,) and A-B DriveTools software, using external modules. Ratings are 48, 78, and 180 A at 380-460 V (up to 190 hp continuous load); more braking power at 460 and 575 V is coming. The 1336 Regen also works as a regenerative common bus supply for one or more dc-input ac drives. Allen-Bradley Response Center

Enhanced ac drives have wider range

Salem, Va.— Innovation Series ac drives now span a wider size range with ratings at 600 V and medium-voltage (MV) units at 3.3, 4.16, and 6.6 kV, up to 19 MW power. MV drives use new integrated gate-commutated thyristor (IGCT) power devices for higher performance. Novel cooling, such as heat pipe technology is applied on many of the power ratings. Innovation Series can be configured for various process and drive functions. In its basic form, a tachless regulator works with a torque regulator and induction motor thermal model to obtain 0.05% or better speed regulation with detailed motor data (or 1-2% control using standard nameplate data). GE Industrial Systems

Variable-speed ac motor

Cleveland, O.— Reliance Electric G40 variable-speed ac motor delivers up to 1,250 hp at full-load efficiencies approaching 97%. G40 is both NEMA and IEC compliant to meet application needs. Control from a variable-speed inverter produces variable torque, constant torque, and constant horsepower output. The motor holds sound pressure levels at 85 dBA and meets NEMA standards for vibration levels. A ribbed-frame enclosure, cooled by a single fan, eliminates the need for cooling tubes, and the simpler design requires less air movement or force. Reliance Electric Response Center

Drive adds positioning function

Rockford, Ill.— New VLT 5000 SychPos card option adds position control (and motor synchronization) to Danfoss ac adjustable-frequency drives of the same series. The option card has a package price 50-75% under a servo system, says Danfoss. SynchPos provides 220 kHz encoder frequency, needs no extra panel space or wiring, and retains the drive’s NEMA rating. Operator interface is via the VLT drive’s local control panel. SynchPos is compatible with Profibus, DeviceNet, Modbus Plus, and LonWorks bus interfaces. It includes the control card and Basic-like programming software. Danfoss Electronic Drive

Inverter-duty motors with warranty

St. Louis, Mo.— “Invincible” is the name of the insulation system featured on USEM’s inverter-duty motors to stand up against the most severe voltage spikes. The system exceeds NEMA MG, part 31 specs; uses pulse-resistant magnet wire; and includes double dip and bake treatment to prevent breakdown of wire and insulation. A thermostat to avoid thermal overload is a standard component on these motors. The high thermal margin allows motor output of 5:1 constant torque-speed range and 10:1 variable torque range. These motors come with standard three-year and optional five-year warranty. U.S. Electrical Motors

Quick setup for servo drive

Lebanon, O.— Compact DBC III servo drive offers programming in minutes without tools via a special built-in setup panel. The operator panel also displays drive status and failure data. Diagnostics is enabled to a PC via a communications software option. DBC Series has eight models with nominal current range of 2-25 A; it can be matched with Vickers’ FAS T and N Series servo motors (also some asynchronous motor models). The single-axis digital drive features intelligent power modules that reduce unit size and integrate overload protection, built-in warning systems, and sinusoidal current waveform. Vickers Electronic Systems

Brushless dc gear motors

Chicago— Bodine Electric has extended its line of brushless dc right-angle gear motors with the 22B-3N. Brushless dc design permits peak torque of 147 lb-in. with this gear motor of smaller than usual size (8.75-in. long, 5.4 lb.). Rated torques in the 11-37 lb-in. range can be obtained with typical speeds of 500 to 42 rpm. Motors are available with 24 or 130 V windings in all ranges, and with gear ratios of 5, 10, 20, 40, and 60. Bodine Electric Co.

Small inverter, full-sized features

Chambersburg, Pa.— When big inverter features are needed in tight space requirements, call on the X2C ac inverter, says the manufacturer, TB Wood’s. X2C models through 20 hp (230 and 460 V) provide full running torque down to 3 Hz. Other features include numerous I/O connections to simplify process control; an internal regulator to smooth out winder, pump, and fan applications; local or remote operation; and advanced programming functions. The inverter has CE mark compliance with the Low Voltage Directive; with the XLF filter it also meets CE EMC directives. TB Wood’s Inc.

Modular drive family

Raleigh, N.C.— Altivar 66 sensorless flux vector drive stresses modular design and wide power range. It has 26 ratings from 1 to 350 hp for constant torque operation (to 400 hp for variable torque). With 208/230-V and 400/460-V versions, the drive is intended for global usage. A large graphical user interface with 6 x 21-character LCD screens speeds up configuration and drive operation. Numerous options include modular I/O point extensions. Square D Co.

Small drive with integral EMC filter

Alpharetta, Ga.— Siemens claims to have the “world’s smallest” sensorless vector variable-frequency drive (VFD) with integrated Class A filter. Micro Master 6SE32 measures 5.79 × 2.87 × 5.55-in. deep, weighs under 2 lb, and controls induction motors up 3 kW with built-in EMC filter. It offers space savings because several drives can be mounted side by side in a smaller cabinet and reduced installation time without external filter wiring. Torque rating of 6SE32 is up to 200% for 3 sec at nominal and low frequencies. Siemens Energy & Automation Inc.

Blower kits for low-speed apps

Grafton, Wis.— Forced ventilation kits now adapt many of Leeson’s totally enclosed, fan cooled motor models to low-speed inverter applications. A supplementary 115 V fan drive motor provides constant-velocity cooling at any motor speed. Replacement kits are easily installed in the field or in the factory. Leeson Electric Co.

Large induction motor line expands

New Berlin, Wis.— AMA Series high-efficiency ac induction motors now include NEMA 500-, 580-, and 680-frame sizes with 200-1,500 hp output, extending medium-voltage (MV) motor range down from 30,000 hp. The 3-phase, MV motors operate on wide supply voltages (2.3-6.6 kV at 50 or 60 Hz). Modular changes can alter the basic Open Design motor to Weather Protected Type II by adding a top enclosure, or to a more rugged service motor via a top-mount water-air heat exchanger. ABB Industrial Systems

150 W moving coil motors

Burlingame, Calif.— Rare-earth magnets and graphite brushes maximize torque output from RE Series 40-mm dia. × 71-mm long moving coil motors. The patented rhombic-shaped moving coil offers low electrical noise, fast acceleration, and 89% maximum efficiency. An ironless rotor allows for zero cogging and simple control. RE Series weighs 480 g (17 oz) and is rated at 150 W power and 8,200 rpm maximum speed. Maxon Precision Motors Inc.

Multiaxis servo drive

Chatsworth, Calif.— SP2k Series Digital Positioning Brushless Servodrives include power electronics to drive a servo motor and control electronics for 2 or 4 axes of motion, using a 60-MHz digital signal processor. Drive models range from 4 to 50+ Amp continuous output. SPk2 handles machine control functions with 32 isolated I/O points (24 V), expandable to 160 points. Electronic gearing is among numerous motion system functions provided. Westamp Inc.

Explosion-proof servo motors

East Aurora, N.Y.— G490 Series brushless servo motors are designed and tested for operation in CENELEC (Group IIC for Class T4) and FM Division 1 (Class I for Group A, B, C, and D) environments. Features include 115 lb-in. peak stall torque, speeds over 10,000 rpm, brakes, IEC/NEMA mounting, custom windings, and resolver-based feedback. Moog Inc. , North American Drives Operation

Small brushless dc motors

Kent, O.— A line of compact 43-mm dia. brushless dc motors offers high torque-to-inertia ratio for rapid start/stop capability. The 3-phase (8-pole, 12-slot) motors supply 22-115 W output from a choice of 12-, 24-, or 36-V inputs. Hall effect sensors provide electronic commutation. Overall package length ranges from 43 to 86 mm. Ametek Rotron Technical Motor Div.

Servo drive with DeviceNet

Amherst, N.Y.— “Intelligent” Series brushless servo drives now include DeviceNet communication to simplify control for digital positioning servos. Four drive models provide 3, 6, 10, and 20 A continuous current in the 1.1-7.6 kW power range (continuous). I/O points (6 in, 3 out) are programmable and Intelligent Series drives work with encoder- and resolver-equipped brushless motors. API Controls

Servo planetary gear motors

Hoffman Estates, Ill.— Five LP Series gearbox models (various gear ratios) and MKD digital ac servo motors combine to provide 93-3,549 lb-in. (10.5-400 Nm) max. output torque for a gamut of applications. Output speeds range from 72 to 1,600 rpm max., depending on the model. Backlash is held to Indramat Div. , Mannesmann Rexroth Corp.