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Motor terms describe different things: the motor’s output, its electrical behavior, its construction, or the larger system it operates in. The definitions below explain common engineering language and distinguish industrial motor usage from electric-vehicle terminology, where current Chinese standards define specific system terms.
How to read motor specifications and terminology
A motor term is meaningful only in context. When comparing figures or definitions, check what is measured, the units, the operating condition, and whether the item describes the motor alone or a motor-and-controller system. Industrial glossaries and vehicle standards may use overlapping language without defining every term in the same context. Nidec’s A–Z motor glossary and ABB’s motor glossary are useful indexes; a formal definition should come from the standard applicable to the equipment and jurisdiction.
Quantities and performance
Torque
Torque is the turning effect a motor produces at its shaft. It is commonly expressed in newton-metres (N·m). A torque value should be read alongside speed and the conditions under which it is available; a single number does not describe performance across the motor’s entire operating range.
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Speed
Motor speed is the rate of shaft rotation, commonly given in revolutions per minute (r/min or rpm). The specified speed may be a rated operating point, a limit, or a value measured under a particular load, so the accompanying specification matters.
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Power
Mechanical output power describes the rate at which the motor delivers work at its shaft. It is commonly stated in watts or kilowatts. Because output power depends on both torque and rotational speed, compare power figures only when the operating point and whether the figure is continuous or short-term are clear.
Efficiency and losses
Efficiency is the ratio of useful output power to input power, expressed as a percentage. Losses are the part of the input energy that does not become useful output under the stated conditions; they contribute to heating and may include electrical, magnetic, mechanical, and other losses. A motor efficiency figure is not automatically the efficiency of a complete drive, which may also include a controller and other equipment.
Torque ripple
Torque ripple is variation in torque around a motor’s average torque during operation. It can affect smoothness, vibration, noise, and the performance of the driven equipment. The amount depends on motor design and operating conditions; a reported value is useful only with its measurement method and conditions.
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Temperature rise
Temperature rise is the increase in a motor’s temperature above a stated reference, often the surrounding ambient temperature. It is not the same as the motor’s absolute temperature. Interpret it with the measurement location, ambient conditions, load, and duration of operation.
Thermal resistance
Thermal resistance describes how strongly a path or component resists heat flow. It links a temperature difference to heat transfer and is typically expressed in kelvins per watt (K/W). The specified heat path and test or calculation conditions determine what the value represents.
Electrical and electromagnetic terms
Eddy current and eddy-current loss
Eddy currents are circulating currents induced within conductive material by a changing magnetic field. They cause eddy-current loss, which appears as heat. Motor design can limit these currents, for example by using laminated magnetic cores, but the resulting loss depends on the material, magnetic conditions, and operating frequency.
Equivalent circuit
An equivalent circuit is a simplified electrical model used to represent a motor’s behavior. Its components stand in for electrical and magnetic effects, helping engineers analyze current, voltage, power, and performance. It is a model for a stated purpose, not a literal map of every physical part of the motor.
Three-phase connection with an inverter
A three-phase inverter supplies controlled electrical power to a motor through three phase connections. The inverter’s output and the motor’s winding connection must be understood together: a connection diagram identifies how the windings are arranged, while the inverter controls the electrical supply. Do not infer a motor’s permissible voltage, current, or connection from the phrase alone; use its nameplate and applicable documentation.
Tachogenerator
A tachogenerator is a device that produces an electrical signal related to rotational speed. It can be used for speed measurement or feedback in a control system. Its output and accuracy depend on the specific device and installation.
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Motor types and construction language
Induction (asynchronous) motor
An induction motor produces rotor current through electromagnetic induction rather than requiring a direct electrical connection to the rotor winding for that purpose. “Asynchronous” refers to the fact that, in normal motoring operation, the rotor does not turn at exactly the rotating magnetic field’s synchronous speed. The term is common in industrial applications; check the motor’s design and operating mode when interpreting performance specifications.
DC motor
A DC motor is designed to operate from direct-current electrical power. The broad label covers different constructions and control methods, so it does not by itself establish whether a motor uses brushes, its speed-control behavior, or its intended application.
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Motor glossaries also cover enclosure and application language, including terminology for hazardous locations. These terms concern how a motor is built or where it may be used; they are not interchangeable with performance ratings. Confirm the exact protection, certification, and installation requirements for the location and equipment. ABB’s glossary includes common motor types and application terms.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Electric-vehicle drive terms and standards
Drive motor
In GB/T 18488-2024, a Chinese national standard for electric-vehicle drive motors and controllers, a drive motor is defined as: “An electrical device that converts electrical energy into mechanical energy to provide driving force for the vehicle. This device also has the function of converting mechanical energy into electrical energy.” The reverse conversion allows the drive motor to act as a generator in appropriate operating modes. This is a formal definition in that standard, not a universal definition for every industrial motor.
Drive-motor controller
GB/T 18488-2024 defines a drive-motor controller as “A device that controls the transmission of energy between a power source and a drive motor.” In practical terms, it manages electrical energy flow and motor operation; it is distinct from the motor itself.
Drive-motor system
The drive-motor system is the motor, its controller, and the auxiliary devices needed for operation. This system-level term matters when reading requirements or test results: a value stated for a system should not be treated as a motor-only specification unless the document says so.
Vehicle, trailer, and combination-vehicle terminology
For vehicle-type terms such as vehicle, trailer, and combination vehicle, consult GB/T 3730.1-2022 rather than assuming industrial motor definitions apply. China’s State Administration for Market Regulation and Standardization Administration issued this standard on 2022-12-30; it took effect on 2023-07-01 and replaced the 2001 edition. Its scope is vehicle terminology, not the technical performance of a motor.
Quick Recap
Which standard to consult
| Question | Relevant source | Scope |
|---|---|---|
| What vehicle category or combination-vehicle term applies? | GB/T 3730.1-2022 | Vehicle, trailer, and combination-vehicle terminology; issued 2022-12-30 and effective 2023-07-01. |
| What do drive motor, controller, and drive-motor system mean, or what requirements and tests apply? | GB/T 18488-2024 | Drive motors and controllers, including terminology, model naming, technical requirements, tests, inspections, and marking; issued and applied 2024-05-28. |
| What does an industrial motor glossary term mean in common usage? | Nidec glossary or ABB glossary | General motor terminology and types; use the applicable engineering standard for formal requirements. |
A practical way to compare motor terms or ratings
- Identify the application. Establish whether the document concerns industrial machinery, vehicle propulsion, or another use.
- Identify the system level. Determine whether the term or figure applies to the motor, controller, or integrated drive system.
- Read the operating point. Note units, speed, load, temperature, supply, and any stated duration or duty conditions.
- Use the right authority. Use an industry glossary to decode common language, then use the relevant standard and equipment documentation for formal definitions and limits.
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