GB/T 755-2025Rotating electrical machines - Rating and performance (English PDF)

Foreword

This document was issued on 1 August 2025 by the State Administration for Market Regulation and the Standardization Administration of China, and has applied since 1 February 2026.

It replaces GB/T 755-2019.

It is a GB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer, customer or inspection body applies.

1 Scope

This document is applicable to all rotating electrical machines, except rotating electrical machines for rail and road vehicles, which are covered by the IEC 60349 series of standards.

Machines within the scope of this document may also be subject to superseding, modifying or additional requirements in other standards, for example, IEC 60079 and IEC 60092.

Note: If particular clauses of this document are modified to meet special applications, for example machines subject to radioactivity or machines for aerospace, all other clauses apply insofar as they are compatible.

2 Normative references

The following normative documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.

GB/T 21210-2016 Starting performance of single-speed three-phase cage induction motors (IEC 60034-12:2016, IDT)

IEC 60027-1 Letter symbols to be used in electrical technology - Part 1: General

Note: GB/T 2987-1996 Letter symbols of parameter for electronic tubes (IEC 60027-1:1992, NEQ)

IEC 60027-4 Letter symbols to be used in electrical technology - Part 4: Rotating electric machines

IEC 60034-2 (All parts) Rotating electrical machines - Part 2: Standard methods for determining losses and efficiency from tests (excluding machines for traction vehicles)

IEC 60034-3 Rotating electrical machines - Part 3: Specific requirements for synchronous generators driven by steam turbines or combustion gas turbines

IEC 60034-5 [Rotating electrical machines - Part 5: Degrees of protection provided by the integral design of rotating electrical ma- chines (IP code) - Classification]

Note: GB/T 4942-2021 Degrees of protection provided by the integral design of rotating electrical machines (IP code) - Classification (IEC 60034-5:2020, IDT)

IEC 60034-6 Rotating electrical machines - Part 6: Methods of cooling (IC code)

Note: GB/T 1993-1993 Cooling methods for rotating electrical machines (IEC 60034-6:1991, IDT)

IEC 60034-8 Rotating electrical machines - Part 8: Terminal markings and direction of Rotation

Note: GB/T 1971-2021 Rotating electrical machines - Terminal markings and direction of rotation (IEC 60034-8:2014, IDT)

IEC 60034-12 Rotating electrical machines - Part 12: Starting performance of single-speed three-phase cage induction motors

Note: GB/T 21210-2016 Starting performance of single-speed three-phase cage induction motors (IEC 60034-12:2016, IDT)

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60050-411 and the following apply.

Note 1: For definitions concerning cooling and coolants, other than those in 3.17 to 3.22, see IEC 60034-6.

Note 2: For the purposes of this document, the term "agreement" means "agreement between the manufacturer and purchaser’.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

- IEC Electropedia: available at http://www.electropedia.org/;

- ISO online browsing platform: available at http://www.iso.org/obp

3.1 rated value: quantity value assigned, generally by a manufacturer, for a specified operating condition of a machine

Note: The rated voltage or voltage range is the rated voltage or voltage range between lines at the terminals.

[Source: GB/T 2900.25-2008, 411-51-23]

3.2 rating: set of rated values and operating conditions

[Source: GB/T 2900.25-2008, 411-51-24]

3.3 rated output: value of the output included in the rating

3.4 load: all the values of the, in case of a generator, electrical and, in case of a motor, mechanical quantities that signify the demand made on a rotating machine by an electrical circuit or a mechanism at a given instant

[Source: GB/T 2900.25-2008, 411-51-01, modified]

3.5 no-load (operation): state of a machine rotating with zero output power (but under otherwise normal operating conditions)

[Source: GB/T 2900.25-2008, 411-51-02, modified]

3.6 full load: load which causes a machine to operate at its rating

[Source: GB/T 2900.25-2008, 411-51-10]

3.7 full load value: quantity value for a machine operating at full load

[Source: GB/T 2900.25-2008, 411-51-11]

Note: This concept applies to power, torque, current, speed, etc.

3.8 rest and de-energized: complete absence of all movement and of all electrical supply or mechanical drive

[Source: GB/T 2900.25-2008, 411-51-03]

3.9 duty: statement of the load(s) to which the machine is subjected, including, if applicable, starting, electric braking, no-load and rest and de-energized periods, and including their durations and sequence in time

[Source: GB/T 2900.25-2008, 411-51-06]

3.10 duty type: continuous, short-time or periodic duty, comprising one or more loads remaining constant for the duration specified, or a non-periodic duty in which generally load and speed vary within the permissible operating range

[Source: GB/T 2900.25-2008, 411-51-13]

3.11 cyclic duration factor: ratio between the period of loading, including starting and electric braking, and the duration of the duty cycle, expressed as a percentage

[Source: GB/T 2900.25-2008, 411-51-09]

3.12 locked rotor torque: minimum measured torque the motor develops at its shaft and with the rotor locked, over all its angular positions, at rated voltage and frequency

[Source: GB/T 2900.25-2008, 411-48-06]

3.13 locked rotor current: greatest steady-state r.m.s. current taken from the line with the rotor locked, over all angular positions of its rotor, at rated voltage and frequency

[Source: GB/T 2900.25-2008, 411-48-16]

3.14 pull-up torque (of an a.c. motor): minimum steady-state asynchronous torque which the motor develops between zero speed and the speed which corresponds to the breakdown torque, when the motor is supplied at the rated voltage and frequency

Note 1: This definition does not apply to those asynchronous motors of which the torque continually decreases with increase in speed.

Note 2: In addition to the steady-state asynchronous torques, harmonic synchronous torques, which are a function of rotor load angle, will be present at specific speeds.

At such speeds, the accelerating torque may be negative for some rotor load angles.

Experience and calculation show this to be an unstable operating condition and therefore harmonic synchronous torques do not prevent motor acceleration and are excluded from this definition.

3.15 breakdown torque (of an a.c. motor): maximum steady-state asynchronous torque which the motor develops without an abrupt drop in speed, when the motor is supplied at the rated voltage and frequency

Note: This definition does not apply to asynchronous motors with torques that continually decrease with increase in speed.

3.16 pull-out torque (of a synchronous motor): maximum torque which the synchronous motor develops at synchronous speed with rated voltage, frequency and field current

3.17 cooling: procedure by means of which heat resulting from losses occurring in a machine is given up to a primary coolant, which may be continuously replaced or may itself be cooled by a secondary coolant in a heat exchanger

[Source: GB/T 2900.25-2008, 411-44-01]

3.18 coolant: medium, liquid or gas, by means of which heat is transferred

[Source: GB/T 2900.25-2008, 411-44-02]

3.19 primary coolant: medium, liquid or gas, which, being at a lower temperature than a part of a machine and in contact with it, removes heat from that part

[Source: GB/T 2900.25-2008, 411-44-03]

3.20 secondary coolant: medium, liquid or gas, which, being at a lower temperature than the primary coolant, removes the heat given up by this primary coolant by means of a heat exchanger or through the external surface of the machine

[Source: GB/T 2900.25-2008, 411-44-04]

3.21 direct cooled (inner cooled) winding: winding mainly cooled by coolant flowing in direct contact with the cooled part through hollow conductors, tubes, ducts or channels which, regardless of their orientation, form an integral part of the winding inside the main insulation

Note: In all cases when "indirect" or "direct"’ is not stated, an indirect cooled winding is implied.

[Source: GB/T 2900.25-2008, 411-44-08]

3.22 indirect cooled winding: any winding other than a direct cooled winding

Note: In all cases when "indirect" or "direct" is not stated, an indirect cooled winding is implied.

[Source: GB/T 2900.25-2008, 411-44-09]

3.23 supplementary insulation: independent insulation applied in addition to the main insulation in order to ensure protection against electric shock in the event of failure of the main insulation

3.24 moment of inertia: sum (integral) of the products of the mass elements of a body and the squares of their distances (radii) from a given axis

3.25 thermal equilibrium: state reached when the temperature rises of the heating parts of the machine do not vary by more than a gradient of 1 K per half hour

Note: Thermal equilibrium may be determined from the time-temperature rise plot when the straight lines between points at the beginning and end of two successive intervals of half hour each have a gradient of 1K or less per half hour or 2K or less per hour.

[Source: GB/T 2900.25-2008, 411-51-08, modified]