GB 755-1987 General requirements for rotating electrical machines
1 Scope
This standard is applicable to all types of rotating electrical machines (hereinafter referred to as machines), except electrical machines for control and traction use.
Where there are additional requirements not specified in this standard for each type of electrical machines, supplementary provisions shall be made in the standard for this type of electrical machines.
If some types of electrical machines have special requirements in some provisions of this standard, special requirements shall be made in the product standards of this type of electrical machines.
2 Terms and definitions
For the definitions of general terms used in this standard, reference shall be made to GB 2900.25 Electrotechnical terminology - Electrical machines.
For the purpose of this standard, the following definitions apply:
2.1
rating
whole of the numerical values of the electrical and mechanical quantities with their durations and sequence assigned to the machine by the manufacturer and stated on the rating plate, the machine complying with the specified conditions
2.2
rated value
numerical value of a quantity included in the rating
2.3
rated output
numerical value of the output included in the rating
2.4
load
all the numerical values of the electrical and mechanical quantities that signify the demand to be made on a rotating machine by an electrical circuit or a mechanism at a given instant
2.5
no-load (operation)
state of a machine rotating with zero output power (but under otherwise normal operating conditions)
2.6
full load
highest value of load specified for a machine operating at rated output
2.7
full load power
highest value of power specified for a machine operating at rated output
Note: This concept also applies to torque, current, speed, etc.
2.8
rest and de-energized
complete absence of all movement and of all electrical supply or mechanical drive
2.9
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
2.10
duty type
a 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
2.11
thermal equilibrium
state reached when the temperature rises of the several parts of the machine do not vary by more than 2K over a period of 1h
2.12
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
2.13
locked rotor torque
minimum measured torque which the motor develops with the rotor locked and rated voltage applied at rated frequency
2.14
locked rotor current
measured steady-state root-mean-square current taken from the line with the rotor locked with rated voltage and frequency applied
2.15
pull-up torque (of an a.c. motor)
minimum 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
This definition does not apply to those asynchronous motors of which the torque continually decreases with increase in speed.
Note: This value applies to the usual mean torque characteristic which excludes transient effects.
2.16
breakdown torque (of an a.c. motor)
maximum torque which the motor develops with rated voltage and frequency applied at operating temperature without an abrupt drop in speed
This definition does not apply to those asynchronous motors of which the torque continually decreases with increase in speed.
Note: This value applies to the usual mean torque characteristic which excludes transient effects.
2.17
pull-out torque (of a synchronous motor)
maximum torque which the synchronous motor develops at operating temperature and at synchronous speed with rated voltage, frequency and field current
2.18
cooling
procedure by means of which heat resulting from losses occurring in a machine is given up first to a primary coolant, by increasing its temperature. The heated primary coolant may be replaced by a new coolant at a lower temperature or may be cooled by a secondary coolant in some form of heat exchanger
3 Duty and rating
3.1 Rules for declaration of duty and for selection of a class of rating
3.1.1 Duty
The duty may be described by one of the duty types defined in 3.2, or by the specification of another duty by the purchaser.
3.1.2 Declaration of duty
It is the responsibility of the purchaser to declare the duty as accurately as possible. In certain cases, where the load does not vary or where it varies in a known manner, the duty may be declared numerically or with the aid of a time sequence graph of the variable quantities.
If the time sequence is indeterminate, a fictitious time sequence (duty types S2 to S8) not less onerous than the true one, shall be selected, or the duty type S9 shall be applied. If the duty is not stated, duty type S1 (continuous running duty) applies.
3.1.3 Rating
The rating shall be selected by the manufacturer according to the classes specified in 3.3. The class of rating selected shall normally be maximum continuous rating based on duty type S1 or short-time rating based on duty type S2. If this is not possible, a periodic duty type rating based on one of the duty types S3 to S8 (periodic duty) or the non-periodic duty type rating based on the duty type S9 (non-periodic duty) shall be selected.
3.1.4 Selection of a class of rating
1 Scope
2 Terms and definitions
3 Duty and rating
4 Operating conditions
5 Temperature rise
6 Dielectric tests
7 Other characteristics
8 Commutation
9 Tolerances
10 Rating plate and markings
11 Waveform distortion
12 Correspondence between voltage and output
13 Constructional requirements
14 Efficiency and loss
15 Test items
