IEC 60947-8:2021 pdf download – Low-voltage switchgear and controlgear – Part 8: Control units for built-in thermal protection (PTC) for rotating electrical machines.
3 Terms and definitions, symbols and abbreviated terms 3.1 Terms and definitions For the purposes of this document, the terms and definitions given in IEC 60947-1 :2020, as well as the following terms and definitions, apply. 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 3.1.1 built-in thermal protection protection of certain parts (called protected parts) of a rotating electrical machine against excessive temperatures resulting from certain conditions of thermal overload, achieved by means of a thermal protection system, the whole or part of which is a thermally sensitive device incorporated within the machine 3.1.2 thermal protection system system intended to ensure the thermal protection of a rotating electrical machine by means of a built-in PTC thermistor together with a control unit 3.1.3 control system system to translate a particular point on the characteristic of a PTC thermistor to a switching function on the supply to the rotating electrical machine Note 1 to entry: The system is capable of being reset (either manually or automatically) when the temperature falls to the reset value. 3.1.4 protected part part of a rotating electrical machine, the temperature of which is limited to a predetermined value by the action of the thermal protection system
3.1.5 abrupt characteristic change PTC thermistor PTC thermistor for which the abrupt change in resistance for one fixed temperature is able to initiate a switching operation in the control system 3.1.6 control unit device which converts into a switching function the variation of the characteristic of a PTC thermistor Note 1 to entry: The control unit can be part of other devices or systems. 3.1.7 control circuit circuit controlling the switching device which makes and breaks the power supply 3.1.8 PTC thermistor operating temperature <TNF> thermistor temperature at which, during an increase variation of the characteristic related to the temperature is such as to cause operation of the associated control unit 3.1 .9 system operating temperature <TFS> thermistor temperature at which, during an increase of temperature, the thermistor and control unit together cause the operation of the control unit 3.1.1 0 reset temperature thermistor temperature at which, during a decrease variation of the characteristic related to the temperature is such that it permits the resetting of the control unit 3.1.1 1 positive temperature coefficient thermistor PTC thermistor thermistor, the resistance of which increases with its increasing temperature throughout the useful part of its characteristic [SOURCE: IEC 60738-1 :2006, 3.4, modified – Addition of alternative term.] 3.1.1 2 mark A thermistor PTC thermistor having the particular characteristics described in Annex A 3.1.1 3 mark A control unit control unit having the particular characteristics specified in this document and intended for operation in conjunction with a mark A thermistor 3.1.1 4 short-circuit detection control unit capable of detecting short-circuited thermistor circuits 3.1 .1 5 wire break detection control unit capable of detecting wire breaks within the PTC thermistor circuits
4 Void 5 Characteristics of control units for built-in thermal protection (PTC) 5.1 Summary of characteristics The characteristics of a control unit shall be stated in the following terms, where such terms are applicable: – type of equipment (see 5.2); – rated electrical values of the control unit (see 5.3); – rated electrical values of the characteristic of the PTC thermistors and its circuit (see 5.4); – rated electrical values of the control supply circuit (see 5.5). 5.2 Type of equipment 5.2.1 Operating temperatures of protection systems Each PTC thermistor, or PTC thermistor with control unit, shall have either a declared rated operating temperature in accordance with 5.2.2 (TNF), or a declared rated system operating temperature in accordance with 5.2.3 (TFS), or both. EXAMPLE a) Abrupt characteristic change PTC thermistor: TNF to be declared; TFS is not applicable. b) Abrupt characteristic change PTC thermistor with its control unit: TFS can be declared. For such systems the value of TFS can coincide with the value of TNF for the PTC thermistor itself. 5.2.2 Rated PTC thermistor operating temperature In the case of an abrupt characteristic change PTC thermistor, the value of the TNF shall be declared under item o) of 6.1 . It is recommended that the normal value of TNF, expressed in degrees Celsius, be selected from the series of numbers which are multiples of five.