IEC 60947-4-2:2020 pdf free download – Low-voltage switchgear and controlgear
5.3.5.4.1
Starting characteristics of squirrel cage and hermetic refrigerationmotors
a) One direction of rotation with the inclusion of phase-control capability to provide any combination of controlled acceleration to normal speed,controlled deceleration tostandstill， or an occasional manoeuvre without de-energizing the controller (AC-3a，AC-8a).
b) One direction of rotation with the inclusion of phase-control capability to provide controlled acceleration to normal speed.Controllers and starters are rated for starting and stoppingduty cycles only (AC-3b，AC-8b); for example, after starting, the motor may be connectedinto a circuit that bypasses the semiconductor motor controller or starter.
Two directions of rotation may be accomplished by reversing the connections to the controlleror motor by means that are beyond the scope of this document,but are covered by therelevant product standard for the selected means.
Two directions of rotation may also be accomplished by phase reversing within the controlleror starter. The requirements for this operation will vary with each application.Therefore, thisis subject to agreement between manufacturer and user.
Due to the control capability of controllers and starters， the current during starting, stopping,and any operation will differ from the conventional values of the prospective locked rotorcurrent listed in Table 9.
5.3.5.4.2 Starting characteristics of rheostatic rotor starters with controllersenergizing the stator (AC-2a, AC-2b)
Starters can be used to provide reduced voltage excitation to the stator windings of a slip ringmotor，and thereby reduce the number of switching steps required in the rotor circuit. Formost applications, one or two starting steps are adequate depending upon load torque andinertia, and the severity of start required.
5.7.4Designation and current settings of overload relays
Overload relays are designated by their current setting (or the upper and lower limits of thecurrent setting range, if adjustable) and their trip class.
The current setting (or current setting range) shall be marked on the relays.
However,if the current setting is influenced by the conditions of use or other factors whichcannot readily be marked on the relay, then the relay or any interchangeable parts thereof (forexample heaters，operating coils or current transformers) shall carry a number or anidentifying mark which makes it possible to obtain the relevant information from themanufacturer or his catalogue or, preferably, from data furnished with the starter.
ln the case of current transformer operated overload relays，the marking may refer either tothe primary current of the current transformer through which they are supplied or to thecurrent setting of the overload relays. In either case, the ratio of the current transformer shallbe stated.
5.7.5Time-current characteristics of overload relays
Typical time-current characteristics shall be given in the form of curves supplied by themanufacturer. These curves shall indicate how the tripping time,starting from the cold state(see 5.7.6),varies with the current up to a value of at least maximum (X ×le) value. Themanufacturer shall be prepared to indicate，by suitable means，the general tolerancesapplicable to these curves and the conductor cross-sections used for establishing thesecurves (see 9.3.3.6.5, item c)).
lt is recommended that the current be plotted as abscissae and the time as ordinates, usinglogarithmic scales. It is recommended that the current be plotted as multiples of the settingcurrent and the time in seconds on the standard graph sheet detailed in IEC 60269-1.