ABB RELION REX640 Technical Manual page 1008

Section 4
Protection functions
1002
Repeated starts increase the temperature to a high value in the stator or rotor windings,
or both, unless enough time is allowed for the heat to dissipate. To ensure a safe
operation it is necessary to provide a fixed-time interval between starts or limit the
number of starts within a period of time. This is why the motor manufacturers have
restrictions on how many starts are allowed in a defined time interval. This function
does not allow starting of the motor if the number of starts exceeds the set level in the
register that calculates them. This insures that the thermal effects on the motor for
consecutive starts stay within permissible levels.
For example, the motor manufacturer may state that three starts at the maximum are
allowed within 4 hours and the start-up situation time is 60 seconds. By initiating three
successive starts we reach the situation as illustrated. As a result, the value of the
register adds up to a total of 180 seconds. Right after the third start has been initiated,
the output lock of start of motor is activated and the fourth start will not be allowed,
provided the time limit has been set to 121 seconds.
Furthermore, a maximum of three starts in 4 hours means that the value of the register
should reach the set start time counter limit within 4 hours to allow a new start.
Accordingly, the start time counter reduction should be 60 seconds in 4 hours and
should thus be set to 60 s / 4 h = 15 s / h.
GUID-3D945445-366F-4F08-B012-8B1B81DB4589 V1 EN
Figure 543: Typical motor-starting and capability curves
t ( n ) 1 t margin
∑ = − ⋅ +
si
GUID-59BCE280-BFA6-4C39-A468-14E7793E4E17 V1 EN
Cumulative time Lim
Setting of
Cumulative time Lim is calculated by
1MRS759142 C
(Equation 238)
REX640
Technical Manual