ABB RELION REX640 Technical Manual page 1097

1MRS759142 F
Figure 616: Functionality of start-up supervision in the "IIt, CB" mode and the "IIt
and stall, CB" mode
The
operation.
• In the "IIt" or "IIt & stall" modes, the aim of this setting is to check for the
completion of the motor start-up period. The purpose of this time delay setting
is to allow for short interruptions in the current without changing the state of
the MOT_START output. In this mode of operation, the value of the setting is in
the range of around 100 milliseconds.
• In the "IIt, CB" or "IIt & stall, CB" modes, the purpose of this setting is to check for
the life of the protection scheme after the CB_CLOSED input has been activated.
Based on the values of the phase currents, the completion of the start-up period
cannot be judged. So in this mode of operation, the value of the time delay
setting can even be as high as within the range of seconds, for example around
30 seconds.
The activation of the BLOCK input signal deactivates the MOT_START output.
Thermal stress calculator
Because of the high current surges during the start-up period, a thermal stress is
imposed on the rotor. With less air circulation in the ventilation of the rotor before
it reaches its full speed, the situation becomes even worse. Consequently, a long
start-up causes a rapid heating of the rotor.
This module calculates the thermal stress developed in the motor during start-up.
The heat developed during the starting can be calculated with the equation.
=
W
REX640
Technical Manual
Str over delay time setting has different purposes in different modes of
t
( )
∫
2
R i t dt
s s
0
Protection functions
(Equation 282)
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