ABB RELION REX640, Техническое руководство, Страница: 1097 / 1960

Figure 616: Functionality of start-up supervision in the "IIt, CB" mode and the "IIt
and stall, CB" mode
The Str over delay time setting has different purposes in different modes of
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 R i t dt
s s
t
=
( )
∫ 2
0
(Equation 282)
1MRS759142 F Protection functions
REX640
Technical Manual
1097