ABB RELION 620 Series Technical Manual page 764

Section 4
Protection functions
758
In the "IIt & stall" mode, the function calculates the thermal stress of the motor during
the start-up condition. The start-up condition is detected by monitoring the TRMS
currents.
In the "IIt & stall, CB" mode, the function calculates the thermal stress of the motor
during the start-up condition but the start-up condition is detected by monitoring the
TRMS current as well as the circuit breaker status.
In both the "IIt & stall" and "IIt & stall, CB" mode, the function also checks for motor
stalling by monitoring the speed switch.
When the measured current value is used for start-up supervision in the "IIt" and "IIt
& stall" modes, the module initially recognizes the de-energized condition of the
motor when the values of all three phase currents are less than Motor standstill A for
longer than 100 milliseconds. If any of the phase currents of the de-energized
condition rises to a value equal to or greater than Motor standstill A, the MOT_START
output signal is activated indicating that the motor start-up is in progress. The
MOT_START output remains active until the values of all three phase currents drop
below 90 percent of the set value of Start detection A and remain below that level for
a time of Str over delay time, that is, until the start-up situation is over.
GUID-4475BDFB-57AE-4BFD-9EE7-AE7672F7206E V2 EN
Figure 388: Functionality of start-up supervision in the "IIt and IIt&stall" mode
In case of the "IIt, CB" or "IIt & stall, CB" modes, the function initially recognizes the
de-energized condition of the motor when the value of all three phase currents is below
the value of the Motor standstill A setting for 100 milliseconds. The beginning of the
motor start-up is recognized when CB is closed, that is, when the CB_CLOSED input
is activated and at least one phase current value exceeds the Motor standstill A setting.
These two events do not take place at the same instant, that is, the CB main contact is
closed first, in which case the phase current value rises above 0.1 pu and after some
delay the CB auxiliary contact gives the information of the CB_CLOSED input. In
1MRS757644 F
620 series
Technical Manual