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.
Figure 398: 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 some cases, the CB_CLOSED input can be active but the value of current
may not be greater than the value of the
Motor standstill A
setting. To allow
both possibilities, a time slot of 200 milliseconds is provided for current and the
CB_CLOSED input. If both events occur during this time, the motor start-up is
recognized.
The motor start-up ends either within the value of the
Str over delay time
setting from the beginning of the start-up or the opening of CB or when the
CB_CLOSED input is deactivated. The operation of the MOT_START output signal in
this operation mode is as illustrated in
Figure 399
.
This CB mode can be used in soft-started or slip ring motors for protection against
a large starting current, that is, a problem in starting and so on.
Protection functions
1MRS757644 H
760 620 series
Technical Manual
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