In a drop-off situation, that is, when the value of the negative-sequence current
drops below the
Start value
setting, the reset timer is activated and the START
output resets after the time delay of
Reset delay time
for the DT characteristics. For
IDMT, the reset time depends on the curve type selected.
For the IDMT curves, it is possible to define minimum and maximum operate times
with the
Minimum operate time
and
Maximum operate time
settings. The
Machine
time Mult
setting parameter corresponds to the machine constant, equal to the I
2
2
t
constant of the machine, as stated by the machine manufacturer. In case there is a
mismatch between the used CT and the protected motor's nominal current values,
it is possible to fit the IDMT curves for the protected motor using the
Current
reference
setting.
The activation of the OPERATE output activates the BLK_RESTART output. The
deactivation of the OPERATE output activates the cooling timer. The timer is set
to the value entered in the
Cooling time
setting. The BLK_RESTART output is
kept active until the cooling timer is exceeded. If the negative-sequence current
increases above the set value during this period, the OPERATE output is activated
immediately.
T_ENARESTART indicates the duration for which the BLK_RESTART output remains
active, that is, it indicates the remaining time of the cooling timer. The value is
available in the monitored data view.
When the ST_EMERG_ENA emergency start is set high, the value of the
T_ENARESTART is immediately set to "False". This disables BLK_RESTART and in turn
makes the restart of the motor possible.
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operation time. The value is
available in the monitored data view.
The T_ENARESTART output indicates the duration for which the BLK_RESTART
output remains active, that is, it indicates the remaining time of the cooling timer.
The value is available in the monitored data view.
When the ST_EMERG_ENA emergency start is set high, the value of the
T_ENARESTART is immediately set to "False". This disables BLK_RESTART and in turn
makes the restart of the motor possible.
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operation time. The value is
available in the monitored data view.
4.4.5.6 Timer characteristics
MNSPTOC supports both DT and IDMT characteristics. The DT timer characteristics
can be selected with "ANSI Def. Time" or "IEC Def. Time" in the
Operating curve type
setting. The functionality is identical in both cases. When the DT characteristics
are selected, the functionality is only affected by the
Operate delay time
and
Reset
delay time
settings.
The protection relay provides two user-programmable IDMT characteristics curves,
"Inv. curve A" and "Inv. curve B".
Current-based inverse definite minimum time curve (IDMT)
In inverse-time modes, the operate time depends on the momentary value of the
current: the higher the current, the shorter the operate time. The operate time
1MRS759142 F
Protection functions
REX640
Technical Manual
843
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