Figure 328: Functional module diagram
Level detector
The calculated negative-sequence current is compared to the
Start value setting. If
the measured value exceeds the
Start value setting, the function activates the timer
module.
Timer
Once activated, the timer activates the
START
output. Depending on the value of
the set
Operating curve type, the time characteristics are according to DT or IDMT.
When the operation timer has reached the value set by
Operate delay time in the DT
mode or the maximum value defined by the inverse time curve, the
OPERATE
output
is activated.
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.
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.
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.
4.4.4.5
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
Protection functions
1MRS757644 H
624
620 series
Technical Manual
