ABB Relion 620 Series - Page 770

AI_VALUE OPERATE
Level
detector
Blocking
logic
BLOCK
START
Timer
ENA_ADD
t
Figure 404: Functional module diagram
Level detector
The level detector compares AI_VALUE to the Start value setting. The Operation
mode setting defines the direction of the level detector.
Table 730: Operation mode types
Operation Mode Description
"Under"
If the input signal AI_VALUE is lower than
the set value of the "Start value" setting, the
level detector enables the timer module.
"Over"
If the input signal AI_VALUE exceeds the
set value of the Start value setting, the level
detector enables the timer module.
The Absolute hysteresis setting can be used for preventing unnecessary oscillations
if the input signal is slightly above or below the Start value setting. After leaving the
hysteresis area, the start condition has to be fulfilled again and it is not sufficient
for the signal to only return to the hysteresis area. If the ENA_ADD input is activated,
the threshold value of the internal comparator is the sum of the
Start value Add
and Start value settings. The resulting threshold value for the comparator can be
increased or decreased depending on the sign and value of the Start value Add
setting.
Timer
Once activated, the timer activates the START output. The time characteristic is
according to DT. When the operation timer has reached the value set by Operate
delay time , the OPERATE output is activated. If the starting condition disappears
before the module operates, the reset timer is activated. If the reset timer reaches
the value set by Reset delay time , the operation timer resets and the START output
is deactivated.
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.
Protection functions
1MRS757644 H
770 620 series
Technical Manual