Figure 3.15-3 Timer element
The time characteristic is according to DT. When the operation timer has reached the value set by
27_Op_T and 27_Alm_Ena=0, the 27_Op output is activated if the under voltage condition
persists; The time characteristic is according to DT. When the operation timer has reached the
value set by 27_Op_T and 27_Alm_Ena=1, the 27_Alm output is activated If the three phase
voltages normalize before the module operates, the operation resets with a time delay of 30ms.
Note: when the 27 relay is used as capacitor under voltage protection, the CB open position will
block 27 relay by connecting the CB open position to the 27_BLK input.
3.15.3 27 Application Scope
27 relay is applied to power system elements, such as generators, transformers, motors and
power lines, to detect low voltage conditions. Low voltage conditions are caused by abnormal
operation or a fault in the power system. Another application is the detection of a no-voltage
condition, for example before the energization of a high voltage line, or an automatic breaker trip in
case of a blackout.
3.15.4 27 Settings
In the following table, i is the protection stage number, it can be set according to the requirements.
Table 3.15-3 27 load shedding settings
To Next Page