3.16.2 27P Protection Principle
The positive-sequence under voltage protection function can be enabled or disabled by setting the
corresponding 27P_Ena parameter values as "1" or "0".
The operation of the positive-sequence under voltage protection can be described using a module
diagram. All the modules in the diagram are explained in the next sections.
The functional module diagram is shown as below:
Figure 3.16-2 Functional module diagram
The calculated positive-sequence voltage is compared to the set 27P_Vol_Str setting. If the value
drops below the set 27P_Vol_Str and no block signal is activated, the timer and 227P_Str signal
are activated.
A low-level blocking functionality for cases where the positive-sequence voltage is below the
desired level is applied. This feature is useful when unnecessary starts and operates are wanted
to avoid during, for example, an auto reclose sequence. The low-level blocking is activated by
default (27P_Vol_Blk_Ena is set to ā1ā) and the blocking level can be set with the 27P_Vol_Blk
setting.
Where:
27P_Vol_Str is the preset value to check for the voltage violation.
27P_Vol_Blk_Ena can enable internal blocking.
27P_Vol_Blk is the internal blocking voltage level.
27P_Op_T is operating delay time for 59P.
The time characteristic is according to DT. When the operation timer has reached the value set by
27P_Op_T, the 27P_Op output is activated if the under voltage condition persists. If the
positive-sequence voltage normalizes before the module operates, the operation resets with a
time delay of 30ms.
The binary input 27P_Blk can be used to block the function. The activation of the 27P_Blk input
deactivates all outputs and resets internal timers. The binary input 27P_Blk_Str can be used to
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