4.5.6.5 Operation principle
The function can be enabled and disabled with the
Operation
setting. The
corresponding parameter values are "On" and "Off".
The operation of PSPTUV can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
OPERATE
Level
detector
BLOCK
START
t
Timer
U
1
U3P
Blocking
logic
Figure 493: Functional module diagram. U1 is used for representing positive phase
sequence voltage.
Level detector
The calculated positive-sequence voltage is compared to the set
Start value
setting.
If the value drops below the set
Start value
, the level detector enables the timer. The
Relative hysteresis
setting can be used for preventing unnecessary oscillations if the
input signal slightly varies from 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.
The level detector contains a low-level blocking functionality for cases where the
positive-sequence voltage is below the desired level. This feature is useful when
unnecessary starts and operates are wanted to avoid during, for example, an
autoreclose sequence. The low-level blocking is activated by default (
Enable block
value
is set to “Enabled”) and the blocking level can be set with the
Voltage block
value
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 undervoltage condition persists.
If the positive-sequence voltage normalizes before the module operates, the reset
timer is activated. If the reset timer reaches the value set by
Reset delay time
, the
operate 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.
Blocking logic
There are three operation modes in the blocking function. The operation modes
are controlled by the BLOCK input and the global setting in Configuration>
System> Blocking mode which selects the blocking mode. The BLOCK input can
1MRS759142 F
Protection functions
REX640
Technical Manual
881
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