Level detector
The calculated average voltage for all three voltages is compared phase-wise to the
set
Start value
setting. If the calculated voltage value is higher than the set value of
the
Start value
setting, Level detector enables the Phase selection logic module. The
Relative hysteresis
setting can be used for preventing unnecessary oscillations if the
input signal slightly differs 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.
Phase selection logic
If the fault criteria are fulfilled in the level detector, the phase selection logic
detects the phase or phases in which the fault level is detected. If the number of
faulty phases matches with the set
Num of start phases
, the phase selection logic
activates the Timer module.
Timer
Once activated, the timer activates the START output. The operate delay time is not
settable directly but it depends on the
Operate delay Mult
setting and refresh timer
T
refresh
. The operate delay time is calculated as:
Operate delay time in s delay Mult= ⋅Operate Trefresh
(Equation 260)
When the operation timer has reached the value equal to
Operate delay time
, the
OPERATE output is activated if the overvoltage condition persists. If the average
voltage value normalizes before the module operates, the reset timer is activated.
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time. The value is
available in the monitored data view.
When the relay has tripped due to variation overvoltage protection, check
that operation is safe before closing the breaker. Clear the average
voltage value by using
PHVPTOV1 Reset mean
on the Clear menu to
prevent immediate retripping of breaker by PHVPTOV.
Considering the slow dynamic of the measurement, the protection
may remain in the START status for a long time. If the measured
voltage returns to a value lower than
Start value
, the function does not
immediately reset. The function resets when the calculated average RMS
value drops below
Start value
.
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
be controlled by a binary input, a horizontal communication input or an internal
signal of the protection relay's program. The influence of the BLOCK signal activation
is preselected with the global setting
Blocking mode
.
The
Blocking mode
setting has three blocking methods. In the “Freeze timers”
mode, the operation timer is frozen to the prevailing value, but the OPERATE output
is not deactivated when blocking is activated. In the “Block all” mode, the whole
1MRS759142 F
Protection functions
REX640
Technical Manual
917
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