BLOCK
U_LOW
Level
detector
V_A_AB
V_B_BC
V_C_CA
t
Timer
GUID-CD8F77F1-6350-4C18-BA29-D8D68A5F1163 V1 EN
Figure 337:
Functional module diagram
Level detector
The fundamental frequency component of the measured three-phase voltages over the
range of 10...70 Hz is compared phase-wise to the set
Pickup value
. If the measured value
is lower than the set value of the
Pickup value
setting, the Level detector enables the phase
selection logic module. The
Relative hysteresis
setting can be used for preventing
unnecessary oscillations if the input signal slightly varies above or below the
Pickup value
setting. After leaving the hysteresis area, the pickup condition has to be fulfilled again and
it is not sufficient for the signal to only return back to the hysteresis area.
The
Voltage selection
setting is used for selecting the phase-to-ground or phase-to-phase
voltages for protection.
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 match
with the set
Num of pickup phases
, the phase selection logic activates the Timer.
Timer
Once activated, the Timer activates the
PICKUP
output. The time characteristic is definite
time only.
When the operation timer has reached the value set by
Trip delay time
, the
TRIP
output
is activated.
In a drop-off situation, that is, when a fault suddenly disappears before the trip delay is
exceeded, the reset state is activated. The reset timer runs until the set
Reset delay time
value is exceeded. If the drop-off situation exceeds the set
Reset delay time
, the Timer is
reset and the
PICKUP
output is deactivated.
Blocking logic
There are three operation modes in the blocking functionality. The operation modes are
controlled by the
BLOCK
input and the global setting
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
Section 4
1MAC059074-MB A
Protection functions
674
615 series ANSI
Technical Manual
Summary of Contents for Relion 615 series
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