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•
Differential of the third harmonic component measured both at generator neutral and
terminal side
•
Neutral side third harmonic undervoltage
27/59THN operates with the definite time DT characteristics.
The function contains a blocking functionality. Blocking deactivates all outputs and reset
timers.
4.2.7.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are “Enable” and “Disable”.
The operation of 27/59THN can be described using a module diagram. All the modules in
the diagram are explained in the next sections.
PICKUP
BLOCK
V_3H_N
TRIP
Level
detector
3
rd
harmonic
calculation
t
Timer
Differential
calculation
V_3H_A
GCB_CLOSED
INT_BLKD
V_3H_C
V_3H_B
V_3H_RES
Bias
calculation
GUID-705CF2E6-CD84-4DA4-8370-5B894BFD1789 V1 EN
Figure 205:
Functional module diagram
3rd harmonic calculation (terminal side)
3rd harmonic calculation calculates the magnitude and phase angle of the third harmonic
voltage at the generator terminal
V
3
H T
_
. Calculation of the third harmonic voltage
depends on the availability of terminal side voltage and is specified by the
Voltage
selection
setting.
•
Voltage selection
setting is set to "No voltage" if phase-to-ground voltages are not
available at the terminal side. Even in a situation where only phase-to-phase voltages
are available,
Voltage selection
is set to "No Voltage" because phase-to-phase
voltages do not contain a third harmonic component. With
Voltage selection
set to
"No Voltage", third harmonic-based ground-fault protection is based on third
harmonic neutral side undervoltage protection.
•
Voltage selection
setting is set to "Measured VG" if the terminal side voltage is fed
from an open delta voltage connection of the voltage transformer. In this case, the
terminal side third harmonic voltage
V
3
H T
_
is same as the measured open delta
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
425
Technical Manual
Содержание Relion 615 series
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