Table 603: Special conditions
Condition Description
U3P connected to real measurements The function can work with at least one volt-
age channel connected.
URES calculated The function requires that all three voltage
channels from the terminal side are connec-
ted to calculate residual voltage. Setting
VT
connection
must be "Wye" in that particular
UTVTR.
UNEUT calculated The function requires that all three voltage
channels from the neutral side are connec-
ted to calculate residual voltage. Setting
VT
connection
must be "Wye" in that particular
UTVTR.
Improper analog channel configuration causes a validation error if the analog
channels are not completely configured or they do not match with certain settings.
For troubleshooting, check the contents of this chapter and also the preprocessing
blocks in this document. The configuration can be written to the protection relay
once the mismatch is corrected.
4.2.8.5 Operation principle
The function can be enabled and disabled with the
Operation
setting. The
corresponding parameter values are “On” and “Off”.
The operation of the third harmonic-based stator earth-fault protection function
can be described using a module diagram. All the modules in the diagram are
explained in the next sections.
START
BLOCK
UNEUT
U_3H_N
OPERATE
Level
detector
3
rd
harmonic
calculation
Timer
Differential
calculation
U3P
U_3H_B
U_3H_C
GCB_CLOSED
INT_BLKD
U_3H_RES
Bias
calculation
URES
t
Figure 313: 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 Ū
3H_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-earth 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
1MRS759142 F
Protection functions
REX640
Technical Manual
543
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