GE G60 UR Series, Instruction Manual

Page: 257 / 634

GE Multilin G60 Generator Protection System 5-125
5 SETTINGS 5.6 GROUPED ELEMENTS
5
5.6.3 DISTANCE
a) MAIN MENU
PATH: SETTINGS
ÖØ
GROUPED ELEMENTS
Ö
SETTING GROUP 1(6)
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DISTANCE
Four common settings are available for distance protection. The
DISTANCE SOURCE
identifies the signal source for all dis-
tance functions. The mho distance functions use a dynamic characteristic: the positive-sequence voltage – either memo-
rized or actual – is used as a polarizing signal. The memory voltage is also used by the built-in directional supervising
functions applied for both the mho and quad characteristics.
The
MEMORY DURATION
setting specifies the length of time a memorized positive-sequence voltage should be used in the
distance calculations. After this interval expires, the relay checks the magnitude of the actual positive-sequence voltage. If
it is higher than 10% of the nominal, the actual voltage is used, if lower – the memory voltage continues to be used.
The memory is established when the positive-sequence voltage stays above 80% of its nominal value for five power system
cycles. For this reason it is important to ensure that the nominal secondary voltage of the VT is entered correctly under the
SETTINGS
ÖØ
SYSTEM SETUP
Ö
AC INPUTS
ÖØ
VOLTAGE BANK
menu.
Set
MEMORY DURATION
long enough to ensure stability on close-in reverse three-phase faults. For this purpose, the maxi-
mum fault clearing time (breaker fail time) in the substation should be considered. On the other hand, the
MEMORY DURA-
TION
cannot be too long as the power system may experience power swing conditions rotating the voltage and current
phasors slowly while the memory voltage is static, as frozen at the beginning of the fault. Keeping the memory in effect for
too long may eventually lead to incorrect operation of the distance functions.
The distance zones can be forced to become self-polarized through the
FORCE SELF-POLAR
setting. Any user-selected con-
dition (FlexLogic™ operand) can be configured to force self-polarization. When the selected operand is asserted (logic 1),
the distance functions become self-polarized regardless of other memory voltage logic conditions. When the selected oper-
and is de-asserted (logic 0), the distance functions follow other conditions of the memory voltage logic as shown below.
The distance zones can be forced to become memory-polarized through the
FORCE MEM-POLAR
setting. Any user-selected
condition (any FlexLogic™ operand) can be configured to force memory polarization. When the selected operand is
asserted (logic 1), the distance functions become memory-polarized regardless of the positive-sequence voltage magni-
tude at this time. When the selected operand is de-asserted (logic 0), the distance functions follow other conditions of the
memory voltage logic.
The
FORCE SELF-POLAR
and
FORCE MEM-POLAR
settings should never be asserted simultaneously. If this happens, the logic
will give higher priority to forcing self-polarization as indicated in the logic below. This is consistent with the overall philoso-
phy of distance memory polarization.
The memory polarization cannot be applied permanently but for a limited time only; the self-polarization may be
applied permanently and therefore should take higher priority.
„
DISTANCE
„
DISTANCE
SOURCE: SRC 1
Range: SRC 1, SRC 2, SRC 3, SRC 4
MESSAGE
MEMORY
DURATION: 10 cycles
Range: 5 to 25 cycles in steps of 1
MESSAGE
FORCE SELF-POLAR:
Off
Range: FlexLogic™ operand
MESSAGE
FORCE MEM-POLAR:
Off
Range: FlexLogic™ operand
MESSAGE
„
PHASE DISTANCE Z1
„
See page 5–126.
MESSAGE
„
PHASE DISTANCE Z2
„
See page 5–126.
MESSAGE
„
PHASE DISTANCE Z3
„
See page 5–126.
NOTE