GE L90 Instruction Manual page 133

5 SETTINGS
See Chapter 9 for samples to create a reliable
• BLOCK GPS TIME REF: This setting signals to the L90 that the time reference is not valid. The time reference may be
not accurate due to problems with the GPS receiver. The user must to be aware of the case when a GPS satellite
receiver loses its satellite signal and reverts to its own calibrated crystal oscillator. In this case, accuracy degrades in
time and may eventually cause relay misoperation. Verification from the manufacturer of receiver accuracy not worse
than 250 µs and the presence of an alarm contact indicating loss of the satellite signal is strongly recommended. If the
time reference accuracy cannot be guaranteed, it should be relayed to the L90 via contact inputs and GPS compensa-
tion effectively blocked using the contact position in conjunction with the
typically a signal from the GPS receiver signaling problems or time inaccuracy.
• MAX CHNL ASYMMETRY: This setting detects excessive channel asymmetry. The same threshold is applied to both
the channels, while the following per-channel FlexLogic™ operands are generated: 87L DIFF 1 MAX ASYM and 87L
DIFF 2 MAX ASYM. These operands can be used to alarm on problems with communication equipment and/or to
decide whether channel asymmetry compensation remains in operation should the GPS-based time reference be lost.
Channel asymmetry is measured if both terminals of a given channel have valid time reference.
• ROUND TRIP TIME CHANGE: This setting detects changes in round trip time. This threshold is applied to both chan-
nels, while the 87L DIFF 1 TIME CHNG and 87L DIFF 2 TIME CHNG ASYM per-channel FlexLogic™ operands are
generated. These operands can be used to alarm on problems with communication equipment and/or to decide
whether channel asymmetry compensation remains in operation should the GPS-based time reference be lost.
IRIG-B FAILURE
DETECTED
SETTINGS
BLOCK GPS TIME REF:
Off = 0
IRIG-B SIGNAL TYPE:
None = 0
CHNL ASYM COMP:
Off = 0
DATA FROM REMOTE
TERMINAL 1
87L Ch 1 Status (OK=1)
87L GPS 1 Status (OK=1)
DATA FROM REMOTE
TERMINAL 2
87L Ch 2 Status (OK=1)
87L GPS 2 Status (OK=1)
Figure 5–10: CHANNEL ASYMMETRY COMPENSATION LOGIC
GE Multilin
CHNL ASYM COMP
FLEXLOGIC OPERAND
5 sec
87L DIFF PFLL FAIL
SETTINGS
MAX CHNL ASYMMETRY:
ROUND TRIP TIME
FLEXLOGIC OPERAND
CHANGE:
87L DIFF GPS 1 FAIL
RUN
Ch1 Asymmetry > MAX
ACTUAL VALUE
Ch1 Asymmetry
RUN
ACTUAL VALUE
Ch1 T-Time New -
Ch1 Round Trip Time
Ch1 T-Time Old >
CHANGE
FLEXLOGIC OPERAND
87L DIFF GPS 2 FAIL
RUN
Ch2 Asymmetry > MAX
ACTUAL VALUE
Ch2 Asymmetry
RUN
ACTUAL VALUE
Ch2 T-Time New -
Ch2 Round Trip Time
Ch2 T-Time Old >
CHANGE
L90 Line Differential Relay
setting.
BLOCK GPS TIME REF
0
5.3 SYSTEM SETUP
setting. This setting is
To Remote Relays
Channel 1 and 2
87L GPS Status Fail
5
FLEXLOGIC OPERAND
87L DIFF GPS FAIL
GPS COMPENSATION
RUN
Use Calculated GPS
Correction
Update GPS Correction
Memory
Use Memorized GPS
Correction
Use GPS Correction
of Zero
FLEXLOGIC OPERAND
87L DIFF 1 MAX ASYM
FLEXLOGIC OPERAND
87L DIFF 1 TIME CHNG
FLEXLOGIC OPERAND
87L DIFF 2 MAX ASYM
FLEXLOGIC OPERAND
87L DIFF 2 TIME CHNG
831025A4.CDR
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