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LPS-O Line Protection System GE Power Management
1.9 OUT-OF-STEP TRIPPING 1 PRODUCT DESCRIPTION
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1.9.3 OUT-OF-STEP DETECTION
The actual out-of-step detection in the OST option is accomplished by a software algorithm. This algorithm is
represented by the logic diagram in Figure 1–10: OUT-OF-STEP TRIPPING LOGIC DIAGRAM on page 1–23.
The operation of this logic diagram is explained below. Note: this discussion assumes that Protection Setting
1402:
NUMBRCHAR
= 3 and all three OST Mho characteristics are used.
STEP 1:
The power swing enters the OUTER characteristic. Thus AND61 will have one input from the OUTER and a
second input from OR61 since NOT61 has no input. If the swing impedance remains between the OUTER and
MIDDLE characteristics for the pickup setting of TLOS1, TLOS1 operates, sealing in one input of AND61.
When a fault occurs, the OUTER and MIDDLE characteristics operate almost simultaneously, and the MIDDLE
blocks AND61 through NOT61, thus preventing TLOS1 from operating.
STEP 2:
The swing now enters the MIDDLE characteristic but remains outside the INNER characteristic. One input of
AND62 is energized by TLOS1, a second input is proved by the MIDDLE, and the third is supplied by NOT62.
If the swing impedance remains between the MIDDLE and INNER characteristics long enough for TLOS2 to
pick up, TLOS2 seals in the lower two inputs to AND62. AND62 is therefore controlled by TLOS1, which in turn
is controlled by the OUTER characteristic.
STEP 3:
The swing now enters the INNER characteristic. One input to AND63 is provided by TLOS2, the second by the
INNER. If the swing impedance remains inside the INNER characteristic for the pickup setting of TLOS3,
TLOS3 will provide one input to AND64. At this point the decision to trip has been made and sealed in. The
out-of-step tripping output will be provided immediately if Protection Setting 1403:
TRIPIN_OUT
= IN.
STEP 4:
The swing now leaves the INNER characteristic (traveling in either direction), but remains inside the OUTER
characteristic. One input to AND64 is provided by TLOS3, a second input is supplied by the OUTER, the third
input is energized by NOT62 through OR64. If the output from AND64 lasts for the pickup setting of TLOS4,
TL64 operates and seals in. The output of TLOS4 also provides one input of AND65.
STEP 5:
If Protection Setting 1403:
TRIPIN_OUT
= OUT, tripping is not initiated until the swing has passed through the
OUTER characteristic for the second time. When the OUTER resets, the second input of AND65 is supplied by
NOT63. AND65, through OR65, picks up the out-of-step tripping relay, OST. This output lasts for 50 millisec-
onds (three cycles at 60 Hz) after the OUTER resets, which is the dropout time of TLOS1.
1.9.4 TWO-CHARACTERISTIC OPERATION
Operation with two characteristics instead of three (Protection Setting 1402:
NUMBRCHAR
= 2) is essentially
the same as described above, except that the MIDDLE characteristic and TLOS2 are taken out of the circuit.
Only the OUTER and INNER characteristics are involved in the two characteristic mode of operation.
1.9.5 OUT-OF-STEP OSCILLOGRAPHY CAPTURE
The Out-of-Step Tripping option includes an out-of-step oscillography feature. The OS data file contains the
real and imaginary components of the phase currents and voltages, sampled once per cycle for 180 cycles; 60
pre-trigger samples and 120 post-trigger samples are stored. Data are stored whenever an Out-of-Step Block
(OSB) condition or an Out-of-Step Trip (OST) condition is detected. If both an OSB and OST are detected, the
data is stored based on the OST operation. Only one OS data file is stored in the LPS-O. Once the data is cap-
tured, it will not be overwritten until it is retrieved from the LPS-O or cleared by an OS data reset command.
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