GE Power Management LPS-O Line Protection System 2-
27
2 CALCULATION OF SETTINGS 2.3 PROTECTION SETTINGS
2
1406: OUTER: Outer Characteristic Angle
1407: MIDDLE - Middle Characteristic Angle
1408: INNER - Inner Characteristic Angle
These three settings are related and the object is to obtain the maximum difference in angle between the inner
and outer settings. This provides the best opportunity of detecting the fastest possible powers swings. Two fac-
tors are used in determining the outer and inner settings:
1. the maximum load flow across the line which determines the minimum load impedance seen by the relay.
2. the maximum swing angle that the power system can tolerate and beyond which the system cannot
recover; that is, the system becomes unstable.
The
OUTER
characteristic angle setting (angle A in Figure 2–13: OST REACH CHARACTERISTIC above) is
based on the maximum load flow across the system and should be selected so that angle A is always greater
than angle D by at least 20 degrees. For example if angle D = 50
°
, then set
OUTER
= 70
°
.
The
INNER
characteristic angle (angle C in Figure 2–13: OST REACH CHARACTERISTIC above) sets the
point at which an out-of-step trip will be initiated and is dependent on the angle beyond which the system can-
not recover. Select an
INNER
setting such that the system is beyond recovering once the inner characteristic is
entered. Typical settings for
INNER
would be in the 120
°
to 150
°
range.
The
MIDDLE
characteristic angle setting is dependent on the
OUTER
setting and the
INNER
setting, and
should be set approximately halfway between the two. For example if
OUTER
= 70
°
and
INNER
= 150
°
, then
set
MIDDLE
= 110
°
.
1409: TLOS1PU - Coordinating Timer 1 Pickup
1410: TLOS1DO - Coordinating Timer 1 Dropout
1411: TLOS2PU - Coordinating Timer 2 Pickup
1412: TLOS3PU - Coordinating Timer 3 Pickup
1413: TLOS4PU - Coordinating Timer 4 Pickup
These five settings are related to each other with the object being to detect the fastest possible swing and to
produce an OST output in a secure manner. Refer to Figure 2–12: OUT-OF-STEP TRIPPING on page 2–25 for
the out-of-step tripping logic.
The pickup time of TLOS1 establishes the first step in the out-of-step process and sets the time that the swing
must remain between the outer and middle characteristics for the first step to be completed.
TLOS1PU
must
be set less than the time that it takes for the
fastest
swing to travel from the outer to the middle characteristic. If
TRIPIN
_
OUT
is set to OUT, the dropout time of TLOS1 sets the time duration for an out-of-step trip output to
be produced. A minimum setting for
TLOS1DO
of 50 milliseconds is proposed. If
TRIPIN
_
OUT
is set to IN,
then
TLOS1DO
can be set to any setting within its range.
The pickup time of TLOS2 establishes the second step in the out-of-step process and sets the time that the
swing must remain between the middle and inner characteristics for this step to be completed.
TLOS2PU
must
be set less than the time that it takes for the
fastest
swing to travel from the outer to the middle characteristic.
The pickup time of TLOS3 establishes the final step in the out-of-step process and determines the time that the
swing must remain inside of the inner characteristic before the final decision is made to produce an out-of-step
trip. It provides added security to the logic. A minimum setting for
TLOS3PU
of 20 milliseconds is proposed.
2.3.16 NONCRIT_AL
Up to eight of the signals listed in the Index Tables given at the end of this section can be used to produce a
non-critical alarm signal (Index Number 52). This signal, when produced, will always be reported as an event
and it can also be programmed to drive one of the output relays if an external alarm is required.
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