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2.3 PROTECTION SETTINGS
2.
If the circuit breaker is not capable of interrupting when the systems are nearly 180× apart, set TRIPIN_OUT = OUT.
2
1704: FWDREACH - OST Forward Reach
For the simple system shown above in Figure 2–16: OST REACH CHARACTERISTIC, set the forward reach long enough
to include the line plus the source at the remote end of the line; that is, FWDREACH > Zb + Zc
1705: REVREACH: - OST Reverse Reach
For the system shown above in Figure 2–16: OST REACH CHARACTERISTIC, set the reverse reach to include the source
behind the ALPS; that is, REVREACH > Za
1706: OUTER: Outer Characteristic Angle
1707: MIDDLE - Middle Characteristic Angle
1708: 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 factors are used in deter-
mining 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 2–16: 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°. For example if angle D = 50°, set OUTER = 70°.
The INNER characteristic angle (angle C in figure above) sets the point at which an out-of-step trip will be initiated and is
dependent on the angle beyond which the system cannot 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°.
2-40
Za
Zb
ALPS
X
Zf
Zc
Zb
C
B
Zr
Za
Figure 2–16: OST REACH CHARACTERISTIC
ALPS Advanced Line Protection System
2 CALCULATION OF SETTINGS
Zc
A
Zload
D
R
GE Power Management
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