Figure 160: Ost Setting Determination For The Positive Sequence Resistive Component Ost R5 - GE MiCOM P40 Agile Technical Manual

Single breaker current differential (with distance)
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P543i/P545i
OST trip
OST R6'
Resistive reverse (R')

Figure 160: OST setting determination for the positive sequence resistive component OST R5

Z
is the total system positive sequence impedance equal to Z
T
positive sequence impedances at the sending and receiving ends and Z
θ is the angular difference between the voltages at the sending and receiving ends beyond which no system
recovery is possible.
To determine the settings for OST, the minimum inner resistive reach of OST R5 (R5min) needs to be calculated.
The figure above shows that:
R5min = (Z
/2) / tan(θ/2
T
Next the maximum (limit value) for the outer resistive reach OST R6 (R6 max) needs to be calculated. Referring to
the figure below, point A must not overlap with the load area for the worst assumed power factor of 0.85 and the
lowest possible Z
angle α.
T
P54x1i-TM-EN-1
+jX
OST Z6
OST Z5
Z
T
Z
R
Z
L
OST R5'
OST R5
Z
S
OST Z5'
OST Z6'
Zone 6
Zone 5
Predictive OST trip
θ
α
OST R6
Resistive forward (+R)
+ Z
+ Z
, where Z
S
L
R
is the positive sequence line impedance.
L
Chapter 10 - Power Swing Functions
and Z
are the equivalent
S
R
V02763
287

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