Fault inception Fault cleared
i (t)
PH1
PH2
t
1
t
2
t
3
t
1
: D i exceeds threshold 1 (5%In), so PH1 and PH2 go high
t
2
: Fault current value appears in 2 cycle buffer . This equals present fault current value so D i is reduced to
zero. PH1 therefore goes low. PH2 remains high because value in PH 2 memory is a stored value .
t
3
: Fault is cleared so PH 2 goes low. PH1 stays low even though there is a new D I, because the absolute
current value is also taken into consideration .
V02770
Figure 150: Phase selector timing for fault condition
Start of
power swing
i (t)
3 cycles
PH1
PH2
t
1
t
2
t
3
t
4
t
5
t1: D i exceeds threshold 1 (5%In), so PH1 and PH2 go high
t
2
: Threshold 2 invoked (10%In). PH2 goes low on account of threshold being increased (from 5%IN to 10%In).
PH1 remains high, because there continues to be a D i
t
3
: Fault inception. D i exceeds threshold 2 (10%In), so PH2 goes high
t4: 2 cycles after fault inception , PH1 goes low
t
5
: Fault cleared, so PH2 goes low
V02771
Figure 151: Phase selector timing for fault during a power swing
Chapter 10 - Power Swing Functions P543i/P545i
274 P54x1i-TM-EN-1
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