Sel 411L - Figure 3.106 Reset Conditions Logic; Figure 3.107 Type of Power Swings Detected by the DOSB Function

P.3.169
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
Out-of-Step Logic (Zero Settings)
3. The ultra-fast derivative dSCV1_UF will be greater than 0.55
(pu V/cyc) for more than 4 cycles.
4. Either all three poles are open (3PO) or an internal loss-of-
potential (ILOP) occurred.
Figure 3.106 Reset Conditions Logic
The Dependable
Power-Swing
Blocking Function
The dependable PSB detector function asserts the DOSB signal for power-
swing conditions where neither the slope detector nor the swing signature
detector can detect a power swing fast enough. An example of this type of
situation might occur after a slow-clearing fault right behind or at the remote
end of a transmission line on a marginally stable network.
As shown in Figure 3.107, if a close reverse or forward fault clears with a
significant delay, there is a possibility that the network has entered a power
swing. In this case, the Z1 trajectory at the relay may cross into the Zone 2 or
Zone 1 phase-mho characteristic right after the fault clears, but before the
slope detector has detected the power swing. In this case, the phase mho
elements of the relay may issue a trip signal as a result of the power swing and
not because of a real fault. To overcome this problem, the dependable power-
swing detector asserts the DOSB (see Figure 3.101) signal to block the
distance elements until the slope detector has had time to detect a power
swing.
Figure 3.107 Type of Power Swings Detected by the DOSB Function
AND 2
AND 3
C1
OR 4
OR 4
OR 3
OR 6
AND 4
EOOST = I, O, C
Z1 Outside
Zone 7
| SCV1 |
0.85
Z1 Outside
Starter Zone
C2
0.0026
| dSCV1_S |
Z2P
Z3P
Z4P
Z5P
C4
| dSCV1_UF |
0.55
3PO
ILOP
OR 5
T1
0
CYC
30
CYC
T2
0
CYC
10
CYC
T3
0
CYC
4
CYC
RST