Whichever power swing detector is responsible for applying PSB, the removal of PSB is defined by two settings –
the PSB Reset Delay and (if an unblocking philosophy is employed) the PSB Unblock dly.
3.6.1 SETTING THE RESISTIVE LIMITS
The Zone 7 quadrilateral should encompass all distance elements to be blocked during a power swing condition.
The Zone 8 quadrilateral should be set smaller than the minimum possible load impedance. The security margin
for both conditions should be at least 20%, also a margin of at least 10% should be provided between Zone 7 and
Zone 8:
R8 > 1.1(R7)
We recommend setting the magnitudes of R7’ and R8’ equal to R7 and R8 respectively:
R7’ = -R7, R8’ = -R8.
V02750
Zone 8
Zone 7
Resistive forward (+R)Resistive reverse (R’)
Maximum Load
+jX
½ Rx Ph. Resistive
Distance zones to be blocked
(only phase-to-phase)
Figure 124: Setting the resistive reaches
3.6.2
SETTING THE REACTIVE LIMITS
The inner Zone 7 should be set in excess of total impedance Z
T
, which include local source impedance Z
S
, line
impedance Z
L
and remote source impedance Z
R
. Only positive sequence impedances should be considered. The
security margin for this condition should be at least 20%. The recommended margin between Z7 and Z8 settings is
10%:
Z8 = 1.1(Z7)
We recommend setting the magnitudes of Z7’ and Z8’ equal to Z7 and Z8 respectively
Z7’ = -Z7, Z8’ = -Z8
The angle Alpha should be set equal to the angle of the total impedance Z
T
:
a
=
Ð
Z
T
Chapter 10 - Power Swing Functions P446SV
238 P446SV-TM-EN-1
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