GE P444 User Manual

P
44x/EN AP/Hb6
Application Notes
(AP) 5
-80 MiCOM P40 Agile
P442, P444
3.5.1.2 Unblocking / blocking logic with power swing or reversal guard
For double circuit lines, the fault current direction can change in one circuit when circuit
breakers open sequentially to clear the fault on the parallel circuit. The change in current
direction causes the overreaching distance elements to see the fault in the opposite direction
to the direction in which the fault was initially detected. (settings of these elements exceed
150% of the line impedance at each terminal). The race between operation and resetting of
the overreaching distance elements at each line terminal can cause the Permissive
Overreach, and Blocking schemes to trip the healthy line. A system configuration that could
result in current reversals is shown in Figure 54. For a specific fault (see distance scheme for
details) on line L1 close to circuit breaker B, as circuit breaker B trips it causes the direction
of current flow in line L2 to reverse.
A
C
B
D
A B
FaultFault
Strong
source
Weak
source
L1
L2
L1
L2 C D
P3067EN
t2(D)
t2(C)
Note how after circuit breaker B on line L1 opens
the direction of current flow in line L2 is reversed.
Figure 54: Current reversal in double circuit lines
In this case, zones & directionality are modified when the following conditions are met (basic
unblocking / blocking logic in the Figure 55):
• Power swing detection (in this case, power swing detected or unblocking during a
power swing),
• Blocking logic settings during power swing,
• Reversal Guard time-delay (DDB: ‘Reversal Guard’),
• Type of teleprotection scheme.
When zones are blocked during the power swing, those can be unblocked by:
• Start of unblocking logic,
• Unblocking logic enabled for the concerned zone or all zones (setting).
In the next figure, the following acronyms are used
Unblock PS Z1, Z2, Z3, Z4, Zp or Zq: Unblocking of Zone 1 (Z1), Z2, Z3, Z4, Zp or Zq
during a power swing (‘Power swing / Blocking zone’
menu)
0 => Zx blocked during power swing
1 => Zx unblocked during power swing
DDB: Z1,Z1x, Z2, Z3, Z4, Zp, Zq: Fault detected in zone 1, Z1x, 2, 3, 4, p or q and
filtered by blocking/unblocking Power Swing
Z1<ZL
Setting: internal configuration that determines that Z1
is smaller than the length of the line ZL.

GE P444 Specifications

General

Brand	GE
Model	P444
Category	Protection Device
Language	English