Functions
2.3 Directional Overcurrent Protection 67, 67N
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
108
Direction Determination of Directional Ground Element with Negative Sequence Values
Figure 2-30 shows the treatment of the reference voltage for the directional ground element using the negative
sequence values based on a single-pole ground fault in Phase A. As reference voltage, the negative sequence
system voltage is used, as current for the direction determination, the negative sequence system current, in
which the fault current is displayed. The fault current -3
I
2
is in phase oposition to the fault current
I
scA
and
follows the voltage 3V
2
by the fault angle
ϕ
sc
. The reference voltage is rotated through the setting value
1619
ROTATION ANGLE
. In this case, a rotation of -45°.
Figure 2-30
Rotation of the reference voltage, directional ground element with negative sequence values
The forward area is a range of
±
86° around the rotated reference voltage V
ref, rot
. If the vector of the negative
sequence system current -3
I
2
is in this area, the device detects forward direction.
2.3.9
Reverse Interlocking for Double End Fed Lines
Application Example
The directionality feature of the directional overcurrent protection enables the user to perform reverse interlock-
ing also on double end fed lines using relay element 67-1. It is designed to selectively isolate a faulty line
section (e.g. sections of rings) in high speed, i.e. no long graded times will slow down the process. This scheme
is feasible when the distance between protective relays is not too great and when pilot wires are available for
signal transfer via an auxiliary voltage loop.
For each line, a separate data transfer path is required to facilitate signal transmission in each direction. When
implemented in a closed-circuit connection, disturbances in the communication line are detected and signalled
with time delay. The local system requires a local interlocking bus wire similar to the one described in Subsec-
tion "Reverse Interlocking Bus Protection" for the directional overcurrent protection (Section 2.2).
During a line fault, the device that detects faults in forward (line) direction using the directional relay element
67-1 will block one of the non-directional overcurrent elements (50-1, 50-TOC) of devices in the reverse direc-
tion (at the same busbar) since they should not trip (Figure 2-31). In addition, a message is generated regarding
the fault direction. "Forward" messages are issued when the current threshold of the directional relay element
67-1 is exceeded and directional determination is done. Subsequently, "forward" messages are transmitted to
the device located in reverse direction.
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