Siemens siprotec SJ62 User Manual page 100

Direction Determi-
nation with Zero-
Sequence System
or Ground Quanti-
ties
Direction Determi-
nation with Nega-
tive Sequence
System
Cross-Polarized
Reference Voltages
for Direction Deter-
mination
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
time period (2 cycles), the detected direction is saved, as long as no sufficient mea-
suring voltage is available. When closing onto a fault, if no stored voltage values exist
in the buffer, the relay element will trip. In all other cases the voltage magnitude will be
sufficient for determining the direction.
Two methods are available to determine the direction for the directional ground fault
element.
For the directional ground fault elements, direction can be determined by comparing
the zero sequence system quantities. In the current path, the I
the transformer neutral current is connected to the device. Otherwise the device cal-
culates the ground current from the sum of the three phase currents. In the voltage
path, the displacement voltage V
erwise the device calculates as reference voltage the zero-sequence voltage 3 · V
from the sum of the three phase voltages. If the magnitude of V
cient to determine direction, the direction is undefined. Then the directional ground el-
ements will not initiate a trip signal. If the current I
because only two current transformers are utilized or the current transformers are con-
nected in an open delta configuration, then the directional ground elements will not be
able to function. The latter is only permitted in ungrounded systems.
Here, the negative sequence current and as reference voltage the negative sequence
voltage are used for the direction determination. This is advantageous if the zero se-
quence is influenced via a parallel line or if the zero voltage becomes very small due
to unfavorable zero impedances. The negative sequence system is calculated from
the individual voltages and currents. As with the use of the zero sequence values, a
direction determination is carried out if the values necessary for the direction determi-
nation have exceeded a minimum threshold. Otherwise the direction is undetermined.
A 2-pole short circuit is detected by two directional phase elements, i.e. the directional
phase elements associated with the faulted phases. A single-pole fault (ground fault)
is detected by the directional ground element, and may be detected by the directional
phase elements associated with the faulted phases if the magnitude of the fault current
is sufficient to pickup the directional element. For the directional ground fault elements,
naturally, pre-described connection requirements must be fulfilled.
For a phase-to-ground fault, the voltage (reference voltage) used by the directional
phase element of the faulted phase is 90° out of phase with the phase-to-ground
voltage of the faulted phase at the relay location (see Figure 2-23). With phase-to-
phase faults, the angle between the unfaulted voltages (reference voltages) and the
fault voltages can be between 90° (remote fault) and 60° (close-up fault) depending
on the degree of collapse of the fault voltages.
2.3 Directional Overcurrent Protection 67, 67N
is used as reference voltage, if it is connected. Oth-
N
cannot be determined, e.g.
0
current is valid, when
N
0
or 3 · V is not suffi-
N 0
98