There are however some situations that can cause security problems like reverse phase to
phase faults and double phase-to-ground faults during high load periods. To solve these,
additional directional element is used.
For phase-to-ground faults, directional elements using sequence components are very
reliable for directional discrimination. The directional element can be based on one of
following types of polarization:
•
Zero-sequence voltage
•
Negative-sequence voltage
•
Zero-sequence current
These additional directional criteria are evaluated in the Additional distance protection
directional function for ground faults (ZDARDIR).
Zero-sequence voltage polarization is utilizing the phase relation between the zero-
sequence voltage and the zero-sequence current at the location of the protection. The
measurement principle is illustrated in figure
.
- 3V
0
3I
0
AngleRCA
AngleOp
en06000417_ansi.vsd
ANSI06000417 V1 EN
Figure 74:
Principle for zero-sequence voltage polarized additional directional
element
Negative-sequence voltage polarization is utilizing the phase relation between the
negative-sequence voltage and the negative-sequence current at the location of the
protection.
Zero-sequence current polarization is utilizing the phase relation between the zero-
sequence current at the location of the protection and some reference zero-sequence
current, for example, the current in the neutral of a power transformer.
1MRK 506 335-UUS A
Section 6
Impedance protection
163
Technical manual
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