Additional Distance Protection Directional Function For Ground Faults Zdardir - ABB Relion 670 Series Technical Reference Manual

Section 6
Impedance protection
6.6.2.2
280
• reactance phase C
• direction phase A
• direction phase B
• direction phase C
Additional distance protection directional function for ground faults
ZDARDIR
A Mho element needs a polarizing voltage for its operation. The positive-sequence
memory-polarized elements are generally preferred. The benefits include:
• The greatest amount of expansion for improved resistive coverage. These elements
always expand back to the source.
• Memory action for all fault types. This is very important for close-in three-phase
faults.
• A common polarizing reference for all six distance-measuring loops. This is
important for single-pole tripping, during a pole-open period.
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 143.
1MRK505222-UUS C
Technical reference manual