CHAPTER 7: PROTECTION GROUPED PROTECTION ELEMENTS
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 201
Ground distance settings
The ground mho distance function uses a dynamic 100% memory-polarized mho
characteristic with additional reactance, directional, current, and phase selection
supervising characteristics. The ground quadrilateral distance function is composed of a
reactance characteristic, right and left blinders, and 100% memory-polarized directional,
overcurrent, and phase selection supervising characteristics.
When set to non-directional, the mho function becomes an offset mho with the reverse
reach controlled independently from the forward reach, and all the directional
characteristics removed. When set to non-directional, the quadrilateral function applies a
reactance line in the reverse direction instead of the directional comparators.
The reactance supervision for the mho function uses the zero-sequence current for
polarization. The reactance line of the quadrilateral function uses either zero-sequence or
negative-sequence current as a polarizing quantity. The selection is controlled by a user
setting and depends on the degree of non-homogeneity of the zero-sequence and
negative-sequence equivalent networks.
The directional supervision uses memory voltage as polarizing quantity and both zero- and
negative-sequence currents as operating quantities.
The phase selection supervision restrains the ground elements during double-line-to-
ground faults as they, by the principles of distance relaying, can be inaccurate in such
conditions. Ground distance zones 2 through 5 apply additional zero-sequence directional
supervision.
Each ground distance zone is configured individually through its own setting menu.
Although all ground distance zones can be used as either instantaneous elements (pickup
[PKP] and dropout [DPO] FlexLogic signals) or time-delayed elements (operate [OP]
FlexLogic signals), only zone 1 is intended for the instantaneous under-reaching tripping
mode.
FAST PATH:
Ensure that the Phase VT Secondary Voltage setting is programmed correctly to prevent
improper operation of associated memory action.
Select the Settings > Protection > Elements > Group 1 > Ground Distance menu to open
the ground distance configuration window. There are five zones of ground distance
protection for each setting group.
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