GE D90 Plus Instruction Manual page 211

CHAPTER 7: PROTECTION
Ground distance settings
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D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
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.
Ensure that the
Phase VT Secondary Voltage
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.
GROUPED PROTECTION ELEMENTS
setting is programmed correctly to prevent
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