GE D90 Plus - Page 200

190 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
GROUPED PROTECTION ELEMENTS CHAPTER 7: PROTECTION
Figure 166: Memory voltage logic
Impact of memory polarization
The D90
Plus
uses a memorized positive sequence voltage as a polarizing signal in order to
achieve dependable operation for forward faults and secure non-operation for reverse
faults.
The dynamic shift of the characteristic ensures improved directionality, but it also means
that if a backup function is required for a reverse fault on the bus, then it is appropriate to
reverse zone 4 so that a time delayed backup function can be obtained. As mentioned
earlier, it can be beneficial to also avoid extremely large reach settings by setting a remote
backup so that it is reverse looking. This strategy can be beneficial if the reduced reach
enhances the discrimination between the load and fault conditions.
Phase distance
The phase mho distance function uses a dynamic 100% memory-polarized mho
characteristic with additional reactance, directional, and overcurrent supervising
characteristics.
The phase quadrilateral distance function has a reactance characteristic, right and left
blinders, and 100% memory-polarized directional and current supervising characteristics.
When set as “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.
Each phase distance zone is configured individually through its own setting menu. All of
the settings can be independently modified for each of the zones except the common
distance settings specified in the previous section.
The common distance settings must be properly chosen for correct operation of the phase
distance elements.
Although all zones can be used as either instantaneous elements (pickup [PKP] and
dropout [DPO] FlexLogic operands) or time-delayed elements (operate [OP] FlexLogic
operands), only zone 1 is intended for the instantaneous under-reaching tripping mode.
NOTICE
FAST PATH:
Ensure that the Phase VT Secondary Voltage setting is set correctly to prevent improper
operation of the associated memory action.
Select the Settings > Protection > Elements > Group 1 > Phase Distance menu to open
the phase distance configuration window.
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