GE D90 Plus Instruction Manual page 28

DEVICE OVERVIEW
Application to series-compensated lines
In-zone transformer compensation
Load encroachment
Fault locator
Communication aided (pilot) schemes
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The D90 provides enhanced stability and security by employing an adaptive distance
reach control to cope with the overreaching and sub-synchronous oscillations when
applied to, or in the vicinity of, series compensated lines. For directional integrity the relay
uses memory voltage polarization and a multi-input comparator is used to deal with
current inversion issues in series compensated lines.
Phase distance elements in the D90
of three-phase wye or delta transformers, allowing application of the D90
protection on generators. VTs and CTs can be installed independently of each other on
either side of the power transformer. The relay automatically compensates for transformer
connections, to guarantee accurate reach for any type of fault.
The reliable load encroachment feature offers excellent discrimination between keep
loading conditions and fault conditions especially for long lines under heavy loads by
supervising the distance elements or any overcurrent element. This prevents unwarranted
tripping under heavy line load conditions and enables optimum operation of the line while
meeting regulatory requirements for the loading.
The following diagram illustrates distance quadrilateral characteristics supervised by load
encroachment function.
Figure 8: Load encroachment characteristic example
The integrated fault locator provides distance to fault in kilometers or miles.
Plus
The D90 supports different pilot scheme functions for fast fault clearance for any faults
within the protected line. The following types of pilot-aided schemes are available.
• Direct under-reaching transfer trip (DUTT).
• Permissive under-reaching transfer trip (PUTT).
• Permissive over-reaching transfer trip (POTT).
• Hybrid permissive over-reaching transfer trip (hybrid POTT) with permissive echo and
transient blocking logic.
• Directional comparison blocking scheme.
• Directional comparison unblocking scheme (DCUB).
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can be used to detect faults through different types
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 2: PRODUCT DESCRIPTION
Plus
for backup