GE D90 Plus Instruction Manual page 27

CHAPTER 2: PRODUCT DESCRIPTION
Fault locator
Communication aided (pilot) schemes
Power swing detection
Line pickup
Overvoltage and undervoltage protection
Overfrequency and underfrequency protection
Overcurrent functions
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
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).
All communication-aided schemes can be programmed for single-bit, two-bit, or four-bit
user communications. This allows transmission of phase selective information for reliable
single-pole tripping if required.
Dynamic transients in the power system due to short-circuits, circuit switching, or load
fluctuations can travel across the power network as power swings characterized by
fluctuating currents and voltages. This can result in unwanted tripping since distance
elements can respond to these power swings as faults. The D90
detection element provides both power swing blocking and out-of-step tripping functions.
The element measures the positive sequence apparent impedance and traces its locus
with respect to either a two or three step user selectable mho or quadrilateral operating
characteristics.
The line pickup feature uses a combination of undercurrent and undervoltage to identify a
line that has been de-energized (line end open). Three instantaneous overcurrent elements
are used to identify a previously de-energized line that has been closed onto a fault.
Long lines under lightly loaded conditions or no-load may experience voltages exceeding
the rated per unit voltage level of the line. The phase overvoltage element of the
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D90 can be used to initiate a local trip as well as a remote trip using direct transfer trip.
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The D90 also provides additional voltage functions including neutral overvoltage,
negative-sequence overvoltage, and phase undervoltage.
The multiple stages of under and over frequency elements can be used to initiate load
shedding or remedial actions schemes or frequency-based load restoration schemes
during lack of generation in the network or due to sudden load drops. When combined
with the advanced automation capabilities of the D90
schemes can be built.
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The D90 provides overcurrent functions for phase, neutral, and ground which can run
parallel with distance protection or can be programmed to provide primary protection
under conditions when distance elements are blocked during fuse-failure conditions.
DEVICE OVERVIEW
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built-in power swing
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, flexible special protection
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