GE D90 Plus Instruction Manual page 29

CHAPTER 2: PRODUCT DESCRIPTION
Power swing detection
Line pickup
Overvoltage and undervoltage protection
Overfrequency and underfrequency protection
Overcurrent functions
Autoreclose
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
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
Plus
D90 can be used to initiate a local trip as well as a remote trip using direct transfer trip.
Plus
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.
Plus
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.
• Instantaneous and timed overcurrent elements for phase, neutral, ground, and
negative-sequence protection.
• Directional supervision is available for phase, neutral, and negative-sequence
elements.
• Time overcurrent elements can individually be set to use IEEE, IEC, or custom
FlexCurves™.
Plus
The D90 provides multi-shot autoreclosing for single-pole or three-pole autoreclose on
all types of faults with independently programmable dead times for each shot.
Autoreclosing also can be dynamically blocked by user programmable logic. Four different
autoreclose modes are available enabling the users to select the reclosing mode of their
practice.
DEVICE OVERVIEW
Plus
built-in power swing
Plus
, flexible special protection
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