GE D90 Plus Instruction Manual page 29

CHAPTER 2: PRODUCT DESCRIPTION
Communication aided (pilot) schemes
Power swing detection
Line pickup
Overvoltage and undervoltage protection
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
For additional information, refer to:
Fault report on page 506
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
communications. This allows transmission of phase selective information for reliable
single-pole tripping if required.
For additional information, refer to:
Pilot-aided schemes on page 289
Communications channels for pilot-aided schemes
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.
For additional information, refer to:
Power swing detect settings
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.
For additional information, refer to:
Line pickup on page 179
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.
For additional information, refer to:
Voltage elements on page 262
on page 657
on page 207
DEVICE OVERVIEW
Plus
built-in power swing
19