12 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
PRODUCT DESCRIPTION CHAPTER 2: PRODUCT DESCRIPTION
Communication aided (pilot) schemes
The D90
Plus
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 292
Communications channels for pilot-aided schemes
on page 657
Power swing detection
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
Plus
power swing 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
on page 211
Line pickup
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 183
Overvoltage and undervoltage protection
Long lines under lightly loaded conditions or no-load can experience acceptably voltages
exceeding the rated per unit voltage level of the line. The phase overvoltage element of the
D90
Plus
can be used to initiate a local trip as well as a remote trip using direct transfer trip.
The D90
Plus
also provides additional voltage functions including neutral overvoltage,
negative-sequence overvoltage, and phase undervoltage.
For additional information, refer to:
Voltage elements
on page 265
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