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CHAPTER 7: PROTECTION CONTROL ELEMENTS
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 289
Pilot-aided schemes
This section contains settings for selecting and configuring protection signaling schemes.
All schemes are available for single-pole tripping applications and can be used with single-
bit, two-bit, or four-bit communications channels. Choices of communications channels
include remote inputs, remote outputs, and telecommunications interfaces.
The D90
Plus
includes six common pilot-aided schemes.
• 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).
• Directional comparison blocking.
• Directional comparison unblocking (DCUB).
Direct under-reaching transfer trip
The direct under-reaching transfer trip (DUTT) scheme uses an under-reaching zone 1
distance element to key transfer trip signals to the remote ends, where on receipt, the
DUTT pilot scheme operates without additional protection supervision. For proper
operation of the scheme, the zone 1 phase and ground distance elements must be
enabled, configured, and set according to the principles of distance relaying.
In single-pole tripping applications, the DUTT scheme uses local fault type identification
provided by the phase selector together with information received from the remote
terminals. The latter may be coded into one, two, or four bits over the communications
channel.
The scheme generates output operands (
DUTT TX1
through
DUTT TX4
) that are used to
transmit the direct under-reaching signals to the remote ends. Choices of communications
channel include remote inputs, remote outputs, and telecommunications interfaces. When
used with telecommunications facilities, the output operands should be assigned to
operate output contacts connected to assert the individual bits at the interface.
To make the scheme a fully operational stand-alone feature, the output operands must be
configured to interface with other relay functions, in particular output contacts. Typically,
the output operands are be programmed to initiate a trip, breaker fail, and autoreclose,
and drive an annunciator indication. When used in conjunction with the trip output
element, the scheme is pre-configured to initiate trip, breaker fail, and single-pole
autoreclose actions.
Select the
Settings > Protection > Control > Pilot Schemes > DUTT Scheme menu item to
access the direct under-reaching transfer trip settings.
Figure 248: DUTT scheme configuration settings