GE L90 Instruction Manual page 542

CONTROL ELEMENTS CHAPTER 5: SETTINGS
This scheme uses an under-reaching Zone 1 distance element to key a transfer trip signal(s) to the remote end(s), 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 per rules of distance relaying.
In single-pole tripping applications, the scheme uses local fault type identification provided by the Phase Selector together
with information received from the remote terminal(s). The latter can be coded into one, two, or four bits over the
communications channel.
The scheme generates output operands (DUTT TX1 through TX4) that are used to transmit the direct under-reaching
DUTT
signals to the remote end(s). Choices of communications channel include remote inputs/outputs and telecommunications
interfaces. When used with telecommunications facilities, assign the output operands to operate output contacts
connected to assert the individual bits at the interface.
To make the scheme a fully operational stand-alone feature, the scheme output operands must be configured to interface
with other relay functions, output contacts in particular. Typically, you program the output operands to initiate a trip,
breaker fail, and autoreclose, and drive a user-programmable LED as per user application. When used in conjunction with
the trip output element, the scheme is pre-configured to initiate trip, breaker fail, and single-pole autoreclose actions.
— This setting allows the user to assign any FlexLogic operand to block the scheme. Contact inputs
DUTT SCHEME BLOCK
from a pilot cut-out switch are typically used for this purpose.
— The output FlexLogic operand (DUTT OP) is produced according to the DUTT scheme logic. A seal-in
DUTT SEAL-IN DELAY
time delay is applied to this operand for coping with noisy communication channels such as a power line carrier. The
DUTT
is a minimum guaranteed duration of the pulse. As this operand activates the Trip Table of the DUTT
SEAL-IN DELAY
DUTT OP
scheme, the trip operands A, B, C, and are sealed-in for the same period of time.
DUTT TRIP 3P
— This setting specifies the number of bits available on the communications channel. With only one
DUTT NO OF COMM BITS
bit available, the scheme sends the direct under-reaching transfer trip command on bit number 1 (DUTT TX1 operand) and
responds to the direct trip command received on bit number 1 (DUTT RX1 setting). The scheme uses only local fault type
5
identification provided by the Phase Selector to assert the output operands A, B, C, and 3P.
DUTT TRIP
through — These settings allow the user to select the FlexLogic operands that represent the receive
DUTT RX1 DUTT RX4
signals for the scheme. Typically input contacts interfacing with a signaling system are used.
The DUTT scheme requires a secure and dependable signaling system. For this reason, a series/parallel combination of
receive signal "contacts" is often used. This is accomplished by using a multi-bit communications system to transmit
redundant copies of the signal (often via different paths) and building appropriate security logic (such as series (AND
TX
gate) or 2-out-of-3 voting logic) with FlexLogic. The settings should be associated with the final (secure) TX
DUTT RX1(4)
signals.
In single-bit applications, must be used. In two-bit applications, and must be used. In four-bit
DUTT RX1 DUTT RX1 DUTT RX2
applications, , , , and must be used. In multi-terminal applications, connect the RX
DUTT RX1 DUTT RX2 DUTT RX3 DUTT RX4
signals from two or more remote terminals through OR gates in the FlexLogic, and configure the resulting signals as the
inputs
DUTT RX
5-356 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL