2 PRODUCT DESCRIPTION
2.2 PILOT CHANNEL RELAYING
2.2.3 LOOPBACK TEST
This option allows the user to test the relay at one terminal of the line by looping the transmitter output to the receiver input;
at the same time, the signal sent to the remote will not change. A local loopback feature is included in the relay to simplify
single ended testing.
2.2.4 DIRECT TRANSFER TRIPPING
The L90 includes provision for sending and receiving a single-pole direct transfer trip (DTT) signal from current differential
protection between the L90 relays at the line terminals using the pilot communications channel. The user may also initiate
an additional eight pilot signals with an L90 communications channel to create trip, block, or signaling logic. A FlexLogic™
operand, an external contact closure, or a signal over the LAN communication channels can be assigned for that logic.
L90 Line Current Differential System