GE L90 Instruction Manual page 20

PILOT CHANNEL RELAYING
If a slave L90 issues a trip from one of its backup functions, it can send a transfer trip signal to its master and other slave
relays if such option is designated. Because a slave cannot communicate with all the relays in the differential scheme, the
master then "broadcasts" the direct transfer trip (DTT) signal to all other terminals.
The slave L90 performs the following functions:
• Samples currents and voltages
• Removes DC offset from the current via the mimic algorithm
• Creates phaselets
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• Calculates sum of squares data
• Transmits current data to all master L90 relays
• Performs all local relaying functions
• Receives current differential DTT and Direct Input signals from all other L90 relays
• Transmits direct output signals to all communicating relays
• Sends synchronization information of local clock to all other L90 clocks
The master L90 relay performs the following functions:
• Performs all functions of a slave L90
• Receives current phasor information from all relays
• Performs the current differential algorithm
• Sends a current differential DTT signal to all L90 relays on the protected line
In the peer-to-peer mode, all L90 relays act as masters.
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CHAPTER 2: PRODUCT DESCRIPTION
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL