GE Multilin L90 Line Current Differential System 2-32 PRODUCT DESCRIPTION 2.1 INTRODUCTION22.1.2 FEATURESLINE CURRENT DIFFERENTIAL:• Phase segregated, high-speed digital current differential system.• Overhead and underground AC transmission lines, series compensated lines.• Two-terminal and three-terminal line applications.• Zero-sequence removal for application on lines with tapped transformers connected in a grounded wye on the lineside.• GE phaselets approach based on the Discrete Fourier Transform with 64 samples per cycle and transmitting two time-stamped phaselets per cycle.• Adaptive restraint approach improving sensitivity and accuracy of fault sensing.• Increased security for trip decision using disturbance detector and trip output logic.• Continuous clock synchronization via the distributed synchronization technique.• Increased transient stability through DC decaying offset removal.• Accommodates up to five times CT ratio differences.• Peer-to-peer (master-master) architecture changing to master-slave via DTT (if channel fails) at 64 kbps.• Charging current compensation.• Interfaces direct fiber, multiplexed RS422, IEEE C37.94, and G.703 connections with relay ID check.• Per-phase line differential protection direct transfer trip plus eight user-assigned pilot signals via the communicationschannel.• Secure 32-bit CRC protection against communications errors.• Channel asymmetry (up to 10 ms) compensation using GPS satellite-controlled clock.BACKUP PROTECTION:• DTT provision for pilot schemes.• Five zones of distance protection with six pilot schemes, power swing blocking and out-of-step tripping, line pickup,and load encroachment.• Two-element time overcurrent and two-element instantaneous overcurrent directional phase overcurrent protection.• Two-element time overcurrent and two-element instantaneous overcurrent directional zero-sequence protection.• Two-element time overcurrent and two-element instantaneous overcurrent negative-sequence overcurrent protection.• Undervoltage and overvoltage protection.ADDITIONAL PROTECTION:• Breaker failure protection.• Stub bus protection.• VT and CT supervision.• GE Multilin sources approach allowing grouping of different CTs and VTs from multiple input channels.• Open pole detection.• Breaker trip coil supervision and seal-in of trip command.• FlexLogic allowing creation of user-defined distributed protection and control logic.CONTROL:• One and two breaker configuration for breaker-and-a-half and ring bus schemes, pushbutton control from the relay.• Auto-reclosing and synchrochecking.• Breaker arcing current.
