GE L90

TABLE OF CONTENTS
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL ix
8.8.1 Instantaneous element error during L90 synchronization.............................8-25
8.9 Phase distance through power transformers ................................................8-26
8.9.1 Phase distance protection .............................................................................................8-26
8.9.2 Example ..................................................................................................................................8-27
9 COMMISSIONING 9.1 Testing......................................................................................................................9-1
9.1.1 Channel testing ..................................................................................................................... 9-1
9.1.2 Clock synchronization tests............................................................................................. 9-2
9.1.3 Current differential .............................................................................................................. 9-3
9.1.4 Local-remote relay tests...................................................................................................9-4
10 THEORY OF
OPERATION
10.1 Overview................................................................................................................10-1
10.1.1 L90 design..............................................................................................................................10-1
10.1.2 L90 architecture..................................................................................................................10-2
10.1.3 Removal of decaying offset...........................................................................................10-2
10.1.4 Phaselet computation......................................................................................................10-2
10.1.5 Disturbance detection......................................................................................................10-3
10.1.6 Fault detection.....................................................................................................................10-3
10.1.7 Ground differential element..........................................................................................10-5
10.1.8 Clock synchronization ......................................................................................................10-6
10.1.9 Frequency tracking and phase locking....................................................................10-6
10.1.10 Frequency detection.........................................................................................................10-7
10.1.11 Phase detection ..................................................................................................................10-8
10.1.12 Phase locking filter..........................................................................................................10-10
10.1.13 Matching phaselets........................................................................................................10-11
10.1.14 Start-up................................................................................................................................10-12
10.1.15 Hardware and communication requirements...................................................10-12
10.1.16 Online estimate of measurement errors..............................................................10-12
10.1.17 CT saturation detection................................................................................................10-13
10.1.18 Charging current compensation..............................................................................10-14
10.1.19 Differential element characteristics .......................................................................10-15
10.1.20 Relay synchronization...................................................................................................10-16
10.2 Operating condition characteristics ..............................................................10-17
10.2.1 Description .........................................................................................................................10-17
10.2.2 Trip decision example ...................................................................................................10-19
10.2.3 Trip decision test..............................................................................................................10-19
10.3 Distance elements .............................................................................................10-20
10.3.1 Introduction........................................................................................................................10-20
10.3.2 Phasor estimation...........................................................................................................10-21
10.3.3 Distance characteristics ..............................................................................................10-21
10.3.4 Fast distance algorithm ...............................................................................................10-26
10.3.5 Memory polarization......................................................................................................10-27
10.3.6 Distance elements analysis........................................................................................10-28
10.4 Phase distance applied to power transformers...........................................10-31
10.4.1 Description .........................................................................................................................10-31
10.4.2 Example ...............................................................................................................................10-35
10.5 Single-pole tripping ...........................................................................................10-37
10.5.1 Overview..............................................................................................................................10-37
10.5.2 Phase selection ................................................................................................................10-40
10.5.3 Communications channels for pilot-aided schemes......................................10-42
10.5.4 Permissive echo signaling...........................................................................................10-48
10.5.5 Pilot scheme / phase selector coordination .......................................................10-49
10.5.6 Cross-country fault example .....................................................................................10-50
10.6 Fault locator........................................................................................................10-51