CHAPTER 8: APPLICATION OF SETTINGS
INSTANTANEOUS ELEMENTS
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
8-25
8
The L90 ensures stability in such a case by removing the zero-sequence current from the phase currents prior to
calculating the operating and restraining signals (
SETTINGS
SYSTEM SETUP
L90 POWER SYSTEM
ZERO-SEQ
CURRENT REMOVAL
is “Enabled”). Removing the zero-sequence component from the phase currents can cause the L90 to
overtrip healthy phases on internal ground fault. This is not a limitation, as the single-pole tripping is not recommended for
lines with tapped transformers.
8.8 Instantaneous elements
8.8.1 Instantaneous element error during L90 synchronization
Two or three L90 relays are synchronized to each other and to system frequency to provide digital differential protection
and accurate measurements for other protection and control functions. When an L90 system starts up, the relays adjust
their frequency aggressively to bring all relays into synchronization with the system quickly. The tracking frequency can
differ from nominal (or system frequency) by a few hertz, especially during the first second of synchronization. The 87L
function is blocked during synchronization; therefore, the difference between system frequency and relay sampling
frequency does not affect 87L function. However, instantaneous elements have additional error caused by the sensitivity of
Fourier phasor estimation to the difference between signal frequency and tracking frequency.
To secure instantaneous element operation, it is recommended either to use FlexLogic as shown here to block the
instantaneous elements during synchronization, or to use a different setting group with more conservative pickup for this
brief interval.
Figure 8-8: FlexLogic to block instantaneous element during 87L startup
The elements must be treated selectively. If, for example, the phase undervoltage setting includes margin sufficient to
accommodate the maximum additional error on startup, blocking or delay are not needed for phase undervoltage.
Similarly, if the phase instantaneous overcurrent setting has sufficient margin, blocking is not needed. Note that significant
zero-sequence and negative-sequence current or voltage error do not appear during L90 startup, therefore all elements
using these quantities are safe.
The table indicates the maximum error and recommended block durations for different elements.
Table 8-1: Maximum error and recommended block duration
Element
Maximum error on startup (operate
signal vs. setting)
Recommended block duration
Phase undervoltage
18%
0.7 seconds
Phase instantaneous overcurrent
9%
0.5 seconds
Ground distance zone 1
7%
Not needed
Phase distance zone 1
4%
Not needed
Содержание L90
Страница 14: ...1 4 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL FOR FURTHER ASSISTANCE CHAPTER 1 INTRODUCTION 1 ...
Страница 68: ...2 54 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL SPECIFICATIONS CHAPTER 2 PRODUCT DESCRIPTION 2 ...
Страница 136: ...3 68 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL CONNECT TO D400 GATEWAY CHAPTER 3 INSTALLATION 3 ...
Страница 224: ...4 88 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL FLEXLOGIC DESIGN USING ENGINEER CHAPTER 4 INTERFACES 4 ...
Страница 692: ...6 36 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL PRODUCT INFORMATION CHAPTER 6 ACTUAL VALUES 6 ...
Страница 708: ...7 16 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL TARGETS MENU CHAPTER 7 COMMANDS AND TARGETS 7 ...
Страница 742: ...9 6 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL TESTING CHAPTER 9 COMMISSIONING 9 ...
Страница 804: ...10 62 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL FAULT LOCATOR CHAPTER 10 THEORY OF OPERATION 10 ...
Страница 872: ...C 6 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL COMMAND LINE INTERFACE APPENDIX C COMMAND LINE INTERFACE C ...
Страница 878: ...D 6 L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL REVISION HISTORY APPENDIX D MISCELLANEOUS D ...
Страница 882: ...iv L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL ABBREVIATIONS ...
Страница 900: ...xviii L90 LINE CURRENT DIFFERENTIAL SYSTEM INSTRUCTION MANUAL INDEX ...