8-2
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CT REQUIREMENTS
CHAPTER 8: APPLICATION OF SETTINGS
8
X/R is primary system reactance / resistance ratio
R
CT
is CT secondary winding resistance
R
L
is AC secondary wiring resistance (one-way)
R
R
is relay burden at rated secondary current
5.
Practically, it is difficult to meet this criteria and avoid saturation completely. The L90 provides several means to
ensure security during an external fault, including dual-slope restraint characteristics, adaptive restraint, and CT
saturation mechanism, allowing the relay to be secure during severe external faults, while maintaining excellent
performance for internal faults. Therefore, knee point voltage requirements with a default 87L settings can be
approximately estimated by the following equation:
V
K
> K
tf
x I
S
x Z
S
Eq. 8-3
where
K
tf
is 2 for system X/R > 20 and K
tf
is 1.5 for system X/R
≤
20
This is however applicable, where CT ratios are the same, CT burdens at both sides of the line are very close, and when just
one CT at each side is used. When CTs are different at both sides (different CT characteristics, CT ratio and burden) or when
more than one CT at each side is used, these equation may not provide correct estimation of the required knee point
voltage.
For this situation GE provides a CT saturation analysis tool, described in the following section.
8.1.2 CT saturation analysis tool
The CT saturation analysis tool is an Excel spreadsheet provided for users to analyze the L90 reliability during CT saturation
caused by an external fault, to investigate the effect of adjusting 87L settings, and to examine the possibility of reducing
the CT requirement.
The tool utilizes the CT model and CT saturation calculation algorithm proposed by the IEEE Power System Relaying
Committee (PSRC), and it simulates the analog/digital signal processing and data calculations in the L90. The figure shows
the interface.
Figure 8-1: CT saturation analysis tool main page
For a system where the CTs are already installed, the CT and system parameters are known. Use the procedure described
in the tool to analyze the L90 security during CT saturation and investigate the effect of adjusting 87L settings.
The CT saturation analysis tool allows you to check the application, knowing CT parameters, fault current levels, and
distribution through all breakers from short circuit studies, and to analyze L90 performance, having an ability to adjust
settings as needed. The tool has all instructions to perform analysis.
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 ...
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