Numerical Differential Protection

Transcription

1 Numerical Differential Protection Principles and Applications Publicis Corporate Publishing

2 1 Introduction Protection Principle Numerical Differential Protection 9 2 Deflnitions 10 3 Mode of Operation Introduction Basic Principles Current differential protection Biased (stabilised) differential protection Differential Protection with two pilot wire cores Operating characteristics Measuring Circuit for Three Phase Systems Measurement per phase Composite current version High Impedance (HI) Differential Protection Partial Differential Protection 47 4 Measuring Technique Classical Analog Systems Numerical Measuring Technique Acquisition of measured values Differential protection with instantaneous value comparison Differential protection with phasors Additional stabilisation with CT Saturation 60 5 Current Transformers (CTs) Current Transformer Equivalent Circuits Specifications for the Steady State Response of Current Transformers Transient Response of the CT TP Current Transformer Classes Polarity of the CT CT Errors Dimensioning of the CT Interposing CTs 86 6

3 6 Communications Transmission Channels Pilot wires Fibre Optic Cables Line of sight radio links Digital Protection Communication Digital Communication Networks Generator/Motor Differential Protection Generator Differential Protection Motor Differential Protection Transformer Differential Protection Basic Physics Numerical Measured Value Processing High Impedance Differential Protection Devices for Transformer Differential Protection Application Examples for Transformer Protection Line Differential Protection Three Core Pilot Wire (Triplet) Differential Protection Two Core (Twisted Pair) Pilot Wire Differential Protection Feeder Differential Protection with Digital Communication Phase Comparison Protection with Digital Communication Differential Protection of Feeders Including Transformers Protection of transformer feeders Differential protection for feeders with tee-offs (tapped lines) Busbar Differential Protection Low Impedance Busbar Differential Protection Partially numerical busbar differential protection 7SS Fully-numerical busbar protection 7SS Response of the Numerical Busbar Protection in the Case of CT Saturation and the Demands Placed on CT Dimension High-Impedance Busbar Protection Relay Design Commissioning and Maintenance Commissioning Maintenance 248 Literature 249 Addendum 257 Index 258 7

4 Numerical Distance Protection Principles and Applications Publicis Corporate Publishing

5 1 Introduction 11 2 Definitions 13 3 Mode of Operation Fundamentals of distance protection Concept Relay impedance (secondary impedance) Impedance diagram Distance measurement Directional fault discrimination Starting (fault detection) Distance zones (steps) Zone- and timer-control Switched and non-switched distance protection Distance protection with signalling Channels Power swing blocking, power swing tripping (out of step protection) Distance protection with automatic reclosure Distance to fault locator Grading chart Numerical distance measurement Definition of the fault loop Determination of the loop impedance Numerical impedance computation Numerical direction determination (polarisation) Direction determination with fault loop voltage (seif polarisation) Direction determination with healthy phase voltages (cross-polarisation) Directional characteristic in the impedance plane Selection of the cross polarisation voltage Influence of load transfer Implementation of voltage-memory(-ies) Adaptive directional determination Circular characteristics with numerical technology MHO-circle PolarisedMHO-characteristic Load influence on polarised MHO-circles MHO-circle with voltage memory 130 7

6 3.5 Distance measurement, Influencing quantities Fault resistance Intermediate infeeds Parallel lines Distance protection for transformers Non-symmetry of the line Series-compensation Device design Intelligent electronic devices (IEDs) Mechanical design Relay Communications Integrated functions Relay terminal connections Relay Operation Application General aspects Application criteria Shortest line length Tripping time Teleprotection, choice of technique Instrument transformer requirements Distance protection in the distribution System General Distance protection in isolated or compensated Systems Distance protection in distribution networks with low impedance star-point earthing Distance protection in industrial networks Distance protection in transmission networks Generals aspects Protection concepts High-voltage overhead lines EHV-line /2 circuit-breaker substations Ring busbar Double circuit line Three-terminal line Series-compensated lines Protection settings General aspects Fault detection (3rd Zone) Fault detection methods and setting philosohies Security of the fault detection Relay (Line) loadability 294 8

7 6.2.4 Phase-selectivity Setting of the U-I-j fault detection Setting of the impedance fault detection Setting of the distance zones Reach (X-setting) and grading time Are compensation (R-setting) Specifics for the zone settings in cable networks Adjusting the zone reach in case of large R/X-setting Grading of distance zones with different characteristics Setting of the power swing blocking Calculation examples Double cireuit lines in earthed Systems Three terminal line (teed feeders) Commissioning Testing of the protection System Test with load Maintenance Seif monitoring Maintenance strategy Bibliography Technical papers Books Appendix 361 A.l Distance measurement algorithms 361 A.l.l Principle 361 A.l.2 Fourier analysis based technique 362 A.l.3 Transient behaviour 367 A.l.4 Practical application 368 A.l.5 Literature 369 A.2 Calculation with phasors and complex quantities 370 A.2.1 Definitions 370 A.2.2 Calculation with phasors and complex quantities 371 A.3 Fundamentals of symmetrical component analysis 374 A.3.1 Calculation procedure 374 A.3.2 Typical System component data 379 A.3.3 Equivalent circuits and formulas for network reduction 380 A.4 Impedances of overhead lines and cables 383 A.4.1 Single line (transposed) 383 A.4.2 Double cireuit line (transposed) 384 A.4.3 Bündle conduetor 385 A.4.4 Cable impedances 385 9

8 A.5 Reach of back-up zones on parallel lines 387 A.5.1 Phase-to-phase faults 387 A.5.2 Phase-to-earth faults 389 A.6 Tilting of the quadrilateral top line to avoid overreach 398 Index