Feeder protection: distance systems

Feeder protection: distance systems

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The principle of impedance measurement and the engineering of basic impedance measuring elements into schemes of distance protection whether they be switched, nonswitched, carrier-aided etc., has always formed a very important part of power system feeder protection. The importance of its role is reflected in the fact that this form of protection more than any other has long been the subject of rapid and continuous development necessary to meet the ever increasing demands typical of modern power systems. Such development has, for many years, seen little change in operating principle (discounting more recent computer-based techniques) although the methods of implementation vary considerably largely because of the degrees of freedom allowed by modern developments in technologies of all kinds (component, computer, communications etc.). However, although implementation of the principle is subject to continuous change through development, there are basic design concepts which are almost universally established and which are important in understanding the principles of application. For this reason, this chapter is concerned mainly with the theoretical basis for design of distance protection and the more fundamental aspects of application.

Chapter Contents:

  • 9.1 Introduction
  • 9.2 Historical
  • 9.3 Operating principles
  • 9.3.1 Impedance measurement
  • 9.3.2 Derivation of basic measuring quantities
  • 9.4 Impedance-measuring elements (comparators) and their characteristics
  • 9.4.1 Presentation of characteristics
  • 9.4.2 Derivation of relay characteristics
  • 9.4.3 Equivalent of amplitude and phase comparators
  • 9.4.4 Basic range of impedance characteristics
  • 9.4.5 Measuring characteristics of relay schemes
  • 9.4.6 Mho characteristics
  • 9.4.7 Practical polarised mho characteristic
  • 9.5 Development of comparators
  • 9.5.1 Induction cup
  • 9.5.2 Rectifier bridge moving coil
  • 9.5.3 Electronic relays: introduction
  • 9.5.4 Comparator development
  • 9.5.5 Practical realisation of static phase comparators
  • 9.6 More complex relaying characteristics
  • 9.6.1 Basis for shaped polar characteristics
  • 9.6.2 Change of angular criterion
  • 9.6.3 Multicomparator schemes
  • 9.6.4 Multi-input comparators
  • 9.6.5 Alternative characteristics
  • 9.7 Presentation of performance
  • 9.7.1 Requirements
  • 9.7.2 Display of measuring accuracy
  • 9.7.3 Display of operating time
  • 9.7.4 Application of contour timing curves
  • 9.7.5 Alternative methods of presentation
  • 9.7.6 Steady-state performance presentation
  • 9.7.7 Dynamic polar characteristics
  • 9.8 Switched and polyphase distance protection
  • 9.8.1 Introduction
  • 9.8.2 Switched distance protection
  • 9.8.3 Polyphase distance protection
  • 9.9 Distance protection schemes based on information links
  • 9.9.1 General
  • 9.9.2 Tripping schemes
  • Direct intertrip
  • Permissive intertrip-underreaching schemes
  • Permissive intertrip-overeaching systems
  • 9.9.3 Blocking schemes
  • Distance protection blocking scheme
  • Directional comparison
  • 9.10 Practical considerations in the application of distance protection
  • 9.10.1 Fault resistance
  • 9.10.2 Measuring errors
  • 9.10.3 Healthy phase relays
  • 9.10.4 Load encroachment
  • 9.10.5 Power swing encroachment
  • 9.10.6 Line check
  • 9.10.7 Voltage transformer supervision
  • 9.11 Trends in distance protection development
  • 9.12 Bibliography

Inspec keywords: relay protection; electric impedance measurement; power system protection

Other keywords: distance feeder protection; impedance measurement; power system feeder protection

Subjects: Power system protection

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