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Contents

  1. Preface ………………………………………………………………………………………………………………. 5
  2. Introduction ……………………………………………………………………………………………………….. 7
  3. Definitions and general approach………………………………………………………………………….. 8
  4. Instantaneous or Definite Time Overcurrent Protection………………………………………… 14
  5. Inverse Time Overcurrent Protection …………………………………………………………………… 15
  6. Distance protection……………………………………………………………………………………………. 17
  7. Transformer Differential protection …………………………………………………………………….. 19
  8. Line Differential protection …………………………………………………………………………………. 21
  9. Generator Differential protection ……………………………………………………………………….. 24
  10. Low Impedance Busbar Protection ………………………………………………………………………. 26
    APPENDIX 1 ………………………………………………………………………………………………………….. 28
    Criteria for CT verification during internal faults ……………………………………………………….. 28
    APPENDIX 2 ………………………………………………………………………………………………………….. 32
    Dimensioning of Current Transformers (CT) for Application in Protection ……………………. 32
    APPENDIX 3 ………………………………………………………………………………………………………….. 47
    Typical X/R values …………………………………………………………………………………………………. 47
    APPENDIX 4 ………………………………………………………………………………………………………….. 49
    Criteria for CT calculation in High Impedance Relays …………………………………………………. 49
    APPENDIX 5 ………………………………………………………………………………………………………….. 54
    Calculation Examples …………………………………………………………………………………………….. 54
    APPENDIX 6 ………………………………………………………………………………………………………….. 57
    Importance of having similar CT characteristics in a Generator Differential protection …. 57
    APPENDIX 7 ………………………………………………………………………………………………………….. 61
    CT Equivalences between IEC and ANSI Standards ……………………………………………………. 61
    APPENDIX 8 ………………………………………………………………………………………………………….. 63
    Conversion in class TPX or equivalent 5P …………………………………………………………………. 63
    APPENDIX 9 ………………………………………………………………………………………………………….. 64
    Questions and answers ………………………………………………………………………………………….. 64
    APPENDIX 10 ………………………………………………………………………………………………………… 83
    Permeability and Saturation …………………………………………………………………………………… 83
    APPENDIX 11 ………………………………………………………………………………………………………… 92
    Terms and Definitions ……………………………………………………………………………………………. 92
    References ………………………………………………………………………………………………………………. 96

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