5 Settings Group Selection 69
Chapter 6 Current Protection Functions 71
1 Chapter Overview 73
2 Thermal Overload Protection 74
2.1 Thermal Overload Protection 74
2.2 Thermal Replica 75
2.3 Thermal Trip 76
2.4 User programmable curve for thermal overload protection 78
2.5 Application Notes 78
2.5.1 Thermal Overload Setting Guidelines 78
3 Overcurrent Protection Principles 84
3.1 IDMT Characteristics 84
3.1.1 IEC 60255 IDMT Curves 85
3.1.2 European Standards 87
3.1.3 North American Standards 88
3.1.4 IEC and IEEE Inverse Curves 90
3.1.5 Differences Between the North american and European Standards 91
3.1.6 Programmable Curves 91
3.2 Principles of Implementation 91
3.2.1 Timer Hold Facility 92
4 Phase Overcurrent Protection 94
4.1 Phase Overcurrent Protection Implementation 94
4.2 Non-Directional Overcurrent Logic 95
4.3 Directional Element 96
4.3.1 Directional Overcurrent Logic 98
4.4 Application Notes 98
4.4.1 Short Circuit Protection 98
5 Current Setting Threshold Selection 101
6 Negative Sequence Overcurrent Protection 102
6.1 Negative Sequence Overcurrent Protection Implementation 102
6.2 Non-Directional Negative Sequence Overcurrent Logic 103
6.3 Directional Element 103
6.3.1 Directional Negative Sequence Overcurrent Logic 104
6.4 Phase Rotation 104
6.5 Application Notes 105
6.5.1 Negative Sequence Protection 105
7 Earth Fault Protection 109
7.1 Earth Fault Protection Elements 109
7.2 Non-directional Earth Fault Logic 110
7.3 IDG Curve 110
7.4 Directional Element 111
7.4.1 Residual Voltage Polarisation 111
7.4.2 Negative Sequence Polarisation 113
7.5 Application Notes 114
7.5.1 Setting Guidelines (Directional Element) 114
7.5.2 Peterson Coil Earthed Systems 115
7.5.3 Setting Guidelines (Compensated networks) 118
7.5.4 Solidly Earthed System 119
7.5.5 Insulated System 120
7.5.6 Resistance Earthed Systems 123
7.5.7 High Resistance Earthing 123
7.5.8 Petersen coil earthed systems 124
7.5.9 Operation of sensitive earth fault element 129
8 Sensitive Earth Fault Protection 130
8.1 SEF Protection Implementation 130
8.2 Non-directional SEF Logic 130
P24xM Contents
P24xM-TM-EN-2.1 iii
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