7UT51 v3 Contents
PRIM-2330C 5
5.4 Trip Characteristic.......................................................................................................................................71
5.4.1 Trip Characteristic Settings......................................................................................................................... 72
5.5 Through-Fault Restraint..............................................................................................................................74
5.6 Blocking by Frequency Variance ................................................................................................................ 74
5.7 Time Delays................................................................................................................................................75
5.8 Events and Actions.....................................................................................................................................75
6 Bus Differential Protection (87B) ................................................................................................. 79
6.1 Method of Operation...................................................................................................................................79
6.2 Describing the Protected Bus .....................................................................................................................79
6.2.1 Type of Protected Object ............................................................................................................................79
6.2.2 System Frequency......................................................................................................................................80
6.2.3 Rated Nominal Current...............................................................................................................................80
6.2.4 Normal Operational Status .........................................................................................................................80
6.3 Describing the CT Scheme......................................................................................................................... 81
6.3.1 Nominal Primary Rating of CTs ..................................................................................................................81
6.3.2 Nominal Secondary Rating of CTs..............................................................................................................81
6.3.3 Orientation of CTs.......................................................................................................................................81
6.4 Trip Characteristic.......................................................................................................................................83
6.4.1 Trip Characteristic Settings......................................................................................................................... 84
6.5 Through-Fault Restraint..............................................................................................................................85
6.6 CT Circuit Monitoring.................................................................................................................................. 86
6.7 Time Delays................................................................................................................................................86
6.8 Events and Actions.....................................................................................................................................86
7 Ground Differential Protection (87N) ...........................................................................................91
7.1 Calculated Quantities .................................................................................................................................92
7.2 Trip Decision...............................................................................................................................................93
7.3 Second Harmonic Restraint........................................................................................................................ 94
7.4 Normal Operational Status .........................................................................................................................95
7.5 Pickup Level and Limit Angle .....................................................................................................................95
7.6 Harmonic Restraint.....................................................................................................................................96
7.7 Time Delays................................................................................................................................................96
7.8 Events and Actions.....................................................................................................................................96
8 Time Overcurrent Protection (50HS and 50/51) .......................................................................... 99
8.1 Method of Operation...................................................................................................................................99
8.2 Normal Operational Status .........................................................................................................................99
8.3 High-Set Element (50HS).........................................................................................................................100
8.4 Overcurrent Element (50 or 51)................................................................................................................100
8.4.1 Definite Time Element (50) ....................................................................................................................... 101
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