Schweitzer Engineering Laboratories SEL-251 - Page 104

ii Table of Contents Date Code 20000421
SEL-251, -2, -3 Instruction Manual
FIGURES
Figure 5.1: Fuse Saving Using Ground/Residual Elements..................................................................... 5-1
Figure 5.2: Reclosing Cycle for Permanent Fault Beyond Tap Fuse....................................................... 5-2
Figure 5.3: Effect of 52APU and 52ADO Settings on Relay Word Bits 52AT and 52BT...................... 5-3
Figure 5.4: Trip Saving Using Ground/Residual Elements...................................................................... 5-4
Figure 5.5: 50C Delayed by TSPU Time ................................................................................................. 5-6
Figure 5.6: Effect of 52APU and 52ADO Settings on Relay Word Bits 52AT and 52BT...................... 5-7
Figure 5.7: Minimum Response Time Using Ground/Residual Elements............................................. 5-11
Figure 5.8: Phase-To-Ground Fault on Delta-Wye Transformer Secondary......................................... 5-14
Figure 5.9: Phase-To-Phase Fault on Delta-Wye Transformer Secondary............................................ 5-15
Figure 5.10: Input IN5 Qualified by Time TKPU.................................................................................. 5-16
Figure 5.11: Element 27 Qualified by Time TKPU............................................................................... 5-17
Figure 5.12: Underfrequency or Undervoltage Trip Condition Time Duration Limit........................... 5-19
Figure 5.13: Distribution Feeder Relay Backup Scheme....................................................................... 5-21
Figure 5.14: Main/Auxiliary Bus with Bus-Tie Circuit Breaker ........................................................... 5-22
Figure 5.15: Underfrequency Load Shedding and Reclose Initiate Supervision................................... 5-24
Figure 5.16: Timing for Reclose Initiation............................................................................................. 5-24