Table 2 The values range of three-phase directionality factors and differential currents at different fault types and the traditional relay action.
From: Adaptive differential current relay based on form/ripple factors for busbar current signals
Sr. No. | Fault type | The range values of the three phase directionality factors | The range values of the three phase differential currents | Traditional relay action |
|---|---|---|---|---|
1. | Normal operation | DFav = + 1.0 DFbv = + 1.0 DFcv = + 1.0 | ida < Id0 + Ks × ira, idb < Id0 + Ks × irb and idc < Id0 + Ks × irc | Blocking |
2. | External fault without CT saturation condition | DFav = + 1.0 DFbv = + 1.0 DFcv = + 1.0 | ida < Id0 + Ks × ira, idb < Id0 + Ks × irb and idc < Id0 + Ks × irc | Blocking |
3. | External fault with CT saturation condition | + 1.0 > DFav ≥ 0.0, + 1.0 > DFbv ≥ 0.0, or + 1.0 > DFcv ≥ 0.0 | ida < Id0 + Ks × ira, idb < Id0 + Ks × irb and idc < Id0 + Ks × irc during the free saturated portions of the secondary currents | The CT saturation may lead to the traditional relay malfunction (Tripping) on severe external faults |
ida ≥ Id0 + Ks × ira, idb ≥ Id0 + Ks × irb or idc ≥ Id0 + Ks × irc during the saturated/distorted portions of secondary currents | ||||
4. | Internal fault without CT saturation condition | 0.0 > DFav ≥ -1.0, 0.0 > DFbv ≥ -1.0, or 0.0 > DFcv ≥ -1.0 | ida ≥ Id0 + Ks × ira, idb ≥ Id0 + Ks × irb or idc ≥ Id0 + Ks × irc | Tripping |
5. | Internal fault with CT saturation condition | 0.0 > DFav ≥ -1.0, 0.0 > DFbv ≥ -1.0, or 0.0 > DFcv ≥ -1.0 | ida ≥ Id0 + Ks × ira, idb ≥ Id0 + Ks × irb or idc ≥ Id0 + Ks × irc during the free saturated portions of the secondary currents | The presence of harmonics (the DC components, CT saturation, or both together) may delay or prevent the traditional relay operation on severe internal faults |
+ 1.0 > DFav ≥ 0.0, + 1.0 > DFbv ≥ 0.0, or + 1.0 > DFcv ≥ 0.0 | ida < Id0 + Ks × ira, idb < Id0 + Ks × irb or idc < Id0 + Ks × irc during the saturated/distorted portions of secondary currents |
