Date Code 20111215 Reference Manual SEL-421 Relay
Section 1
R.Reference Manual
Protection Functions
This section provides a detailed explanation for each of the many SEL-421
Relay protection functions. Each subsection provides an explanation of the
function, along with a list of the corresponding settings and Relay Word bits.
Logic diagrams and other figures are included.
Functions discussed in this section are listed below.
➤ Current and Voltage Source Selection on page R.1.2
➤ Frequency Estimation on page R.1.15
➤ Time-Error Calculation on page R.1.16
➤ Fault Location on page R.1.18
➤ Open Phase Detection Logic on page R.1.20
➤ Pole Open Logic on page R.1.20
➤ Loss-of-Potential Logic on page R.1.23
➤ Fault Type Identification Selection Logic on page R.1.27
➤ Ground Directional Element on page R.1.27
➤ Phase and Negative-Sequence Directional Elements on
page R.1.38
➤ Directionality on page R.1.39
➤ CVT Transient Detection on page R.1.40
➤ Series-Compensation Line Logic on page R.1.41
➤ Load-Encroachment Logic on page R.1.42
➤ Out-of-Step Logic on page R.1.43
➤ Mho Ground Distance Elements on page R.1.49
➤ Quadrilateral Ground Distance Elements on page R.1.54
➤ Mho Phase Distance Elements on page R.1.58
➤ Zone Time Delay on page R.1.61
➤ Instantaneous Line Overcurrent Elements on page R.1.64
➤ Inverse-Time Overcurrent Elements on page R.1.70
➤ Switch-Onto-Fault Logic on page R.1.84
➤ Communications-Assisted Tripping Logic on page R.1.87
➤ Directional Comparison Blocking Scheme on page R.1.88
➤ Permissive Overreaching Transfer Tripping Scheme on
page R.1.91
➤ Directional Comparison Unblocking Scheme Logic on
page R.1.100
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