Restricted Earth Fault (87N) Toolkit

Visualizing REF Protection Principles from the SEL-787 Manual

System Configuration: Delta-Wye Transformer

Primary (Δ) A B C Secondary (Y) a b c N

Fault Simulation

a Phase CT (for Ipol) N Neutral CT (for Iop)
Internal Fault External Fault
±85°
0.25 A

Neutral CT (Iop)

0.0 A ∠ 0.0°

Phase CTs (Ipol)

0.0 A ∠ 0.0°

REF Directional Characteristic

Iop relative to Ipol (Fig 4.8, SEL-787 Manual)

Calculated Values

Operate (Iop): 0.00 A

Polarizing (Ipol): 0.00 A

Phase Angle: 0°