Basler Electric BE1-51/27R - Manual (Page 62)

56 9137200999 Rev F
Figure 35. Relay Signals and Current Pickup Example for 3-Phase Fault (X
E
=0.65 X”
D
)
Figure 36 shows an example similar to Figure 35, but the higher external reactance (X
E
= 2X"
D
) to the fault
develops a higher restraint voltage. In Figure 36, the shaded area of the graph where pickup exceeds 25
percent of nominal is much larger than the shaded area in Figure 35. (This is the area where the relay
operates slower.) If we assume a fixed 25 percent of nominal pickup current, a significant margin in the
time coordination with external protection is added, although the log scale tends to exaggerate this effect.
Figure 36. Relay Signals and Current Pickup Example for 3-Phase Fault (X
E
=2 X”
D
)
Tests and Adjustments BE1-51/27R