ABB REC650 - Calculating Settings for Four Step Residual Overcurrent Protection Zero or Negative Sequence Direction HV-Side EF4 PTOC (51 N;67 N)

difference between the inverse time curves is 0.4 s. With the setting TD4= 0.15 the
time margin between the characteristics is about 0.4 s as shown in figure 9.
IEC09000453 V1 EN
Figure 9: Inverse time operation characteristics for selectivity
3.1.6 Calculating settings for four step residual overcurrent
protection, zero or negative sequence direction HV-side
EF4PTOC (51N/67N)
The protection is fed from the 145 kV neutral point of the current transformer.
Section 3 1MRK 511 286-UUS A
REC650 setting examples
50
Application manual