Zone-2 Distance Settings; Zone-3 Distance Settings; Overcurrent Settings - ABB REL 301 Instruction Leaflet

I.L. 40-386.4
1) If the calculated Zone-1 impedance is 0.5 ohms (secondary) or less the line percentage,
used for the calculation, should be 70-75%.
2) If the Source Impedance Ratio or SIR, (ratio of positive sequence source impedance to
positive sequence line impedance) is in the range of 3-5 the line percentage, used for the
calculation, should be no more than 75%.
3) Circuit fault impedance angles in the range of 80 degrees produce dc time consonant of
about one cycle. One cycle time constants result in maximum overreach error of about
16%. Hence the line percentage used should be no more than 70 - 75%. If the total fault
impedance angle is greater than 86 degrees, the dc time constant is greater than 2.3 cy-
cles, and the overreach error is reduced to 10 percent or less. The same is true if the fault
impedance angle is less than 75 degrees. If system fault impedance angles are known
to be either above 86 degrees or below 75 degrees, the line percentage, used for the
Zone-1 calculation, can be increased by 5 percent. (All angles are based on 60 Hz sys-
tems.)
4) If CCVT's, of the low-capacitance type, (e.g. 1960's vintage PCA-5 and PCA-8 designs)
are in use, the line percentage, used for the Zone-1 calculation, should be 70-75%. Se-
vere subsidence-transient related overreach has been noted in cases where low-capac-
itance CCVT's are used in "short line" applications. An alternative to reducing the Zone-
1 setting, is to introduce a Zone-1 time delay (T1) of one or two cycles and using the 80
percent Zone-1 reach calculation.
3.2.3

Zone-2 Distance Settings

Generally, Zone-2 reach is set for 100% of the protected line plus 50% of the shortest adjacent
line. If the shortest (or only) adjacent line primary impedance is 20 ohms, then the Zone-2 reach
setting would be:
"Zone-2 Ø" = 6 + (20 x 0.5) x 240/600 = "10 OHMS" and
"Zone-2 G" = 6 + (20 x 0.5) x 240/600 = "10 OHMS"
NOTE:
3.2.4

Zone-3 Distance Settings

Generally, Zone-3 reach is set for 100% of the protected line plus 100% of the longest adjacent
line emanating from the remote bus, while accounting for the infeed from the same remote bus.
If the longest (or only) adjacent line from the remote bus is 25 ohms primary, and the infeed ef-
fect may increase its impedance by 30%, then the Zone-3 reach setting should be:
"Zone-3 Ø" = 6 + (25 x 1.3) x 240/600 = "19 OHMS" and
"Zone-3 G" = 6 + (25 x 1.3) x 240/600 = "19 OHMS"
3.2.5

Overcurrent Settings

a. The low set phase overcurrent unit is used for supervising the load-loss-trip and close into
fault functions. It should be set higher than the line charging current and below the minimum
load current.
3-4
"Zone-2 Ø" and "Zone-2 G" can be set for different values if the application
requires.