Out-Of-Step Block (Os Block) Blinder Settings (Os Inner And Os Outer) - ABB REL 301 Instruction Leaflet

NOTE:
Assume that the line charging current is negligible for this line section and the minimum
load current is 2.0 Amps secondary, then the low set phase overcurrent unit setting should
be:
"Low IØ" = "1 Amps"
b. The medium set phase overcurrent unit is used for supervising the out of step blocking
function and all phase distance tripping functions. Care in selecting the medium set phase
overcurrent setting ("IM") must be exercised to prevent limiting the Zone-3 distance reach.
Traditionally, "IM" is set higher than load current whenever possible.
In general, the criteria for setting medium set phase overcurrent is 1.13 X Maximum load cur-
rent. Assume maximum load current is 4.0 amps secondary then:
"IM" = 4.0 Amps X 1.13 = "4.5 Amps" (approximately)
The setting should be reviewed to assure it does not limit the reach of zone-3.
c. The low-set ground overcurrent unit is used for supervising the reverse directional overcur-
rent ground unit (RDOG). It should be set as sensitive as possible. A setting of 0.5 amperes
is recommended:
"3I0s" = "0.5 Amps"
d. The medium set ground overcurrent unit is used for supervising all ground distance units,
the forward directional overcurrent ground unit (FDOG). Generally, it is recommended to
be set 2 times the 3I0s setting.
"3I0m" = 2 x "3I0s" = "1.0 Amps"
e. The directional high set overcurrent phase and ground units, "Inst. Ø" and "Inst. G" are
used for direct tripping functions. The general setting criterion for the instantaneous direct
trip unit is:
The unit should be set higher than 1.15 times the maximum fault on the remote bus, where
the factor of 1.15 is to allow for the transient overreach. For this example, assume that the
maximum load is not higher than the maximum forward end zone fault current, and the
maximum phase and ground fault currents on the remote bus are 20 and 24 amperes, re-
spectively, then the settings of the high-set phase (ITP) and the high-set ground (ITG)
should be:
"Inst. Ø" = 20 x 1.15 = "23 Amps"
"Inst. G" = 24 x 1.15 = "27.6 Amps"
3.2.6 Out-of-Step Block ("OS Block") Blinder Settings ("OS Inner" and "OS Outer")
The requirements for setting the blinder units are:
• Inner blinder must be set to accommodate maximum fault resistance for internal 3-phase
fault
It should be set above the maximum tapped load current if applicable.
I.L. 40-386.4
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