ABB REL 301, Instruction Manual

Page: 73 / 132

I.L. 40-386.3
(10/94) 3-5
3.2.4 Zone2 Distance Settings
Generally, Zone2 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 Zone2 reach setting would be:
Zone2 Ø = 6 + (20 x 0.5) x 240/600 = 10 and
Zone2 G = 10
NOTE:Zone2 Ø and Zone2 G can be set for different values if the application
is required.
3.2.5 Zone3 Distance Settings
Generally, Zone3 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 effect may increase its impedance by 30%, then the Zone3 reach setting should
be:
Zone3 Ø = 6 + (25 x 1.3) x 240/600 = 19 and
Zone3 G = 19
NOTE: Zone3 Ø and Zone3 G can be set for different values if the applica-
tion is required.
3.2.6 Overcurrent Settings
a. The low set phase overcurrent unit is used for supervising the OS Block, the load-loss-trip
(LL Trip) and CIF Trip functions. It should be set higher than the line charging current and
below the minimum load current.
NOTE: It should be set above the maximum tapped load current if applica-
ble.
Assume that the line charging current is negligible for this line section, and the
minimum load current is 2.0 A secondary, then the low set phase overcurrent unit
setting should be:
Low IØ = 1
b. 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