Calculating Settings For Step 2 - ABB REC650 Applications Manual

Section 3
REC650 setting examples
3.1.6.3
54
The calculations show that the largest residual current from the transformer = 1.2
kA.
To assure selectivity the setting must fulfil:
I ≥ 1.2 · k · 3I
high,set
which gives about 1 500 A ,where k is the transient overreach (due to the fault current
DC-component) of the overcurrent function. For the four step residual overcurrent
function; k = 1.05.
2. Set t1 to 0.4 s
Characterist1: ANSI Def.Time
As the protection should be set for a time delay of 0.4 s the selectivity to the line
protections should be assured. Therefore ground-faults should be calculated where
the fault point on the lines is at zone 1 reach (about 85 % out on the line).

Calculating settings for step 2

1. Set Pickup2 to 400% of IBase, corresponding to 956 A
To assure that step 2 detects all ground-faults on the outgoing lines ground-faults
calculations are made where single phase-faults and phase-to-phase-to ground-
faults are applied to the adjacent busbars.
ANSI11000130 V1 EN
Figure 12: Fault calculation for sufficient reach of the 145 kV residual
overcurrent protection
The minimum residual current to detect works out as 3I
2. Set t2 to 0.8 s
Characteristic2: ANSI Def.Time
The delay of Pickup2 should be set longer than the distance protection zone 2
(normally 0,4 s). 0.8 s is proposed.
0 max
51N_67N
145 kV
3
1MRK 511 286-UUS A
REC650
1
Ph-Ph
1
Y
Y
3
Y
1
ANSI11000130-1-en.vsd
= 1.0 kA.
0AB,min
Application manual
22 kV