system. The neutral point resistor gives a 10 A ground-fault current during a zero
resistance ground-fault. This means that the resistance is
GUID-4ECDF824-B17E-436D-A668-ACA06BB375F7 V2 EN (Equation 18)
The total zero sequence impedance of the 22 kV system is:
Z
0
= 3R
N
// j3X
N
// — jX
C
Ω / phase
As the Petersen coil is tuned the zero sequence impedance is:
Z
0
= 3R
N
Ω / phase
The residual voltage during a resistive ground-fault in the 22 kV system is:
0
0 0
1
3 3
1 1
Phase
o
f f
phase
V V
V or
R R
V
Z Z
= =
× ×
+ +
GUID-AD49C138-F37B-4690-9E37-BA2BAD678A17-ANSI V1 EN (Equation 19)
In our case the requirement is that ground-faults with a resistance up to 5 000 Ω shall be
detected. This gives:
0
1
0 20
3 5000
1
3 1270
phase
V
.
V
= =
×
+
×
GUID-42D376ED-052F-4E9B-B4D9-8D679127BC0C-ANSI V1 EN (Equation 20)
Step 1 and step 2 is given the same voltage setting but step 2 shall have longer time delay.
The residual ground-fault protection shall have a definite time delay. The time setting is
set longer than the time delay of the ground-fault protection of the outgoing feeders having
maximum 2 s delay. The time delay for step 1 is set to 3 s and the time delay for step 2 is
set to 4 s.
1. Set GlobalBaseSel to 2
The (LV) winding data should be related to Global base 2.
2. Set Characterist1 to Definite time
3. Set Pickup1 to 20 % of VBase
4. Set t1 to 3.0 s
5. Set Pickup2 to 20 % of VBase
6. Set t2 to 4.0 s
Section 3 1MRK 511 286-UUS A
REC650 setting examples
56
Application manual
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