Page 323 - Practical Power System and Protective Relays Commissioning

Protection Relays Settings Chapter | 19 317

I F
V S 5 5 R loop max
CT
40; 000
5 3:86 5 128:66 V
1200

V S 5 130 V
Choose relay R V 5 130 V, I RV 5 35 mA
Range: 25 175 V
Knee point of CT is as follows:
V K min 5 2V S 5 2 3 130 5 260 V

Choose CT with V k 5 300 V
Use a current relay with burden 3500 Ω, I 5 30 mA.
As before in the M 1 calculation:
R sh 5 99.23 Ω V metrosil 5 1053 V
R series Resistor (RS) 5 833 Ω C 5 450, β 5 0.25
I metrosil 5 30A for 2 seconds
Then check the zone relay CH calculation:
R lead 1 5 2 3 R 7 1 R CT2
0:33 3 2 1 2:9 5 3:56 Ω

R lead 2 5 2 3 R 8 1 R CT4
2 3 0:31 1 2:9 5 3:52 Ω

R lead 3 5 2 3 R 9 1 R CT8
5 2 3 0:33 1 2:9 5 3:56 Ω

R lead 4 5 2 3 R 10 1 R CT10
5 2 3 0:39 1 2:9 5 3:68
R lead max 5 R lead 4 5 3.68

I F
5
V S R L max
CT
40; 000
5 3:68
1200
5 122:66
Set V S 5 125 V
Choose the relay range: 25 175 V
V set 5 125 V I RV 5 35 mA
The knee point voltage of CT should be as follows:

V K min 5 2 3 V S 5 2 3 125 5 250 V
Choose V K 5 300 V of CT using a current relay with burden 5 3500 Ω