Page 310 - Practical Power System and Protective Relays Commissioning

304 Practical Power System and Protective Relays Commissioning

where β 5 0.2 C 5 450
I 5 30 A
V metrosil 5 (30) 002 . 450 5 888 V
So, for CT with 1 A secondary use metrosil with
C 5 450, β 5 0.2
I metrosil will be 30 A for 2 seconds
V metrosil 5 888 V

19.5.3.2 Worked Example 2 (Fig. 19.5.10)

Autotransformer 500 MVA 500/220 kV
HV side CT 1 600/1 R CT1 5 1.5 Ω
LV side CT 2 1600/1 R CT2 5 2.5 Ω
Neutral CT 3 1000/1 R CT3 5 2.5 Ω
Relay stability limit 5 16 I n 5 I through fault
I through fault
V s 5 stability voltage 5 3 loop resistance
CT
500 3 10 3
V S1 HV side 5 16 3 p ffiffiffi ð R 1 1 R 2 1 R CT1 Þ
3 3 500
16 500 3 10 3
5 3 p ffiffiffi ð 2 1 2 1 1:5Þ
600 3 3 500
5 15:396 5:5Þ 5 84:678 V
ð

FIGURE 19.5.10 500/220 kV autotransformer 500 MVA protected by high-impedance differ-
ential protection.