Toshiba GRZ100 B Series, Instruction Manual, Page: 408 / 447

⎯
407
⎯
6 F 2 S 0 8 4 6
Therefore, load current IL is:
IL = (Source voltage)/(A s/s back imp Line imp B s/s impedance)
= (150kV/ 3 )/(0.94
×
75 + 16.8
×
(0.0197
2
+ 0.2747
2
) + 0.94
×
75)
= 594.7A
3.2 Minimum fault current
The minimum fault current Ifmin on a protected transmission line is the current of the phase to
earth fault on the nearest remote terminal.
To calculate Ifmin, zero sequence earth fault current (Io), positive sequence earth fault current
(I1) and negative earth fault current (I2) are calculated as follows:
I0 = I1 = I2 = (Source voltage)/{(Back impedance of A s/s)
+ (Transmission line zero sequence impedance)
+ (Transmission line positive sequence impedance)
×
2*}
= (150kV/ 3 )/{(0.94
×
75) + 16.8
×
(0.4970
2
+ 1.4387
2
)
+ 2
×
16.8
×
(0.0197
2
+ 0.2747
2
) }
= 822.28A
So,
Ifmin= I0 + I1+ I2 = 3
×
822.28 = 2.47kA
*Note:
Assuming that positive sequence impedance = negative sequence impedance.
B s/s
Line length: 16.8km
A s/s
M
Earth fault
GRZ100