Alstom SHPM 101 - 19.19 Checking minimum relay voltage for a fault at the Zone 1 reach point; a) Phase faults

SERVICE MANUAL R5888B
QUADRAMHO Chapter 1
Page 24 of 27
Compensation setting = K
N
x Z
Ph
= 0.492 /4.8° x 4.8 /70°
= 2.36
/74.8°
Z
N
= K4 +K5 + K6 /QN°
I
n
Select K4 = 2
K5 = 0.3
K6 = 0.06
θ
N
=75°
Actual Z
N
= 2.36 /75°
Course ground loop impedance = Z
Ph
+ Z
N
= 4.8 /70° + 2.36 /75°
= (1.64 + j4.5) + (0.61 + j2.28)
= (2.25 + j6.78) = 7.14
/71.6°
19.19 Checking minimum relay voltage for a fault at the Zone 1 reach point
a) Phase faults:
Maximum positive sequence impedance behind relay is a maximum JAN source
impedance plus one circuit only of JAN – FEB line.
= 24.9
/88° + 20 x 0.44 /69°
= (0.87 + j24.88) + (3.15 + j8.22)
= (4.02 + J33.1) = 33.3
/83.1°
Impedance to Zone 1 reach point = 8.74
/70° ohms secondary
= 20.96
/70° ohms primary
= (7.17 + j19.7) ohms primary
Total source to Zone reach point impedance
= (4.02 + j33.1) + (7.17 + j19.7)
= (11.19 +j52.8)
= 53.97
/78° ohms primary
For a phase fault voltage seen by relay
= 20.96
/70° x 110
53.97 /78°
Magnitude = 42.7V