Date Code 20010625
Setting the Relay
9-39
SEL----311L Instruction Manual
Parameter Primary
Secondary
Z1S = Z0S
10
Ω
∠
87
°
primary
1.20
Ω
∠
87
°
secondary
Source R impedances
Z1R = Z0R
35
Ω
∠
87
°
primary
4.20
Ω
∠
87
°
secondary
PTR (potential transformer ratio)
230 kV : 115 V = 2000 : 1
CTR (current transformer ratio)
1200 : 5 = 240 : 1
CT burden class at station S and R
C800
CT burden at station S and R
1.0
Ω
Phase rotation
ABC
87L Communications
Single Channel
Line charging current
16 A primary
Maximum forward load at station S,
including tapped load
1100 A
Maximum reverse load at station S
600 A
Maximum tapped load (firm)
200 A (79.7 MVA)
Maximum load imbalance
5%
Convert the impedances to secondary ohms as follows:
12
.
0
2000
/
240
PTR
CTR
k
=
=
=
Equation 9.1
Z
secondary
= k • Z
primary
Equation
9.2
For example:
Z
1L1 (secondary)
= Z
1L2 (secondary)
= k • Z
1L1 (primary)
= 0.12 • (5.93
Ω
∠84.7°)
= 0.71
Ω
∠84.7°
Perform a system fault study with the transformers at base load during the study. The load at
Station S is 104 A at -25.1 degrees. Total load on the tap is 144.4 A at -25.3 degrees.
Table 9.7: Primary Fault Study Data, as Seen by Terminal S
(Differential Current in Parentheses)
Fault
Location
Fault
Type
I
A
Amps
∠
∠
∠
∠
0
I
B
Amps
∠
∠
∠
∠
0
I
C
Amps
∠
∠
∠
∠
0
I
R
Amps
∠
∠
∠
∠
0
Zf Apparent
Impedance at
Station S
Amps
∠
∠
∠
∠
0
R ABC
6081.0
-85.6
(9874.6 -86.2)
6081.0 154.4
(9874.6 153.8)
6081.0 34.4
(9874.6 33.8)
0
(0)
11.8 84.5
AG
4654.9
-82.2
(8442.2 -84.4)
491.4 89.7
(131.2 -134.1)
659.1 83.1
(132.9 83.3)
3538.9 -78.3
(8397.3 -84.9)
11.8 84.3
BC 103.9 -25.1 5311.6 -175.9 5221.1 4.7
0
11.8
84.5
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