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9 THEORY OF OPERATION
INPUT
PRIMARY
100.4 kV –7.32°
VA
97.23 kV –53.4°
VB
181.8 kV –150.0°
VC
1.288 kA –27.6°
IA
1.288 kA 152.4°
IB
IC
0
If installed at the location X, the relay would use the following input signals for its phase AB distance element:
= 77.402 kV 57.5° primary or 29.49 V 57.5° secondary
V = V
AB
= 2.576 kA –27.6° primary or 42.93 A –27.6° secondary
I = I
– I
A
B
And consequently it would see an apparent impedance of:
= V / I = 30.05 85° primary or 0.687 85° secondary
Z
app
If applied at location H, the relay sees the following input signals:
INPUT
PRIMARY
7.584 kV –5.59°
VA
6.269 kV –120.1°
VB
7.751 kV 125.5°
VC
16.976 kA –27.6°
IA
33.952 kA 152.4°
IB
16.976 kA –27.6°
IC
The relay is set as follows:
= "Dy11"
XFMR VOL CONNECTION
= "Dy11"
XFMR CUR CONNECTION
Consequently, the following signals are applied to the phase AB distance element:
1
------ - V
V
AB
3
I
3I
This results in the following apparent impedance:
Z
app
The above value is a correct measure of the distance from the VT location to the fault. For relay location 2, this certainly
includes the positive-sequence impedance of the transformer:
Thus, 0.127 90° + 0.05779 85° = 0.1847
The above example illustrates how the relay maintains correct reach for fault behind power transformers. When installed at
X, the relay shall be set to 0.687 85° secondary in order to reach to the fault shown in the figure. When installed at H,
the relay shall be set to 2.569 88.4° to ensure exactly same coverage.
See Chapter 9: Application of Settings for more information on setting calculations.
GE Multilin
9.4 PHASE DISTANCE APPLIED TO POWER TRANSFORMERS
SECONDARY
38.25 V –7.32°
37.04 V –53.4°
69.26 V –150.0°
21.47 A –27.6°
21.47 A 152.4°
0
SECONDARY
69.95 V –5.59°
54.52 V –120.1°
65.84 V 125.5°
10.61 A –27.6°
21.22 A 152.4°
10.61 A –27.6°
V
10.861 kV 59.9 primary or 94.45 V 59.9 secondary
BC
58.860 kA
27.6 primary or 36.75 A
B
V
94.45 kV 59.9
--- -
--------------------------------------------- -
I
36.75 kA
27.6
10
13.8 kV
Z
at 13.8 kV
--------- -
--------------------------- -
T
100
150 MVA
13.8
---------- -
Z
at 13.8 kV
30.11
L
315
88.4° primary side or 2.569 88.4° on the secondary side.
L90 Line Current Differential System
27.6 secondary
2.570 87.5
secondary
2
0.127 90
2
0.05779 85
(EQ 9.37)
(EQ 9.38)
(EQ 9.39)
(EQ 9.40)
9
9-33
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