GE Multilin D60 Line Distance Protection System 8-15
8 THEORY OF OPERATION 8.2 PHASE DISTANCE APPLIED TO POWER TRANSFORMERS
8
If applied at location H, the relay sees the following input signals:
The relay is set as follows:
XFMR VOL CONNECTION = “Dy11”
XFMR CUR CONNECTION = “Dy11”
Consequently, the following signals are applied to the phase AB distance element:
(EQ 8.1)
(EQ 8.2)
This results in the following apparent impedance:
(EQ 8.3)
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:
(EQ 8.4)
Thus, 0.127 90° + 0.05779 85° = 0.1847 88.4° primary side or 2.569 88.4° on the secondary side.
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.
INPUT PRIMARY SECONDARY
VA 7.584 kV –5.59° 69.95 V –5.59°
VB 6.269 kV –120.1° 54.52 V –120.1°
VC 7.751 kV 125.5° 65.84 V 125.5°
IA 16.976 kA –27.6° 10.61 A –27.6°
IB 33.952 kA 152.4° 21.22 A 152.4°
IC 16.976 kA –27.6° 10.61 A –27.6°
V
1
3
-------
V
AB
V
BC
– 10.861 kV 59.9 primary or 94.45 V 59.9 secondary==
I 3I
B
– 58.860 kA 27.6 primary or 36.75 A 27.6 secondary––==
Z
app
V
I
----
94.45 kV 59.9
36.75 kA 27.6–
----------------------------------------------
2.570 87.5 secondary== =
Z
T
at 13.8 kV
10
100
----------
13.8 kV
2
150 MVA
----------------------------
0.127 90==
Z
L
at 13.8 kV30.11
13.8
315
-----------
2
0.05779 85==
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