GE G60

GE Multilin G60 Generator Protection System 8-5
8 THEORY OF OPERATION 8.1 PHASE DISTANCE THROUGH 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 Ω ∠90° + 0.05779 Ω ∠85° = 0.1847 Ω ∠88.4° primary side or 2.569 Ω ∠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 Ω∠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 Ω∠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 Ω 87.5°∠ secondary== =
Z
T
at 13.8 kV()
10
100
----------
13.8 kV()
2
150 MVA
----------------------------
× 0.127Ω 90°∠==
Z
L
at 13.8 kV()30.11
13.8
315
-----------


2
× 0.05779Ω 85°∠==