GE Multilin g60, Instruction Manual

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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 3 I
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
---------------------------- ×
0.127
Ω
90
° ∠
= =
Z
L
at 13.8 kV
( )
30.11
13.8
315
-----------
 
 
2
×
0.05779
Ω
85
° ∠
= =