Ground Directional Overcurrent; Description - GE D30 Instruction Manual

GROUND DIRECTIONAL OVERCURRENT

Consequently, the following signals are applied to the phase AB distance element:
This results in the following apparent impedance:
This 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 Ω ∠90° + 0.05779 Ω ∠85° = 0.1847 Ω ∠88.4° primary side or 2.569 Ω ∠88.4° on the secondary side.
This example illustrates how the relay maintains correct reach for fault behind power transformers. When installed at X,
the relay needs to 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 needs to be set to 2.569 Ω ∠88.4° to ensure exactly same coverage.
See the Application of Settings chapter for information on setting calculations.
9.3 Ground directional overcurrent

9.3.1 Description

Consider the negative-sequence directional overcurrent element. As shown, the negative-sequence voltage can be low
during internal fault conditions.
9
9-16
1
V = ----- -V V = 10.861 kV 59.9° primary or 94.45 V 59.9° secondary
–
AB BC
3
I = 3I = 58.860 kA ∠
–
B
V 94.45 kV 59.9°
Z = -- - = --------------------------------------- -
app
I 36.75 kA
( )
Z at 13.8 kV
T
Z ( at 13.8 kV ) =
L
Figure 9-6: Offset impedance augmentation
(a)
V_2
UR
(c)
V_2 >
I_2 * Z_2line
UR
∠ ∠
27.6° primary or 36.75 A ∠ 27.6° secondary
– –
∠
= 2.570 Ω 87.5° ∠
∠ °
27.6
–
2
( )
10 13.8 kV
------- - × ----------------------- - ∠
= = 0.127Ω 90°
100 150 MVA
2
13.8
 
---------
30.11 × = 0.05779Ω 85°
 
315
(b)
(d)
S_pol
I_2 x Z
-V_2
D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 9: THEORY OF OPERATION
secondary
∠
S_op
S_pol
I_2 x Z
V_2 -V_2
ECA
I_2
S_op
V_2
-V_2
ECA
I_2
837728A2.CDR
Eq. 9-1
Eq. 9-2
Eq. 9-3
Eq. 9-4