Siemens 7SG164 Ohmega 400 Series Manual page 116

APPENDIX A
A.1 Fault Loop Compensation For Earth Faults
The relay is set in terms of positive sequence impedance. To calculate the actual fault loop impedance follow the
steps below. Start by recording the relay settings;
Line Angle
EF Comp Z0/Z1 Ratio
EF Comp Z0 Angle
Calculated
Compensation Factor,
Then calculate voltage, current and actual impedance using the formulae:
V = IZ (1 + K
1
Where Z1 is the positive sequence impedance (i.e. the relay setting)
Zone 1
Phase Effective
Impedance
A
B
C
Zone 2
Phase Effective
Impedance
A
B
C
Zone 3 (Fwd)
Phase Effective
Impedance
A
B
C
Zone 3 (Rev)
Phase Effective
Impedance
A
B
C
©2010 Siemens Protection Devices Limited
=
=
=
Earth Fault
K =
N
)
N
Total Loop
Impedance
Total Loop
Impedance
Total Loop
Impedance
Total Loop
Impedance
7SG16 Ohmega 402 60 Commissioning
⎛ ⎞
Z
⎜ ⎜ ⎟ ⎟
− 1
1
0
=
3
⎝ ⎠
Z
1
Current Phase
Injected Angle
Current Phase
Injected Angle
Current Phase
Injected Angle
Current Phase
Injected Angle
Voltage Phase
Injected Angle
Voltage Phase
Injected Angle
Voltage Phase
Injected Angle
Voltage Phase
Injected Angle
Chapter 9 Page 18 of 19