Calculation For Impedance Earthed Systems; Figure 220: Residual Voltage For A Solidly Earthed System - GE MiCOM P40 Technical Manual

P446SV

Figure 220: Residual voltage for a solidly earthed system

As can be seen from the above diagram, the residual voltage measured on a solidly earthed system is solely
dependent on the ratio of source impedance behind the protection to the line impedance in front of the protection,
up to the point of fault. For a remote fault far away, the Z
small residual voltage. Therefore, the protection only operates for faults up to a certain distance along the system.
The maximum distance depends on the device setting.
5.3.2

CALCULATION FOR IMPEDANCE EARTHED SYSTEMS

Consider a Phase-A to Earth fault on a simple radial system.
P446SV-TM-EN-1
S
E
Z
V
A
V
V
B
C
V
A
V
B
V
C
V =
RES
2Z
S1
E00800
IED
Z
S
L
V
A
V V
V
C C
B
V
RES
V
RES
V
V
A
B
V
C
Z
S0
+ Z + 2Z + Z
S0 L1 L0
/Z : ratio will be small, resulting in a correspondingly
S L
Chapter 14 - Voltage Protection Functions
F
V
B
V
B
V
C
X 3 E
397