GE MiCOM P143 Agile User Manual

below shows earth fault current levels, below which they self-extinguish on these types of system. Statistics
demonstrate that around 80% of ear
th faults in Petersen Coil earthed systems self-extinguish. This, in part,
explains their popularity.
V00756
0
20
40
60
80
100
120
140
11kV 22kV 33kV 65kV 110kV
Earth fault extinction current limits
as per DIN VDE 0228 Part 2
Capacitive fault current—isolated neutral
Residual fault current—compensated neutral
Figure 52: Current level (amps) at which transient faults are self-extinguishing
The following figure depicts a simple netw
ork earthed through a Petersen Coil reactance. It can be shown that if
the reactor is correctly tuned, theoretically no earth fault current will flow.
V00631
jX
L
AN
L
V
jX
AB
C
V
jX

ac
C
V
jX

0
AN
f B C
L
AN
B C
L
V
I I I
jX
V
if I I
jX
   
  
Source
Petersen
Coil
Current vectors for A phase fault
If
-IC
A
BC
N
-I
B
I
L
V
AB
V
AC
-I
B
-IC
(=I
L
)
(=-I
B
) (=-I
C
)
-jX
C
-jX
C
-jX
C
Figure 53: Earth fault in Petersen Coil earthed system
Consider a radial distribution system earthed using a P
etersen Coil with a phase to earth fault on phase C, shown
in the figure below:
P14x Chapter 6 - Current Protection Functions
P14xEd1-TM-EN-1 125

GE MiCOM P143 Agile Specifications

General

Brand	GE
Model	MiCOM P143 Agile
Category	Control Unit
Language	English