UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
51G
BONDING JUMPER
UFES: 3 PSEs
(CLOSED)
MV “E” RATED FUSES
MV BUS (3 PHASE)
OIL or DT
XFMR
LV EQUIPMENT
(3 PHASE)
MV SWITCH
(normally closed)
REA
BONDING
JUMPER
A
C
B
51G-2
51G-1
GROUND
FAULT
PATH
T EC H N I C A L A N D A P P L I C AT I O N G U I D E
7
If the MV system is not solidly grounded, but low
resistance neutral grounded (Figure 3) the applica-
tion of the ArcLimiter solution needs to change.
The UFES closes all three phases to ground, simul-
taneously, when triggered. At this point, the LV AF
is essentially over.
Depending upon UFES closing time and phase se-
quence, phase A and B fuses melt in 1 ms (MV sys-
tem voltage recovery starts) with full CLF interrup-
tion by 1.5-2 ms (SCC dependent). When phase A
and B CLF clear, the entire phase C current appears
as a zero sequence current on the test traces. There
is a large reduction in phase C fault current once
phases A and B CLF open.
The only path for fault current is through the phase
C fuse, to UFES phase C PSE, to the transformer’s
neutral, but is now limited by the source neutral re-
turn path’s resistance (Figure 4).
—
Low resistance/grounded MV
systems
If the MV system is not solidly grounded, but low resistance neutral
grounded, the application of the ArcLimiter solution needs to change.
—
03 MV system is not
solidly grounded,
but low resistance
neutral grounded
—
04 Path for fault current
is through the phase C
fuse, to UFES phase C
PSE, to the transformer’s
neutral, but is now lim-
ited by the source neutral
return path’s resistance
—
03
—
04
