UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
10A
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
GROUND
FAULT
PATH
HIGH RESISTANCE
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
9
If the MV system is high resistance neutral
grounded (Figure 5) the application of the Ar-
cLimiter solution needs to change. These types of
systems are typically applied in older industrial
plants, feeding a process. A single line to ground
fault does not cause major damage and the MV
switchgear breakers usually do not have ground
fault protection. Indications of a ground fault are
usually detected via installed voltmeters. The oper-
ating process continues as a plant benefit.
The UFES closes all three phases to ground simulta-
neously. At this point, the LV AF is essentially over.
Depending upon UFES closing time and phase se-
quence, phase A and B CLF melt in 1 ms (MV voltage
system recovery starts) with full CLF interruption
by 1.5-2 ms (SCC dependent). When phases A and B
CLF clear, the entire phase C current (now very lim-
ited) appears as a zero sequence current.
The only path for fault current is through the phase
C CLF to UFES phase C PSE to transformer’s neu-
tral, but is now very limited by the source neutral
return path’s resistance (Figure 6).
—
High resistance/grounded MV
systems
If the MV system is high resistance neutral grounded, the application of
the ArcLimiter solution needs to change.
—
05 MV system is
high resistance
neutral grounded
—
06 Path for fault current
is through the phase C
CLF to UFES phase C PSE
to transformer’s neutral,
but is now very limited
by the source neutral
return path’s resistance
—
05
—
06
