4
A RCLI M ITE R
TM
A R C FL A SH M I T I G AT I O N S O LU T I O N FO R LV US I N G U FE S
Abbreviations used in this document
AF:
arc flash
AWG:
American Wire Gage
CLF:
current limiting fuse
FLA:
full load amperes
LV:
low voltage
MV:
medium voltage
PSE:
primary switching element
QRU:
quick release unit (of the UFES)
REA:
ABB’s dedicated arc flash detection relay
SCC:
short circuit capacity
SUS:
secondary unit sub, MV-LV
51G:
AC inverse time earth overcurrent relay
(residual method)
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This solution is appropriate for:
-Light and heavy industrial
-Commercial facilities
-Educational campuses
-Any facility applying primary
loop fed transformers with
fused MV switches (36 kV
limit), new or existing applica-
tions
-Facilities having MV to LV
transformers in the range of
750 KVA – 5000 KVA
To prove this solution concept, tests were per-
formed at a third-party test laboratory. During an
actual LV arc flash event (performed per IEEE
C37.20.7), the REA detected and responded to the
AF event, sending a closing signal to the UFES.
The REA is advertised to detect and close its out-
put trip contact within 2.5 milliseconds (ms). With
the current setting at 1.5x the CT primary rating
and the light detection adjustment at mid-range,
this third-party test proved the REA responded
within 1 ms.
This response placed negligible voltage on the
transformer primary, extinguishing the LV arc
flash quickly (approximately 4 ms). Test results in-
dicate the incident energy level peak was 0.5 cal/
cm2, which is well below the AF threshold of 1.2
cal/cm2, where PPE is required.
A note on the CLF application is in order. A fuse
will become current limiting when the magnitude
of amperes through it is large enough to fully in-
terrupt in ¼ cycle or less, i.e., the fault waveform’s
peak is never reached. In general, for each appli-
cation with an applied UFES and MV E rated fuse,
the applying engineer needs to obtain the SCC (in
amperes) available at the upstream MV BUS. The
MV E rated fuse will reach its current limiting
threshold (¼ cycle interruption) when the ratio of
SCC to fuse full load ampere rating is 25 times at
a minimum. If the ratio is less than 25, the fuse
will take many cycles to fully interrupt. With the
UFES closed, the MV BUS is now at zero volts,
negatively impacting plant operations.
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ArcLimiter
TM
Introduction
Many industries are facing internal or external deadlines to implement
arc flash (AF) mitigation solutions within their facilities. ABB now
offers ArcLimiter
TM
, an arc flash mitigation solution that is unique in
the industry. It solves the LV AF problem at the MV or LV system level.
Many industries have internal distribution system configurations as
shown in Figure 1. The REA and UFES are ABB product additions to
this typical configuration that comprise the ArcLimiter AF mitigation
solution.
