Fault Current Limiter
1. Introduction
MCBs with short circuit level of 25 kA are not manufactured in India & abroad. At present fault current is cleared
by using rewirable fuses or miniature circuit breaker (MCB). In general, rewirable fuses are cheaper but slow.
On other hand, miniature circuit breaker is fast but has limited breaking capacity up to 10 kA. The existing rating
of MCB is 10 kA at rated voltage of 240/415 V. The MCBs are also used in LT switchgear; distribution
transformers, appliances and fault level can be up to 25 kA. If MCBs are not able to clear this fault current, there
is chance of fire. Therefore the objective of this invention is to develop a device that along with existing MCB can
clear fault up to 25 kA to prevent fire and personnel injuries. This will also increase the life of MCBs.
Fault current limiter (FCL) as the name suggest is used to limit the short-circuit current. When short-circuit current
of the system is greater than the rated breaking capacities of MCB, limiting of fault current up to rated breaking
capacities of MCB is possible with the use FCL in series. Hence, the let-through energy is limited by means of
FCL and there is no need of use of expensive and complicated moulded case circuit-breakers (MCCBs) having
higher breaking capacity.
Photograph of Fault current limiter
MCB in Series with Fault current limiter
2. Highlights of Technology
The switching action of FCL is based on PTC (Positive Temperature Coefficient) effect. This means that there
are no movable parts in the device and therefore no electrical arc and no wear of contact surface. Further,
automatic resetting occurs after limiting the fault. Hence reliability of the system increases. The new material
developed at ERDA has nonlinear characteristics and is operative at rated voltage of 240/415 V and 16 A. The
operating time is 3.5 milli second.
Potential applications of the FCL can be circuit breakers (MCB, ELCB), short circuit protective device (SCPP)
for motor, over current protection, load limiter, domestic appliances & rotating machines etc.
3. Benefits
When connected in series with MCB, it can enhance short-circuit breaking capacity of MCB at less than half the
cost of MCCB. For example, an assembly of MCB of rating 16A/10kA/240V/3P with FCL connected in series will
cost Rs. 2000/- against a MCCB of rating 16A/25kA/240V/3P at cost of Rs. 5000/-. The manufacturer can also
claim value addition in terms of light weight, higher safety and reliability. As the operating time is very short the
chance of catching fire is less. As there are no dynamical parts, and contacts, there are no issues related to
wear / erosion / breakages.
4. Expression of Interest:
Expression of Interest are invited from interested parties for technology transfer. Our contact details are as followDr. S. H. Chetwani,
Assistant Director
Electrical Research and Development Association
ERDA Road, Industrial Estate, Makarpura
Vadodara – 390010, Gujarat, India
Email: satish.chetwani@erda.org
Web: http://www.erda.org
Contact No.: 0265-3048044 (Direct)
Mobile: 9978940913