DEVELOPMENT OF FAULT CURRENT LIMITER
By Aradhana Ray
1.0 INTRODUCTION
Fault
current limiter (FCL) as the name suggest is used to limit the
short-circuit current. When FCL is used in series with Miniature circuit
breaker (MCB) with lower short circuit breaking capacities during fault
condition, let-through energy(I2t) through MCB is less than the designed
value. Due to low let-through energy, increased personal safety and system
reliability can be achieved. When short-circuit current of the system is
greater than the rated breaking capacities of MCB, limiting of fault
current upto rated breaking capacities of MCB is possible with the use FCL
in series as shown in Fig.1. Hence, rapid and efficient way in which the
let-through energy is limited by means of FCL, there is no need of use of
expensive and complicated moulded case circuit-breakers (MCCBs) having
higher breaking capacity.
2.0
EXPERIMENTS
When
FCL is used for limiting let-through energy for fault current of 25 kA
with the miniature circuit breaker having maximum breaking capacities of
10 kA, MCB has cleared the fault and the results are mentioned below;
Comparison
test on MCB with and without Fault Current Limiter
Fault
Current 10 kArms, 240 V, 50 Hz, MCB only
|
Sr.No.
|
Operation
|
Cut-off
Current
(kA)
|
I2t
(let through energy) A2S
x 103
|
Operating
time
in msecs.
|
Remarks
|
|
1
|
‘O’
|
3.640
|
21.72
|
4.505
|
Only
MCB
|
|
2
|
‘CO’
|
3.272
|
17.28
|
5.065
|
Only
MCB
|
Fault
current 25 kArms, 240 V, 50 Hz MCB with fault current limiter
|
Sr.
No.
|
Operation
|
Cut-off
Current
(kA)
|
I2t
(let through energy)
A2S x 103
|
Operating
time in
msecs.
|
Voltage
drop across limiter.
(Vpk)
|
Remarks
|
|
1
|
`O'
|
3.328
|
9.041
|
2.372
|
110.4
|
MCB
with FCL
|
|
2
|
`CO'
|
3.784
|
13.75
|
3.757
|
133.6
|
MCB
with FCL
|
2)
CONCLUSION
From
the above test result, it is very obvious that cut-off current and let
through energy during short circuit test on MCB at 10 kA is almost equal
to that during short circuit test on MCB with FCL at 25
kA. Therefore, it can be proved that MCBs having 10 kA breaking capacities
with fault current limiter in series is equal to MCBs or MCCBs having 25
kA breaking capacities.
3)
OTHER FEATURES
1.
No movable parts
2.
Light in weight & can be used with lower rating MCB (i.e. old
protective service).
3.
Reduce risk of fires & damage of connected equipment.
4.
New concepts
5.
Increase life of the protective device.
