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The above figure shows a three feeder system. There are dropdown boxes for the device option in each feeder. The available
protection devices from the inventory are one type L recloser and 4 different type T fuses. The fault currents at the
device locations and at the end of each three phase feeder are indicated in the diagram. The continuous load currents for the three feeders are
also shown above.
This example is about recloser-fuse coordination so we choose a recloser device in the source side (note: so far
only 1 type of recloser in the inventory, which is type a L recloser, with 140-ampere series coils, and 2 fast and delay operations).
Based on the recloser characteristic, it should suitable for the continuous load currents in line 1. The recloser that we choose
also has to be able to interrupt any fault between the substation to point A. The recloser has satisfied the three requirements for proper
recloser operations. The recloser has a 4000 amps interrupting rating at 14.4 kV, and it is sufficient to to interrupt 1650 amps at the
substation secondary side. The recloser also has a 140 ampere rating recloser coil, which is more then the 90 amps continuous line current.
Finally, a minimum trip value of 280 amps allows the recloser to detect the lowest fault current at the end of line 2.
Now, we can try to choose the other protection devices on the other feeders.
The fuse and relosers have to be coordinated so that, for any faults between point A and ends of line 1 and line 2, the circuit is first
interrupted by the recloser on its fast curve, after which, if it is a permanent fault, it should be cleared by the fuse protecting
line 1 or line 2. Now, we will not know whether there is a miscoordination or not until we run the simulation, so the device selection is based
on the continuous current that the fuse can carry.
So, in line 2, 30T fuse is choosen since the peak load current is less than 30 amperes. Similarly, 40T fuse is choosen for line 3 since the peak
load current is less than 40 amperes.
After that, we are ready to run the simulation. The result are shown in the figure below.
From the coordination curves we can see that there is no indication of miscoordination. From the matlab screen we can find out that the intersection of the 30T and
40T fuse with the recloser fast curve are 1551 amperes and 2063 amperes, which is higher than the 1190 amperes maximum fault indicated.
The coordination curves also shows that none of the fuses maximum clearing time curves intersect with the recloser delayed curve, which means
the coordination is also achieved for permanent fault. This result is confirmed by the analysis output box,
which says that all line are coordinated successfully.
If for some reason we chose a 20T fuse for line 2, the result is shown below.
From the coordination curves, it shows that the 20T fuse is to small since 1035 amperes at the intersection is not satisfactory for the
1190 amperes maximum fault current. The simulation also indicates there is a misscordination at line 2 and suggest a bigger fuse size.
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