Logo   ABOUT EXPULSION FUSE LINKS  
      The fuses have been produced for about a hundred years and today they are being used all around the world. They play a vital role in the protection of equipment and electrical networks, assuring that the failures that happen inevitably, don't cause too much damage and that the continuity of the supply of electrical power to the customers is maintained at a high level. Besides, the cost of a fuse is incomparably lower than the cost of the equipment it protects (e.g. a transformer), so the use of fuses considerably reduces the final cost of energy.

   Foto1
Foto5     There are various types of fuse links, depending on the characteristics of their design and nominal and fault values they handle:

 
  • type K fuses are called fast element fuse links. They have velocity ratio* which is 6 for 6 amperes systems and 8 for the 200 amperes ones;
  • type T fuses are fuse links with a slow element. Their velocity ratio, for the same systems, is 10 and 13, respectively;
  • type H fuses are called extra-fast element fuse links. Their velocity ratio is 4 and 6.
  • DUAL type fuses are extra-slow, their velocity ratio is 13 and 20 (for 0.4 and 21 amperes, respectively).
*velocity ratio is the relation between the melting current at 0.1 seconds and at 300 seconds. (For fuses whose capacity exceeds 100 amperes, the value of 600 seconds is used.)

    The K and T type fuses have been preferred by the electric sector during more than 20 yeas due to their mechanic and electric interchangeability. This longevity has been contrasted with the introduction of the DUAL SLOW-RAPID ® class fuse link. This kind of fuses results advantageous not only in the protection of the network but also in the maximum usage of the capacity of the distribution transformers. (To see the characteristics of the DUAL fuse link, click here)

     The K and T fuse links comply with the ANSIC 3742 standard, while DUAL and H types - with NEMA SG2 – 1986 standard.

Conventional fuse link versus Dual type fuse link

    The conclusions that can be drawn from the analysis of characteristics of transformers and conventional fuses** are surprising: 2 fuses are needed for a full protection of the system: one for the transformer and another for the system. The solution is a DUAL type fuse link, which is called this way because there are two kinds of protection in one element: against shortcuts and against overcharge, with the benefit of not wasting the transformer's capacity. The DUAL type fuse link has the best time-current characteristic of all the fuses developed until today. Thanks to its design, it allows the maximum usage of the overcharge capacity of a transformer and assures immediate removal of the circuit in case of the transformer's failure or sporadic damage. That's why it is recommended to use Dual type fuse links in order to obtain the best protection, avoid unnecessary interruptions of service and get the possibility to overcharge the transformer to its maximum capacity.

** this analysis, due to its rather large size, is not shown on these pages.
 
 

   Traditional fuse

Dual fuse
1 Terminal
2 Washer
3 Auxiliary tube arc extinc
4 Fuse wire
5 Filter wire
6 Ferrule
7 Extraflexible tinned copper cable
8 Insulator
9 Ceramic
10 Winding
11 Coupling


 
Because of limitation of space, the information included herein is very general. If you want to deepen it, if you are interested in broadening your knowledge of any particular subject or if you wish to know how to choose the best fuse link to protect your electric system, just contact us.