Introduction to the History of Selective Protection

Author: Walter Schossig, Germany

The Fusible Link

The distribution grids proposed by Edison and his company to supply electric lighting systems used fusible links. In 1880 the fusible links used strips of lead ("Edison Lead Switch").

Another solution discussed a "lever switch whose lever had a reduced diameter which fused at a certain level of current".

In the early days of electric power systems the protection requirement was simply to interrupt the flow of fault current. However selectivity emerged as a growing requirement as electric power systems became more complex with interconnection of transmission lines and the parallel operation of generators.

In 1910 the municipal utility in Hannover was one of the first recorded cases to introduce a color code for fuse identification. The utility had specified the use of fuses on every feeder to achieve selectivity on their system. The utility specified the size of fuses required for all lines and, in an effort to make the specifications more memorable, the authorities in Hannover used a fuse identification color code based on the color of stamps issued by the German postal authority.

 

Figure 1: Color of the German stamps and the fuse identification color code


Fuse

Stamp

Rated Current [A]

Color

Value in pfennigs

Color

6

green

5

green

10

red

10

red

20

blue

20

blue

25

yellow

25

yellow+black

 

In 1904 Kortler proposed the idea of time delayed self reclosing fuses. This technology is widely used today in medium and high voltage grids and is referred to as automatic reclosing or autoreclosing.

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