AN579 APPLICATION NOTE

6/10

Figure 10. Series and parallel protection

The secondary protection level is generally achieved with two types of devices:

– The series protection ensures protection against the proximity of or the crossing with AC power lines.

– The parallel protection operates to suppress the overvoltages due to the lightning effects.

Series devices: Series devices operate by opening the circuit or by an increment of the resistance.

Figure 11. Fuse protection

The fuse is a classical case of protection by opening the circuit. Figure 11 shows an exchange protected

by fuses and Figure 12 represents an example of the limit curve of the fusing action.

MODULE

TO BE

PROTECTED

1

2

1: Series protection.

2: Parallel protection.

LINE

EXCHANGE

FUSE

FUSE