9. Conclusions

The pace of change in HV substations accelerated in the 90s and 95s:

• changing customer requirements in terms of personnel safety and reliability;

• the development of underground networks to replace overhead lines;

• the development of telecontrol ;

• the evolution of substation or switchgear control-command following the introduction of electronic and then digital relaying.

This development has resulted in :

• increased mechanical strength of cells;

• improved operating safety for internal arc equipment;

• the development of public distribution structure substations (particularly on underground networks),...