Modular indoor substations for high and extra-high voltages

In the 1980s, the growth in consumption and the policy of improving quality of service in the main industrialized countries led to a significant need for new substations to supply the medium-voltage (MV) network (20 kV in France) from the high-voltage (HV) network (63 kV or 90 kV). The implementation of this major program to supply even medium-sized conurbations was bound to give rise to problems of integration in an urban or suburban environment, where overhead technology for lines and substations would be difficult to accept.

This raised the question of industrial development of a new type of substation that could be easily integrated into any environment. Advantages such as reduced floor space, simplified maintenance, protection of equipment against pollution and aesthetic integration into the environment were expected, as well as economic benefits, particularly in comparison with existing solutions that already offered a number of solutions, such as metal-clad substations.

First introduced in France in 1962, the first 63 kV indoor substations used by several French city authorities and a few industrial customers were air-insulated and installed in a traditional concrete building. The switchgear used was oil-insulated, with the live parts elevated and protected by a simple wire mesh, while the bars or connections were sometimes insulated. Drawing on this experience and the know-how acquired in the field of medium-voltage switchgear, manufacturers have been able to achieve the levels of quality and safety required by the specifications for what are now known as modular indoor substations (MIS).