Sectionalization of Overhead Contact Systems

the division of contact systems into electrically insulated sections. The sectionalization of a contact system permits the disconnection of any section, without a power shutdown in other sections, when, for example, an emergency occurs or preventive maintenance is carried out. Sectionalizing switches or circuit breakers are generally used to connect or disconnect adjacent sections. A distinction is made between longitudinal and transverse sectionalization.

In longitudinal sectionalization, the overhead suspension is divided along an electrified railroad line by insulating transitions at the joints between adjacent sections. The ends of adjacent sections are suspended in parallel on several supports of the contact system so that an air gap, or section gap, of 400–550 mm is left between them. This arrangement ensures a smooth passage of the current collector of the locomotive through the insulating transition. During this passage, the electric insulation of the sections is violated for a short time. If such a violation cannot be permitted because of the operating conditions prevailing in the contact system, the insulating transition is provided with a neutral insert, which is a segment of the contact system that is electrically insulated from both sections. The length of the neutral insert must be greater than the distance between the first and last current collectors of the electric locomotive or train; a train that passes under a neutral insert must move solely by inertia. Individual sections may consist of the overhead suspension of railroad track spans, stations, and large structures. At large stations, individual sections may consist of the overhead suspension at, for example, necks and groups of tracks. The overhead suspension is sectionalized also at traction substations and at sectionalizing points, which are used to protect the contact system from short-circuit currents.

Transverse sectionalization involves overhead suspensions arranged in parallel—usually above switches at necks of railroad stations or above special-purpose tracks, such as loading and unloading tracks and servicing tracks. Such sectionalization is obtained by connecting section insulators to all conductors of the overhead suspension to eliminate interference with the free passage of the current collectors of the rolling stock.

At stations where sections of railroad lines that operate on alternating and direct current come together, the overhead suspension system is divided into sections supplied both with alternating and direct current.