Medium voltage electric cells in metal case, for indoor use, covered, with simple bar system, air insulation, up to 24kV and 4000A Medium voltage electric cells in metal case, for indoor use, covered, with simple bar system and air insulation are electric equipment modular groups for alternating current used in medium voltage networks, which currently represent the optimal solution for distributing primary and secondary electric energy. This kind of medium voltage electric cells are widely used in the energy system, both for electric power production and distribution, connection and supply points, and for secondary distribution for MT/JT medium voltage substations, as well as for industrial networks or large individual users. Types: According to their location in the power system, the cells may be classified as follows: substation cells, used for the medium voltage primary distribution transforming substation cells, used for the medium voltage primary distribution, especially for the medium voltage side of the transforming substations MV/LV. According to their operation function, the cells may be classified as follows: line cell (input/output) motor cells (with circuit breaker, with contactor) special destination cells: tie, measurement etc. According to the equipment type: fixed equipment withdrawable equipment specially built equipment (for instance, fixed equipment on withdrawable module). According to the commutation environment within the circuit-breaker: vacuum commutation SF6 commutation

Constructive features

A. The medium voltage cells consist of a metal enclosure, made of steel plate panels, fixed with special rivets, fitting parts or by spot welding, which house the medium voltage equipment according to the operation requirements, including the removable trolley and the low voltage metering, control, protection and signaling devices. The enclosure has a slotted cover and a double wall (behind the cell) for exhausting the gases resulting from a free electric arc and for guiding them upwards. The electric cells are free-arcing proof, according to the tests performed in authorized laboratories.

B. The support and passage insulators are made of cast epoxy resin mixture.

C. The cells are extensible, designed as to enable an easy insertion of new cells in an electric point. The cells have an extensible general bar bridge having the distribution bars usually made of copper, as well as a general earthing bar made by cooper, which ensures the continuity of the grounding circuit along the entire point and which may be connected to the earth socket of the electric point.

D. The cells have screw terminals for medium voltage cables mounting.

E. The cables in the cable channels enter the cells through cuttings in the basis of the cells. These cuttings are fitted with pre-cut aluminum covers and insulating plates which may be cut according to the size of the connection cables.

F. The connection to the medium voltage network may also be carried out by bars, usually made of copper, both through inferior and superior connections, usually by sealed bar bridge.

G. The secondary circuits are separated from the medium voltage side by metal screens or, on small areas, by insulating tubes. All cells are provided with facility of passing the secondary circuit cables to the secondary cables compartment. The connections between secondary circuits of the cells of an electric point are connected through the cables tunnel located above the secondary circuits compartment.

H. The cell compartments are fitted with a resistance connected through a thermostat for condensation elimination. Inside the cells, lamps are fitted within the secondary circuits compartment.

I. The secondary circuits connecting the fixed side (cell) and the trolley are of type plug socket with several flexible contacts and conductors, which allow the shifting of the trolley from the “work" position to the "test" position.

J. The medium voltage electric cells are mounted in closed rooms, on a horizontal metallic base rigidly fixed on the floor.

Usage conditions

according to SR EN 62271-200:2003 and SR EN 60694:2003, with the following mentions:

• Climate area: Climate group WDr/CT (moderate  climate: hot dry/temperate/cold), according to SR HD 478.21S1
• Ambient temperature range: Min. -5°C, Max. +40°C
• 24 hours average ambient temperature: Max. +35°C
• Air relative humidity: Max. 80% at 20°C
• Ambient environment: Must be dust free, free of corrosive or inflammable gases, no vapors or salts above limits currently allowed by regulations for indoors electric installations / The aggressiveness coefficient of the atmosphere is normal
• Maximum altitude: 1000m / For attitudes higher than 1000 m, the supplier should be consulted

The above conditions are considered normal for the transport, storage and installation period as well, taking into account that the minimum temperature of the environment can fall as low as -25°C.