The subject of the invention is a gas insulated electrical switchgear placed in the enclosure and provided with at least one bushing for transferring electric energy through the enclosure of the switchgear.

From patent EP2494567 there is known a medium voltage apparatus closed in the enclosure and having a device for cooling the medium voltage apparatus. The device for cooling is using heat pipes, partially consisted in a casing of the apparatus. The heat pipe is filled with a working fluid. The part embedded into casing has an evaporator being in contact with current conducting part of the device connected by sleeve with condensation device placed outside the device. The sleeve is made of electrically insulating and thermally well conductive material. The disadvantage of this solution is the need of using insulating sleeve which must provide electrical separation between current path of medium voltage apparatus and the casing. In addition this arrangement require to provide a space for placing there a separate auxiliary cooling system, thus the size of the medium voltage apparatus need to be extended.

From patent US7253379 there is known a high voltage circuit breaker with cooling system in the form of a heat pipe. The heat pipe is a device having a sealed chamber for working fluid circulation. The working fluid circulates in liquid and gaseous phase. The circulation allows effective heat transfer between evaporator, where heat is absorbed by evaporation process, and condenser, where heat is released during condensation. The working fluid used in the heat pipe must have suitable dielectric strength because it circulates between evaporator placed on a conductive part of the circuit breaker being on high electrical potential and the condenser attached to grounded housing.

The essence of the present invention having a cooling device with a phase - change heat transfer fluid is that the switchgear is equipped with at least one bushing with a conductor for powering the switchgear and in the same time a cooling device which is integrated in the conductor (5) of the bushing (4) that forms a heat pipe. The heat pipe is filled with a working fluid. One end of the heat pipe forms an electrical bottom terminal connected with a conductive part of the switchgear whereas the other end of the heat pipe forms an electrical top terminal placed outside the enclosure of the switchgear. The heat pipe has a vaporizing part situated in the proximity of the bottom terminal and a condensing part situated in the proximity of the top terminal.

Preferably an upper part of the conductor of the busing is connected with a heat sink device.

Preferably a bottom part of the conductor of the busing together with the bottom terminal are free of an insulation.

Preferably the inner side of the cylinder of the conductor of the bushing is covered with a wick.

Preferably the wick has a form of a well-developed surface structure made on the inner side of the cylinder of the conductor of the busing.

Alternatively the wick has a form of a separate layer deposed on the inner side of the cylinder of the conductor of the busing.

The advantage of the present invention is that the cooling device is integrated within existing and irreplaceable part of the switchgear, i.e. the conductor of the busing, what does not require any additional electrical insulation. Moreover, the cooling device is embedded in a current path of the switchgear what causes that the heat is transferred directly out of place where it is generated by Joule's heating. Such arrangement allows for design of a compact electrical switchgear without any additional volume for placing there a separate cooling device.

The present invention is presented in an exemplary embodiment were:

• Fig. 1 shows the switchgear placed in the enclosure and connected with the bushing in a schematic view,
• Fig. 2 shows the bushing from fig.1 in a cross-section,
• Fig. 3 shows the bottom part of the bushing from fig.2 in a cross-section,
• Fig. 4 shows the upper part of the busing from fig.2.

A switchgear 1 is placed entirely in an enclosure 2 filled with a gaseous medium 3. Conductive part of the switchgear is connected with a bushing 4 for transferring electric energy delivered through the enclosure 2. The gaseous medium 3 could be air or another gas for example SF6 or any other gas which provides sufficient voltage withstand ability. The busing 4 is partially placed inside the enclosure and partially outside the enclosure.

The busing 4 has a conductor 5 made of copper or aluminum, in the form of a metal cylinder closed on both ends. The conductor is surrounded by an insulator 6 made of thermoplastic or thermosetting material which provides sufficient thickness for electrical insulation in relation to the rating voltage of the switchgear. The insulator 6 extends radially along the axis of the conductor 5 but not covering the both ends of the conductor 5. The insulator 6 is attached to a flange 7 made of steel or aluminum for mounting the bushing in an opening made in a wall of the enclosure 2, what is not presented in the drawing. Inside the conductor 5 there is a working fluid 8 in liquid and gaseous state in thermodynamic equilibrium. The conductor 5 with the working fluid 8 form a device commonly known as a heat pipe. The working fluid 8 must be delivered in amount assured a space for condensation in a section provided for heat dissipation and in amount sufficient to prevent full evaporation of the working fluid during maximum operating temperatures provided for the switchgear. Typical material applicable for working fluid are water, methanol or acetone. To enhance evaporation and condensation, the inner side of the cylinder 5 is covered with a wick 9. The wick 9 may be realized by preparing a special surface structure of inner side of the cylinder of the conductor 5, e.g. by grooving of the surface for receive well-developed surface structure, or by deposition a separate layer of material with fabric or mesh-like structure characterized by high thermal conductivity. The upper end of the bushing protruding from the enclosure 2 is equipped with a heat sink device 10 for better heat dissipation from the upper end of the conductor 5. The heat sink is made of material with high thermal conductivity. The ends of the conductor 5 form a bottom terminal 10 and a top terminal 12. The both terminals 10 and 12 must be free of insulation to provide good electrical connection and heat transfer. The switchgear 1 device is connected with electric line by top terminal 12, what is not presented in the picture.

During the work of the switchgear 1 Joule's heat generated by conductive part of the switchgear 1 is transferred by the bottom terminal 11 and heats the fluid 8 placed in the bottom part of the conductor 8. A new thermodynamic equilibrium is reached, where working fluid is boiling in bottom part of the conductor what is presented in Fig.3 by the arrows. It is important that the bottom part of the conductor 8 is free of any insulation protection what is needed for electricity conduction and heat transfer from conductive part of the switchgear 1 to heat pipe. For phase change process and working fluid transport enhancements wick 8 is used. When the evaporated fluid 8 reaches the top part of the conductor 5 the gaseous phase of working fluid 8 starts to condensate at wick 9 and inner wall of conductor. The wick 9 supports liquid phase transport as it was indicated in the drawing 4 by dotted arrows. Heat is transferred via conductor 5 to the heat sink 10, which enhances heat dissipation. The presented conductor 5 of the bushing 4 plays role of the heat pipe placed inside the busing.