Subject of the invention relates to a monolith lighting arrester with high tensile strength and without inside gas room, especially for limiting overvoltages on out door electrical networks. The lighting arrester is comprising flexible insulating material surrounding ZnO varistors on waterproof way. Metal armatures are formed at the both ends of a bar made of glass-epoxy and being the support structure of the device on such a way that it ensures high tensile strength and because of this the overvoltage arrester suits to function as tightening insulator on electrical network.

Prior Art _ ^■

Metal-oxide lighting arresters are utilised on electrical networks since 1976. These lighting arresteres are used instead of the conventional devices with sparking gap of the high voltage networks. Varistors made of metal- oxide were developed in Japan in 1968. During wide-spreading process of the cable accessories and composite insulators it was thought that the light arresters can be provided by plastic housing instead of porcelain ones. This resulted easier handling, lower level of fragility and increased reliability.

In the case of this lighting arrester according to the invention the ZnO rings keep their electrical parameters (small leakage current, low level of oh ic loss and residual voltage, stability against current surge, high level of energy absorbing ability) for a long period and the light arrester should be change only in the case of direct (havarie) such as lighting stroke. The ZnO rings and the insulator preferably made of silicon elastomer embodying the rings provide permanent dielectric strenght, durability on out door circumstances and long-wearing of electric arc.

Stabile tensile strength respectively mechanical life period of the composite insulators are ensured by good proved glass-epoxy bar. Moisture cannot penetrate into the monolith lighting arrester casted aroung without any discrepancy under overpressure (as written in HU-PS No. 194.293) with preferably silicon elastomer and it is explosion proof in short circuit circumstances.

In a lab scenario modelling lighting stroke and destroying the silicon coating has got a hole due to the effect of the short circuit current with electric arc (electric arc is going to "extend") but the bar made of glass-epoxy remained completely intact. Bursting away of the broken ZnO rings' pieces - explosion - on the effect of the short circuit current with electric arc was prevented by the silicon coating. This destroying test proves very well that the glass-epoxy bar was able to hold the wire (because it remains intact) namely the supporting device was able to function further.

Monolith lighting arrester with high tensible strength according to the invention can be built in on networks instead of tightening insulator on the base of the quality described before i.e. dimensions of networks' lay outs in front of the transformers can be reduced - making the system more compact - and the lighting arrester can be installed nearer to the transformer being protected and separate console installation is not needed. It results from the facts mentioned before that using the solution according to the invention more economic installations with lighting arrester can be set up comparing them to the traditional solution because of not using consoles and tightening insulators leaving them out from the compact new solution and from the point of view of electric protection it is more safe.

More solutions are known for solving tasks described above. That type of solution is known from the desciption HU T 63013, where near on both ends of tablets made of varistor material at least two pieces of pressing elements made of

insulating material are fixed. These rigid plastic lathes are not able to endure the tensile stress prescribed for the tightening insulators. The above structure can be employed for bending on a very limited way so it can not be used as supporting insulator as well. For the installation of this type of lighting arresters a separate console is necessary which is expensive and it does not suit to the requirements of the modern compactibility.

The invention referred, because it does not utilise pressing elements with springs and the varistor tablets are not under continuous pressure, does not have liable electrical contact.

The further disadvantage of the structure is that the pressing lathes attached on the both sides of the varistors do not ensure uniaxial position for the device and this fact reduces the sufficient contact of the varistors on different ambient temperatures.

Summary of the invention The aim of the invention is to develop a lighting arrester without inner gas room which a high tensile insulating bar as core on each ends of the bar armatures made of metal can be attached and this device should be able to resist tensile load and the ZnO varistors located around the insulating bar should embedded - without cavities - in a flexible plastic material, which adheres to the ZnO varistors to insulating bar and to the metal armatures and it endures electric arc and the out door employment.

The object set up has been achieved with the lighting have been shaped in ring form and the ZnO varistors have been attached on an electric insulating bar and between the ZnO varistors metal discs ensuring good electric contact have been installed then at one end of the device a pressing spring is fixed. Metal armatures have been pressed on each of the insulating bar that the device arranged on this way has been put into a heated casting form in which using vacuum and over pressure liquid casting mass has been

- 4 - pressed which casting mass filled the cavities without any voids. The mass has been let to crosslink. The result was a flexible rubber like form.

The monolith lighting arrester with high tensile strength and without inside gas room according to this invention is suitable mainly for limiting over voltage appearing on out door electric networks. This lighting arrester consists of flexible insulating material surrounding the ZnO varistors on waterproof way, where the ZnO varistors are formed on ring shape they are attached on an electric insulating form in stake form. Metal discs providing good electric conduct are between "the ZnO varistors and armatures made of metal are fixed at the ends of the electric insulating bar. The ZnO varistors are pushed to each other by at least one piece of spring with permanent force.

Brief description of the invention

Fig. 1 shows the cross-section of the lighting arrester made according to the invention.

Surge arrester with high tensile strength according to the Figure 1 has at leas one armature 1 made of metal and the metal armature 1 has sealing surfaces attached to an electric insulating bar 2 made of one piece and ring-shape ZnO varistors 3 are attached on the insulating bar 2 so that metal discs 4 are attached between the ZnO varistors 3 ensuring good electric contact between the ZnO varistors 3 and the metal discs 4. The metal discs 4 and ZnO varistors 3 are pressed together by a spring 5, and there is matching layer 7 on the nappe surfaces of the ZnO varistors 3 and electrical insulating bar 2 and insulating bar 2, ZnO varistors 3, metal discs 4 and spring 5 are embedded in a water-proof electric insulating casting mass 6.

The advantage of this lighting arrester according to the invention is that it can be used as double function element on electric networks name as lighting arrester and tightening insulator as well, and it functions on such a way

that the insulating bar 2 employed on tension and the ZnO varistors 3 are casted around with a plastic able to stretch which plastic follows the thermal expansion of the electric insulating bar 2. A further advantage is that the lighting arrester according to the invention is without inside gas room it is so called monolith embodiment. In the case of direct lighting stroke (havary) the ring form ZnO varistors 3 wreck and brake because of the impact of electric arc on such a way that they do not destroy the insulating bar 2 inside and it is endures the tensile force further, and the flexible embedding material 6 does not allow to split the parts of the ZnO varistors 3 so it is semi explosion safe and it is not dangerous for its surrounding. A further advantage is that there is such matching (stricking) layer 7 on the nappe surface of the ZnO varistors 3 and metal armatures 1 and electrical insulating bar 2 which merges with chemical binding the embedding casting mass with components mentioned above. Resulting from this moisture penetration is hindered completely on the extreme ambient temperature scale as between -50 and +150 Celsius.

A further advantage is that there are no cavities micro wrecks in embedding casting mass which cross linked in warm casting form vacuumed and over pressurised and because of this there is no generated partial discharging and inside ionisation. The lighting arrester made on this way is very liable in function and its life period is 25 years at least.