Lightning arrester device

Abstract

 A lightning arrester device comprises a spark gap device (3) connected in parallel to a part of serial connection of non-linear resistors (1,2) whereby a limiting voltage characteristic as level of protection can be reduced to impart long life of the lightning arrester.

Description

BACKGROUND OF THE INVENTION:

[0001] The present invention relates to a lightning arrester device for power transmission system which is used for protecting a power transmission line, especially a lightning arrester device utilizing non-linear resistors.

[0002] It has been proposed to provide a lightning arrester for power transmission system which has no serial gap and which is a. non- dynamic current type one utilizing excellent non-linear resistive characteristic of a lightning arrester element prepared by sintering a composition comprising a main component of zinc oxide at 1200 to 1300°C in United States Patent No. 3, 806, 765.

[0003] Such lightning arrester has no serial gap and the lightning arrester element is formed only by the non-linear resistor whereby a response to lightning voltage application can be performed without any discharge delay. On the contrary, the system voltage ( AC or DC system voltage)is continuously applied to the non-linear resistor.
When a level of protection of the lightning arrester (limiting voltage characteristic)is reduced, a current passing in the normal state is increased to shorten the life of the lightning arrester. Therefore, the level of protection could disadvantageously not be reduced below a specific value.

SUMMARY OF THE INVENTION:

[0004] It is an object of the present invention to overcome the above-mentioned disadvantage.

[0005] It is another object of the present invention to provide a lightning arrester device which has a level of protection lower than the minimum level of protection attained by the conventional lightning arrester, even though the structure is simple.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0006] 

Figure 1 is an equivalent circuit diagram of the lightning arrester device of the present invention;

Figure 2 is a schematic view of the structure of the lightning arrester device of the present invention;

Figure 3 is a limiting voltage-current characteristic diagram for illustrating the operation of the lightning arrester of the present invention;

Figure 4 is a sectional view of one embodiment of a spark gap device used in the present invention ; and

Figure 5 is a partially sectional view of one embodiment of an insulator including lightning arrester which supports a power transmission cable according to the present invention.

[0007] In the drawings.the same references designate indentical or corresponding parts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

[0008] Figure 1 shows an equivalent circuit diagram of the lightning arrester device of the present invention and Figure 2 shows a schematic view of the structure thereof. As shown in the drawings, the lightning arrester device of the present invention comprises a serial connection of a first non-linear resistor (1) and a second non-linear resistor (2) which are respectively prepared by sintering a composition of a main component of zinc oxide at high temperature and which have excellent non-linear resistive characteristics and a spark gap device (3) connected in parallel to the second non-linear resistor (2). The first non-linear resistor (1) has a structure of piled up disc elements and the second non-linear resistor (2) has a cyrindrical structure as shown in Figure 4. The spark gap device (3) is formed by cup shaped metal plates which are disposed inside of the cylindrical non-linear resistor (2). That is, the flanges of the metal plates of the . discharge gap device (3) is held by the non-linear resistor (2).

[0009] The operation of the lightning arrester device of the present invention will be illustrated referring to the limiting voltage current characteristic diagram.

[0010] In the embodiment of Figure 1, the limiting voltage-current characteristic curves in the case of no connection of the spark gap device (3) are given by Figure 3 (A), (B), wherein the lightning voltage (corresponding to level of protection) to nominal spark current i₂ is given by v_3' On the contrary, in the device of the present invention, when the terminal voltage of the second non-linear resistor (2) reaches to a predetermined value, the spark is formed in the spark gap of the spark gap device (3) to form a short-circuit whereby the level of protection can be reduced to v₂ in Figure 3.

[0011] In Figure 3, the characteristic curves (C), (D) show characteristics of the non-linear resistor (1).

[0012] The spark gap device (3) is set to create a spark when the current i_l in the region of v₂≧v₁ is passed whereby the limiting voltage characteristic of the embodiment of Figure 1 is given as the full lines (A), (D) in Figure 3, to give the level of protection to v₂.

[0013] The spark in the spark gap device (3) is stopped by diminishing the lightning voltage which releases the spark gap device (3).

[0014] In accordance with the structure of the embodiment of the present invention, the limiting voltage characteristic of Figure 3(A) is given in the condition applying the normal voltage to ground v₀ to the lightning arrester whereby the above-mentioned low level of protection v₂ can be given without increasing the current passing in the normal state. The spark gap device is disposed inside of the cyrindrical non-linear resistor whereby an additional space for the spark gap device is not required advantageously.

[0015] As shown in Figure 5, the long trunk insulator (6) is formed in a hollow shape and the lightning arrester of the disc type first non-linear resistor (11) and the cyrindrical second non-linear resistor (12) having a same outer diameter are held in the hollow insulator whereby the lightning arrester device which can be used as supporting insulator for power transmission line can be obtained.

[0016] , In said structure, a diameter of the hollow part of the long trunk insulator (6) is preferably minimized from the economical viewpoint.

[0017] In the lightning arrester device of the present invention, the spark gap device is disposed inside the second non-linear resistor whereby the diameter of the hollow part of the insulator can be minimized.

[0018] In the embodiment of Figure 5, the reference numeral (7) designates a flange ; (8) designates a metal cover which is disposed at each end of the insulator (6) to form each terminal which is electrically connected to either of the non-linear resistor (11) or (12) ; (9) designates the O-ring for air-tightening ; (10) designates a cement for bonding the insulator (6) to the flange (7) in one body.

[0019] In accordance with the embodiment of the present invention, the lightning arrester device has a simple structure and imparts low level of protection without shortening the life of the lighning arrester.

[0020] When the level of protection is the same, the number of non-linear resistors to the normal voltage can be increased whereby the duty of each non-linear resistor of the lightning arrester device in the normal operation can be reduced to prolong the life of the lightning arrester.

[0021] In the structure, the spark gap device is disposed in the non-linear resistor, whereby a size of a container (usually an insulator) can be small when the lightning arrester elements are held in the container. The advantages of the present invention are remarkable in practical use,

Claims

1) A lightning arrester device with a serial connection of a first non-linear resistor and a second non-linear resistor characterized by a spark gap device (3) connected in parallel to at least one (2;12) of said non-linear resistors (1,2; 11,12).

2) A lightning arrestor device according to claim 1, characterized in that the non-linear resistor (1,2;11,12) is made of a sintered product comprising a main component of zinc oxide sintered at high temperature.

3) A lightning arrester device according to one of claims 1 or 2, characterized in that the second non-linear resistor (2;12) is in a cylindrical form and said spark gap device (3) is disposed inside the cylindrical non-linear resistor (2).

4) A lightning arrester device according to one of claims 1 to 3, characterized in that the first non-linear resistor (1;11) has a disc form and the second non-linear resistor (2;12) has a cylindrical form with the same outer diameter.

5) A lightning arrester device according to one of claims 1 to 4, characterized in that the first and second non-linear resistors (1,2;11,12) and said spark gap device (3) are held in an insulator (6).

6) A lightning arrester device according to claim 5, characterized in that each one terminal (8) connected to the non-linear resistor (1,2;11,12) is disposed at each end of said insulator (6).

Drawing