CN1034200Y - Lightning current transmission device - Google Patents

Abstract

Around the insulating core 1, a first conductor grounded by the lightning current transmission device is arranged, which is composed of metal wires 2, and is distributed parallel to the overall axis 3. The annular insulating layer 4 is arranged around the metal wire 2 . A second conductor composed of metal wires 5 is arranged around this intermediate insulating layer 4 . The second conductive parts are also distributed parallel to the axis 3 and are connected together to form a shield. The outer insulating layer 6 surrounds the whole 5 . These conductors 2, 5 minimize their resistance and inductance, improving lateral flashover suppression. A suitably sized high voltage terminal accommodates the upper portion of the device to introduce lightning strikes into the electrically isolated system.

Description

Lightning current transmission device

It is well known that there is a serious danger in lightning current transmission devices, because when the lightning current transmission device is struck by lightning, a discharge occurs between the bare copper wire of the standardized grounding conductor and the nearby objects or people, the so-called high-energy lateral flash network.

Due to the increasing height of the protected building structures, it is impossible for lightning currents to be confined in exposed ground conductors without disaster: fire, electric shock to personnel, damage to electrical and electronic equipment, etc.

The present inventors have proposed a device for transmitting lightning to earthed equipment which alleviates the above-mentioned disadvantages (see US Patent No. 3919956 and corresponding patents in other countries).

For all conventional grounding down conductors that cannot be concentrated into a hermet-ic facility (which is only possible if the facility is a hermetic coaxial structure), and for the above-mentioned No. 1 The patents mentioned in paragraph 3, with the help of concepts related to high pressure technology, make it possible to accomplish the improvements described in the present invention through creative efforts.

Lateral flashovers occur along bare or generally insulated grounded down conductors when the voltage gradient is higher than the withstand value. The surface field strength of a bare round wire depends on its diameter and the surrounding environment. When a lightning current passes through the wire, the voltage that appears depends on the AC longitudinal resistance of the wire.

This resistance can be calculated by solving Maxwell's equations for a round wire using the Bessel function. A representative view of this phenomenon can be explained by the concept of penetration depth. In this way, the insight of the "actually used part" of the lead wire can be introduced. The spectral range of lightning current is 20 to 100 kHz. For copper round wires, the penetration depths are 0.48 and 0.21 mm, respectively. Therefore, the hollow round wire is superior to the solid round wire of the same cross section.

Example: For φ6mm bare copper wire Rca=2.1mΩ/m(20KHz) Rca=4.6mΩ/m(100KHz) For EF special cable Rca=0.9mΩ/m(20KHz) Rca=2.2mΩ/m(100KHz) The improvement factor is about Values above 2 are calculated using classical formulas taken from the following three references: (1) High Voltage Electric Field (H. Prinz, Oldenburg Press) (2) High Voltage Technology (Professor K. Baierger Textbook) (3) Eddy currents and shielding in communication technology (H. Carden, Ph.D., Springer Publishing House) These values have been checked by laboratory measurements on the actual structure of the present invention, and the results are as follows: (i) When When the insulation size in the middle is suitable, even if the central conductor passes through the lightning impulse current, no lateral flashover has ever occurred, and the structure itself is not found to be damaged.

(ii) When a lightning impulse current is passed, a glow discharge phenomenon of very low energy can be observed around the structure, but no damage. One hundred years ago, Tesla had observed those discharges when experimenting with high-frequency currents.

Since the value of the surge current in the lightning conductor depends on the peak value of the surge current and the discharge waveform, the inventors were able to benefit from the very comprehensive data on lightning current pulses recently presented by Anderson and Eriksson in order to study The working condition of the main body of the grounding device of the present invention and its characteristics are determined. The present invention enables a grounding device capable of withstanding various lightning currents.

A full study of all those parameters shows that the impedance, ie the resistance of the lightning conductor and the inductance of the metal shield, has a detrimental effect and should be reduced first. However, the shielded cable has an intermediate conductive portion which consists of a bundle of metal wires helically wound around an intermediate core made of insulating material. And its metal shielding is realized by using wire or metal tape helically wound on the insulating layer that wraps the inner conductive part.

As a result, even if the coils and shields that make up the inner conductive portion are connected, or overlap (in the case of metal strips instead of wires), current flows through the helix due to the inevitable oxide layer on the surface of these wires or metal strips. line rather than straight lines, thus increasing resistance and inductance.

The purpose of the present invention is to use wires or metal strips parallel to the center line of the cable, so that the impedance is significantly reduced, and the performance of the lightning conductor is improved.

The lightning current transmission device of the invention adds a metal shield to the grounding down-conductor, an insulating layer is arranged between the grounding wire and the metal shield to keep a certain distance therebetween, and the metal shield is also wrapped with the insulating layer and then grounded as a whole. The grounding downconductor of the lightning current transmission device includes a first conductive part of the lightning current, an insulating layer covering the first conductive part and a second conductive part completely covering the insulating layer, and the entire lower end is grounded; the grounding downconductor It is characterized in that: the above-mentioned two conductive parts are each made of a bundle of filamentary metal wires, and these filamentary metal wires are distributed along the direction parallel to the center line, and the center line is shared by the two conductive parts and the intermediate insulating layer. centerline.

The drawing shows an embodiment of such a lightning conductor. Figure 1 is a partial side view, peeled off layer by layer, showing its internal structure. FIG. 2 is a cross-sectional view at 2-2 of FIG. 1 . Figure 3 shows the high voltage terminals on the upper part of the lightning current transmission device.

In the structure of the wire of this lightning current transmission device, the insulating core of circular section is represented by 1, and a metal wire 2 is installed around it, and the wire 2 is arranged in the direction parallel to the center line 3; if the cable is straight, The centerline 3 is the axis of the entire cable. These wires 2 constitute the first ground part of the lightning current transmission device, starting from the top end (not shown) of the lightning current transmission device to the grounding device (not shown). Due to the skin effect of the high voltage current, the space of the insulating core 1 does not need to be filled with the wire 2 .

An insulating layer 4 wraps the conductor layer 2, and the thickness and quality of the insulating layer should be able to withstand the impact of the part 2 passing through the lightning current. The second bundle of metal wires 5 is also distributed parallel to the central axis 3 . All these wires 5 form the second conductive part, which completely surrounds the insulating layer and therefore also the first conductive part 2 . All these conductors 5 form an electrical shield to conductor 2, the lower end of which is grounded (not shown).

A protective layer 6 made of an insulating material of suitable size is arranged around the conductor layer 5 . The conductors 5 may be overlapping parallel strips of metal so that they form an ideal electrical conduit.

It is conceivable that the second conductive part 5 is indeed tubular, but this has serious disadvantages: it is difficult to roll this structure without causing damage, and it is also difficult to roll into a roll when storing and transporting the cable. Using a bellows construction will make it easy to roll, but since the current in this part will flow along the corrugated path in this case, the resistance will increase, and first the inductance will increase.

Regardless of the external conditions, the requirements for the electrical insulating properties of the entire length of the structure are defined. It requires the use of a concentric conductive shield, just like high-voltage cables. In this way, it is possible to place such lightning conductors close to metal tips or edges without any adverse effect on their withstand voltage values.

High-voltage insulation must be mechanically protected to avoid damage during transportation, installation, and use; a solid metal body and armor that is resistant to severe weather can fully play this role.

Finally, thanks to the protective shield, the state of the high voltage insulation can be checked at any time with two simple electrical tests.

From the above considerations, it is possible to realize a grounding down-conductor of a lightning current transmission device suitable for the requirements of the contemporary world, and its lateral breakdown risk rate is 45-90% lower than that of bare conductors. Laboratory tests and calculated values confirm this indicator.

Using an existing coaxial structure (i.e. not manufactured like a conventional coaxial cable nor used like it), the inventors have for the first time possible to examine its properties in the laboratory by mathematical methods and extensive experiments ; Lightning current transfer devices are only effective when the structure is not charged. To achieve this basic purpose, it is designed with a high voltage terminal by means of which the device is able to transmit all lightning impulses without energizing the structure. The use of air electrostatic charging (through end 3) automatically generates primary free electrons (through end 2) determined by the value of the lightning quantity to ensure lightning breakdown (at end 1).

Claims (3)

1. Lightning current transmission device, its grounding down-conductor comprises a first conductive part (2) of lightning current, an insulating layer (4) surrounding the first conductive part and a second conductive part (4) completely surrounding the insulating layer. 5), the lower end of the whole is grounded; it is characterized in that: the above-mentioned two conductive parts (2 and 5) are each made of a bundle of filamentary metal wires, and these filamentary metal wires are distributed along the direction parallel to the center line (3). , the line (3) is the central line shared by the two conductive parts (2 and 5) and the intermediate insulating layer (4). 2. The lightning current transmission device according to claim 1, characterized in that the second conductive part (5) of the grounding down conductor is composed of overlapping metal strips, which together form a metal cylinder. 3. The lightning current transmission device according to claim 1 or 2, characterized in that a high voltage terminal is provided on the upper part of the grounding down conductor.