Suppressing circulating currents in conductive structures in buildings

Abstract

The invention relates to a method for designing a lightning protection system for the exterior lightning protection of buildings and systems and to an insulated lightning arrester device related thereto. The lightning arrester of the lightning protection system is at least partly designed as an insulated electric conductor with a conductive layer or casing on the insulation, and conductive structures can be found in the respective building or the respective system, wherein the structures are potentially exposed to inductions which occur in the event of a lightning current to be arrested, and correspondingly the conductive layer on the insulated conductor together with the respective conductive structure forms a secondary loop.

Claims

1. A method for designing lightning protection systems for exterior lightning protection of buildings and installations, wherein an insulated lightning arresting line of a lightning protection system of the lightning protection systems is at least partly designed as an insulated electrical conductor with a conductive layer or casing of the insulated lightning arresting line, and conductive structures are located in a respective building or a respective installation, wherein the conductive structures are potentially exposed to an induction occurring in an event of a lightning current to be arrested, and correspondingly the conductive layer on the insulated lightning arresting line together with the respective conductive structure forms a secondary loop, including the following steps: analyzing a spatial position of the conductive structures in the building or the respective installation to be protected and determination of potential secondary loops; determining critical distances of the insulated lightning arresting line, and estimating an induction effect in the secondary loop from standard lightning surge current variables for a range of the critical distances which cannot be varied by increasing a separation distance, while considering a total length of the insulated lightning arresting line and a total displacement current resulting therefrom; comparing an evaluated potential maximum circulating current caused by induction in the secondary loop to an acceptable threshold value; modifying the insulated lightning arresting line if an excess of a threshold value is to be expected, by specifically increasing at least in longitudinal sections, a resistance value of the conductive layer or casing applied to the insulation of the insulated lightning arresting line, wherein an upper limit of the resistance increase is predefined by a floating discharge operating field strength in a respective section that had been modified in its resistance value; characterized in that the conductive layer of the insulated lightning arresting line is of high impedance over its entire operating length, however, a value of 10 kOhm/m is not exceeded; and characterized in that the increased resistance value is rated such that the current i2 in the respective secondary loop is 0.1 to 1% of the current i1 flowing in the primary loop, i.e. in the event of lightning current, through the arresting device.

2. The method according to claim 1, characterized in that the conductive layer or casing of the insulated arresting line is interrupted at least in longitudinal sections by a high-voltage resistant resistance segment that is free from floating discharges.

3. The method according to claim 1, characterized in that the conductive layer or casing of the insulated arresting line has at one or more longitudinal sections embedded, high-voltage resistant resistance areas that are free from floating discharges.

4. An insulated lightning current arresting device for the exterior lightning protection of buildings, objects and/or installations designed according to claim 1.

Description

(1) The invention will be explained below in more detail on the basis of an exemplary embodiment and with reference to Figures.

(2) Shown are in:

(3) FIG. 1 a principle representation of the induction effect in a secondary loop of a conductive structure in the building to be protected, and a usual low-impedance sheathing of an insulated arresting line according to the state of the art; and

(4) FIG. 2 the effect of a limitation according to the invention of the induced current in the secondary loop by using a high-voltage resistant resistor R rated according to the invention that is free from floating discharges.

(5) The circulating current i2 induced into the secondary loop is determined by the influencing variables amplitude and temporal progress of the lightning current to be arrested, the geometry of the secondary loop, and the resistance of the areas or segments of the conductive sheathing that had been modified according to the invention.

(6) The risk of a floating flashover on the surface of insulated arresting lines is likewise defined by the amplitude and the temporal progress of the lightning current to be arrested and the resistance of the segments to be dimensioned, but also by external influences along the arresting line, in particular also by conductive components situated in the proximity.

(7) Since the amplitude, the temporal progress of the lightning current, the geometry of the secondary loop, but also the external influences along an arresting line cannot be influenced or only to a certain extent, and insulated arresting lines per se should be universally applicable, the design and rating of resistance values is taken as a basis according to the invention for solving the assigned task, which resistance values apply with respect to the insulated arresting line at least in longitudinal sections in the area of the external conductive sheathing.

(8) An exemplary rating of the resistor surface or the formation of the corresponding longitudinal section will be explained below.

(9) It is known from a multitude of examinations and measurements that in a lightning current relevant voltage change velocity of du/dt=3 MV/μs on an insulated arresting line with a capacitance coating of C=100 pF/m per meter of running length, a capacitive displacement current of about 300 S becomes effective.

(10) When the entire length of the insulated arresting line is assumed to be 10 m, for example, and with an assumed linearly decreasing voltage distribution along the internal conductor of the insulated arresting line, an entire displacement current of 1500 A will be the result.

(11) If a floating discharge field strength of, for example, E.sub.GE=20 kV/cm is assumed, the resistance of the insulated arresting line in the relevant section or over the entire length will amount to about 1.33 kOhm/m as the maximum value which should not be exceeded if possible.

(12) In such an exemplary design, a circulating current in the secondary loop having a peak value of about 180 A and a pulse duration of 250 ns is the result in case of an assumed lightning current of lightning protection class I (negative following flash at 200 kA/μs and a coupling inductance of 1.2 pH/m underlying the standard).

(13) By means of the representation according to FIG. 1, an exemplary section of a lightning protection system for the exterior lightning protection is shown, wherein a lightning current arresting device is provided, which in case of a lightning strike discharges the lightning current i1 via an electrical conductor 1 to an earth electrode 2.

(14) Depending on the embodiment of the correspondingly equipped lightning protection system, the primary loop has an inductance L.sub.1.

(15) The employed insulated lightning protection arresting device has a conductive layer or casing 4 on the insulation 3.

(16) This conductive layer together with a conductive structure 5 in the building to be protected (not shown) form a secondary loop. This secondary loop has the inductance L.sub.2. Depending on the spatial allocation, a magnetic coupling M is the result.

(17) Without the measures according to the invention, the current i2 induced into the secondary loop may be between 30 and 50% or more of the current i1, with the consequence of negative effects upon the conductive structure itself or electronic or electrotechnical components situated on or in the proximity of this structure.

(18) A limitation of the current i2 induced into the secondary loop is performed with reference to a solution as symbolically represented in FIG. 2.

(19) In this respect, a targeted increase of the resistance value R of the conductive layer 4 applied to the insulation of the arresting line realized at least in longitudinal sections is performed.

(20) The upper limit of the resistance increase is predefined by the floating discharge operating field strength in the respective section modified in its resistance value.

(21) In the design according to the invention of the corresponding lightning protection arresting device, the circulating current i2 in the secondary loop amounts to about 0.1 to 1% of the current i1.

(22) The current i2 approximately results from di1/dt.