GB2376139A

GB2376139A - Arcing Section capable of carrying lightning current

Info

Publication number: GB2376139A
Application number: GB0204105A
Authority: GB
Inventors: Jan Meppelink
Original assignee: Obo Bettermann GmbH and Co KG
Current assignee: Obo Bettermann GmbH and Co KG
Priority date: 2001-03-24
Filing date: 2002-02-21
Publication date: 2002-12-04
Anticipated expiration: 2022-02-21
Also published as: ES2192149B1; HK1049743A1; NL1019801C2; DE10114592A1; GB0204105D0; FR2822600B1; ES2192149A1; CN1377108A; NL1019801A1; CN1286232C; GB2376139B; HK1049743B; FR2822600A1

Abstract

In order to create an arcing section capable of carrying lightning current with several arcing sections connected in series, the arcing section consisting of n arcing part-sections (FS), whose arc drop voltage is brought to a level of n times the arc drop voltage of one arcing part-section by the series connection of the arcing part-sections (FS), and the arcing part-sections (FS), with the exception of the first arcing section (FS1) to operate in the event of a lightning strike, being wired with capacitances, so that the arcing part-sections (FS) break down successively, the second and every other arcing section (FS2 - FSN) being connected directly to a common reference potential via the capacitances, in such a way that it only fires in the event of an overvoltage due to lightning, it is proposed that the sizing of the control capacitors is carried out in accordance with the following formula:<BR> (n-1) x CE = k x CL x where n is the number of capacitors, CE each control <EMI ID=2.1 HE=12 WI=6 LX=1036 LY=1680 TI=UI> <PC>capacitor, k a safety factor 1, CL the capacitance of the conductor from the arcing<BR> section to the source of the overvoltage, <EMI ID=2.2 HE=5 WI=5 LX=1419 LY=1961 TI=UI> <PC>the peak value of the overvoltage and U<SB>s</SB> the protection level of the arcing section.

Description

2376 1 39

Arcing section capable of carrying lightning current The invention relates to an arcing section, capable of carrying lightning current, with several arcing sections connected in series, the arcing section consisting of n arcing part-sections, whose arc drop voltage is brought to a level of n times the arc drop voltage of one arcing part-

section by the series connection of the arcing part-

sections, and the arcing part-sections, with the exception of the first arcing section to operate in the event of a lightning strike, being wired with impedances, in particular capacitances, so that the arcing partsections break down successively, the second and every other arcing section being connected directly to a common reference potential, in particular earth potential, via the impedances, and impedances of equal size being used in each case.

Arcing sections of this kind are known from DE 197 42 302 A 1 and DE 197 55 082 A 1 for example.

It is known that an arcing section or a multiple arcing section can be used for transient potential equalization, the subsequent secondary grid current being extinguished at the same time. The operation of an arcing section of this type can be divided into four basic functions: 1. Firing of the arcing section when an overvoltage due to lightning occurs.

2. Diverting or carrying the lightning current between earth and conductor and ensuring a low voltage drop along the arc.

3. Carrying and extinguishing the secondary grid current.

4. Re-establishing the arcing section and withstanding the recurring voltage at the location of the arcing section.

The i Movement described in the following relates exclusively to the firing of the arcing section in the event of transient overvoltages and lightning overvoltages due to principal lightning strikes as well as to the firing of the arcing section, particularly in the case of overvoltages of this kind due to lightning which occur in the event of follow-up lightning strikes and which have an increased rate of rise compared with such principal lightning strikes.

With regard to the first part of the problem, it should be noted that with all previous technical solutions, the firing of the arcing section of the lightning current conductor takes place as a result of any transient overvoltage such as, for example, the burst pulses produced when switching off inductive loads, the rupturing of fuses and switching overvoltages in the widest sense when the magnitude of the overvoltage exceeds the firing voltage of the arcing section of the conductor. This means that a lightning current conductor will operate each time such an overvoltage occurs.

Depending upon the point in time at which firing takes place, this can result in a secondary grid current, which, depending on the design of the lightning current conductor, is interrupted by this conductor or by an upstream fuse.

However, according to the task set for it, the lightning current conductor should really only fire in the event of an overvoltage due to lightning. It would be advantageous if firing due to other overvoltages could be prevented, as a result of which the lightning current conductor would be less stressed and the grid would be freed from unnecessary voltage disturbances and the rupturing of fuses would be avoided.

It is therefore a task of the invention to create an arcing section in such a way that it fires only in the event of an overvoltage due to lightning.

With regard to the second part of the problem, it should be noted that it is a known fact that, at 90t, the negative cloud-earth lightning discharge represents the major part of all lightning strikes. In turn, with negative cloud-earth lightning discharges, negative follow-up strikes occur in about 50 of cases, the rate of rise of which is significantly greater than that of the first principal lightning strike. However, the arcing sections are tested with regard to their operation with the lightning overvoltage of the first principal lightning strike. The operating behaviour with negative follow-up strikes is not tested according to the current standards. As the arcing sections are, nevertheless, subjected to this loading, the operating behaviour of the arcing section must be optimised for this loading.

The objective is thus to extend the protection level afforded by the arcing section, which has previously only been defined for a lightning impulse voltage of 1.2/SOps, to the loading imposed by negative follow-up strikes while at the same time achieving the same level of protection.

According to the invention, this is achieved by sizing the control capacitors in accordance with the following formula: (n-1) x CE = k x CL x us where n is the number of capacitors, CE the individual control capacitors, k a safety factor 1, CL the circuit capacitance of the conductor from the arcing section to the source of the overvoltage, u the peak value of the

- 4 overvoltage and Us the protection level of the arcing section. As a result of this, the operating behaviour of the multiple arcing section is set up such that transient overvoltages due to switching operations do not trigger the multiple arcing section but overvoltages due to lightning will always trigger the multiple arcing section if the signal energy of the overvoltage is sufficiently large to fire all the arcing part- sections. If the signal energy of an overvoltage due to lightning, for example caused by a remote lightning strike, is not sufficient to fire the entire multiple arcing section, the voltage will nevertheless remain limited to a value less than the protection level.

Re-firing of the lightning current conductor after the secondary grid current has been extinguished is made more difficult as the transient recurring voltage is absorbed by the control capacitors.

A further objective of the invention is to extend the protection level afforded by the arcing section, -which has previously only been defined for a lightning impulse voltage of 1.2/50gs, to the loading imposed by negative follow-up strikes while at the same time achieving the same level of protection. Due to the gas discharge processes, all arcing sections exhibit a more or less pronounced sluggish behaviour, the reason for which is the statistical discharge delay of the first electrons in the gas. The discharge delay is thus a disadvantage for all lightning current conductors with only one arcing section. This effect also occurs with a multiple

- 5 arcing section. The last arcing part-section to fire in a multiple arcing section thus determines the voltage at which it operates. Every arcing section displays this behaviour in the impulse characteristic, which defines the relationship between the breakdown voltage and the breakdown time.

Therefore, as the slope of the impulse voltage increases, the operating voltage of the arcing section also increases.

In the case of extremely steep overvoltages, this can lead to the protection level given by the operating behaviour for a lightning impulse voltage of 1.2/50ps being exceeded.

Exceeding the level in this way is possible with such overvoltages, which result from negative follow-up strikes.

To modify the arcing section for such conditions, it is proposed that the arcing part-sections with the exception of the first arcing part-section are provided with varistors, which are connected in parallel with each of the arcing part-sections, the varistors being sized according to the following relationship: (n-1) Ur + UAIC < US, where n is the number of arcing sections, Ur the residual voltage of the varistor, UAK the voltage on the first arcing section FS i, given by the anode and cathode drop, and Us the protection level of the multiple arcing section.

By means of this circuit using varistors, the protection level is advantageously maintained safely even when the rate of rise of the impulse voltage is very high.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure l a first circuit arrangement according to the invention together with an equivalent circuit diagram; Figure 2 a modified embodiment of the arcing section together with an equivalent circuit diagram.

Figure 1 shows the arrangement of a multiple arcing section.

The overvoltage u(t) is applied to the entire multiple arcing section and initially fires only the first arcing part-section FS1 with its selfcapacitance C12. After the first arcing part-section has fired, the voltage UFS2 ( t) = U(t) 2E U(t) since C23 < < C2E C23 + C2E

appears on the arcing part-section FS2.

As a result of this, the arcing part-section FS2 will also fire Correspondingly, all the other arcing part-sections will fire in succession.

However, when each of the arcing part-sections fires, an amount of the signal energy of the pulse voltage u(t) is removed in order to charge up the control capacitors C1E ONE. If the signal energy is limited, as in all transient overvoltages caused by switching operations, the signal energy will be fully absorbed if the size of the control capacitors ClE C(N-l)E is sufficiently large so that the nth arcing part-section is no longer able to fire, as the voltage remaining on the nth arcing part section is less than its firing voltage.

The control capacitors can be sized in accordance with the following criteria.

- l Linear control. All CEs are of the same size. The size of the control capacitors can be determined by the consideration below as follows: On the arcing-section side is the conductor capacitance CL, which would be charged up to a voltage U as a result of a transient overvoltage The charge on this section of conductor is then [lacuna]. In the presence of a multiple arcing section, this charge is now consumed by the control capacitors when the multiple arcing section fires. If the last arcing part-section is not to fire, the charge may only be distributed across n1 arcing part-sections. After the charge has been distributed, a voltage of only the same magnitude as the protection level should still be present on the multiple arcing section. A charge Q = (n-1) *CE*US is then present on the control capacitors. By equating the charges Q = Qua and taking a safety factor into account, the size of the control capacitance can be determined.

(n-1) * CE = k * CL * us u = peak value of the overvoltage US = protection level of the arcing section k = safety factor 1 where CL is the capacitance of the conductor from the arcing section to the source of the overvoltage.

In the event of a lightning strike, a practically infinitely large-signal energy is produced, which in every case will cause all arcing partsections to operate.

Thus, the operating behaviour of the multiple arcing section is advantageously set up such that

Transient overvoltages due to switching operations do not trigger the multiple arcing section.

Overvoltages due to lightning cause a triggering in every case provided that the signal energy of the overvoltage is sufficiently high to fire all the arcing part-sections. If the signal energy of an overvoltage due to lightning (caused for example by a remote lightning strike) is not sufficient to fire the entire multiple arcing section, the voltage will nevertheless remain limited to a value less than the protection level.

Figure 2 shows a circuit modified by the addition of varistors The rise in voltage due to the discharge delay of the arcing part-section is prevented by a varistor circuit. The varistors are connected in parallel with the arcing part-

sections FS2... FSi and for the time period until Ehe arcing partsections belatedly fire hold the voltage across them at an almost constant level determined by the varistor characteristics. As the varistors work virtually without any delay compared with an arcing section in air, the resulting impulse characteristic is virtually independent of the rate of rise of the voltage. Only the first arcing part-section FS1 has to fire by natural gas discharge. However, in a multiple arcing section, the firing voltage of the first arcing part- section FS1 can be set to a value well below the protection level.

- 9 The varistors are sized in accordance with the following relationship: (n-1) Ur + UAK < US n: number of arcing sections Ur: residual voltage of the varistor UAK: voltage on the uppermost arcing part-section FS1 given by the anode and cathode drop.

Us: protection level of the multiple arcing section.

By means of this circuit using varistors, advantageously the protection level is maintained safely even when the rate of rise of the voltage impulse is very high.

The invention is not restricted to the embodiment but is widely variable within the framework of the disclosure.

All new characteristics disclosed in the description and/or

the drawing both singly and in combination are considered to be fundamental to the invention.

Claims

- 10 CLAIMS:

1. Arcing section capable of carrying lightning current with several arcing sections connected in series, the arcing section consisting of n arcing part-sections (FS), whose arc drop voltage is brought to a level of n times the arc drop voltage of one arcing part-section by the series connection of the arcing part-sections (FS), and the arcing part-

sections (FS), with the exception of the first arcing section (FS1) to operate in the event of a lightning strike, being wired with impedances, in particular capacitances, so that the arcing part-sections (FS) break down successively, the second and every other arcing section (FS2 - FSN) being connected directly to a common reference potential, in particular earth potential, via the impedances and impedances of equal size being used in each case, characterized in that the sizing of the control capacitors is carried out in accordance with the following formula: (n-l) x CE = k x CL x - where n is the number of us capacitors, CE each control capacitor, k a safety factor l, CL the capacitance of the conductor from the arcing section to the source of the overvoltage, u the peak value of the overvoltage and us the protection level of the arcing section.

2. Arcing section according to Claim l, characterized in

that the arcing part-sections, with the exception of the first arcing part-section FS1, are provided with varistors, which are connected in parallel with each of the arcing part-sections (FS2 to FSN), the varistors being sized according to the following relationship: (n-1) Or + UAK US,

- 11 where n is the number of arcing sections, Or the residual voltage of the varistor, UAK the voltage of the first arcing section FS 1 given by the anode and cathode drop and Us the protection level of the multiple arcing section.

3. Arcing section capable of carrying lightning current with several arcing sections connected in series substantially as hereinbefore described with reference to the accompanying drawings.