ITU-T防雷k25

刘跃龙

K.25：光缆的防护-(199605)

---The metallic elements of an optical fibre cable shall be continuous, i.e. it shall be connected across all splices regenerators, etc., along the length of the cable. The metallic elements shall be connected to the equipotential bonding bar (e.p.b.b.), either directly or through a SPD, at the ends of the cable一条光缆中的金属部件沿光缆长度方向应保持连续，即所有接头及再生器处的金属部件应接通。光缆终端的金属部件应直接接至等电位连接排或通过一个浪涌保护器件(SPD) 接至等电位连接排。

－Interconnection of single metallic components such as armouring, moisture barrier or strength member at splices or joints can be avoided in cables which do not use metallic conductors for signals or power (see Note in 7.4).

对于没有使用金属导线来传送信号或供电的光缆，可以取消金属部件(如铠装、挡潮层或加强构件)在接头处的连接。

primary failures: Primary failures on the optical fibre cable are those which cause the interruption of service(breakage of one or more optical fibres), an unacceptable increase in attenuation of the optical fibre or an interruption in the remote power supply, if the equipment is powered by metallic conductors inside the optical cable

光缆上的一次故障是指业务中断（一根光纤或更多光纤的断裂），光纤的衰减增加到不可容许的数值或远供电源中断（如果设备由光缆内的金属导线供电，）等故障。

secondary failures: Secondary failures on the optical fibre cable are those damages to the cable, such as the puncturing of the plastic protective covering (pinholing) and, in case, also of the metal sheath, which do not cause primary failures. 二次.故障光缆的二次故障是指那些光缆损坏，比如塑料保护层上的针孔缺陷等，但不导致一次故障的故障。

frequency of primary failures (Fp): Average annual number of expected primary failures in an optical fibre installation due to direct lightning flashes.

一次故障频度(Fp)直接雷造成光纤装置预期一次故障的年均次数。

risk of primary failures (Rd): Probable average annual loss of function in the optical fibre installation due to direct lightning flashes.

一次故障风险(Rd)直接雷造成光纤装置可能的年均功能损失。

tolerable frequency of primary failures (Fa): Average annual frequency of primary failures in an optical fibre installation not requiring additional protective measures.

一次故障容许频度(Fa)无需采取附加保护措施，预期的由直接雷造成光纤装置的年均一次故障次数的最大值。

tolerable risk of primary failures (Ra): Maximum level of the risk of primary failures (Rd) due to direct lightning flashes not requiring additional protective measures.

容许的一次故障风险(Ra) 无需采取附加保护措施，由直接雷造成一次故障风险（Rd）的最大限值。

direct lightning flash: A lightning to aerial cable or to the ground surface within the equivalent arcing distance D from buried cable.

直接雷雷击架空光缆，或雷击地表面与地埋光缆的距离小于等效电弧长度D。

direct lightning flash frequency (Nd): Expected average annual number of direct lightning flashes to an optical fibre installation

. 直接雷频度(Nd)雷电直击光纤装置的预期年均次数。

equivalent arcing distance (D): Average distance from buried cable at which a lightning can arc to the cable.

等效建弧距离(D)引起光缆建弧时，雷击点和地埋光缆之间的平均距离

failure lightning current (Ia): Minimum peak value of the lightning current giving rise to a direct arc on the cable and causing primary failures.

故障电流(Ia)引起与光缆直接建弧放电并导致一次故障的雷电流的最小峰值。

breakdown sheath current (Is): Current flowing in the metallic sheath which causes breakdown voltages between metallic elements inside the cable core and the metallic sheath.

屏蔽层击穿电流(Is)在光缆屏蔽层中流过，产生光缆芯内部金属加强芯与光缆金属屏蔽层间击穿电压，并导致一次故障的电流。

connection current (Ic): Minimum current flowing in the interconnecting elements that causes a primary failure due to thermal or mechanical effects.

连接电流(Ic)互相连接的元件导致一次故障的最小电流值，通过热能或机械效应来估计。

 

impulse current (Ip): Current to be used in the test for surge current resistibility of optical fibre cables. The test generator of this current is under consideration by IEC TC 81.

脉冲电流(Ip)测试光缆对浪涌电流.耐受能力时使用的电流。这种测试电流发生器目前在研究中。

 

interconnecting elements: interconnecting elements: Metallic elements connecting metallic sheath(s) or the metallic strength member(s) of optical fibre cable at joints and cable ends. 

互联元件在接头和光缆末端连接光缆金属屏蔽层或金属加强芯的金属元件。

test current (It): Minimum current injected by arc in the cable metallic sheath that causes a primary failure due to thermal or mechanical effects.

测试电流光缆的金属屏蔽层建弧导致一次故障的最小电流，通过热能或机械效应来估计。

breakdown voltage (Ub): Impulse breakdown voltage between metallic components in the core and the metallic sheath of the optical cable.

击穿电压(Ub)_.光缆芯内的金属加强芯与金属屏蔽层间的脉冲击穿电压。

damage correction factor (Kd): Factor which allows a conservative evaluation of the frequency of primary failures.

损坏修正系数(Kd)允许保守估计一次故障次数的系数。

surge protective device (SPD): A device that is intended to limit transient overvoltages and divert surge currents. It contains at least one non-linear component

浪涌保护器(SPD)用于抑制瞬态过电压以及分流浪涌电流的装置，它至少包含一个非线型元件。

equipotential bonding bar (E.B.B.): An electrically conductive bar whose electric potential is used as common reference, and to which metallic parts within the installation can be bonded.

等电位连接排(E.B.B.) 用于公共电位基准（参考）的良导体排。金属装置，外部导体，电力和电信线路及其他光缆可以与之连接。

direct lightning current to aerial cables (J): Minimum lightning current which strikes an aerial cable causing a flashover to ground.

架空光缆直接雷电流(J)雷击架空光缆导致对地闪络的雷电流的最小值。

exposed structure: A structure, e.g. telecommunication tower, high building, which needs to be protected against direct lightning strokes

暴露建筑物诸如电信塔和高层建筑等（按IEC 61024-1-1的要求）需防直接雷的建筑物。

keraunic level or thunderstorm days (Td): Number of days per year in which thunder is heard in a given location

雷暴日(Td)从年平均雷暴日数分布图获得的每年雷暴天数（见IEC 61024-1-1）

ground flash density (Ng): Average number of lightning flashes to ground per square kilometre per year, concerning the region where the structure or the optical fibre cable is located.

地面落雷密度(Ng)建筑物或光缆所在区域的平均每年每平方公里雷电对地闪络次数

lightning collection area: Area of ground surface which has the same annual frequency of direct lightning as the structure or the line.

引雷范围建筑物和线路有相同的每年直接雷次数的等效地表面区域。

Figure 1 represents the reference configuration for the optical fibre installations, where the connections with optical fibre cables between two Switches, between Switch and Line Termination and between Switch and line Equipment are shown

图一为光纤装置的参考结构，表示了交换机之间，交换机和线路终端之间，以及交换机和线路设备之间的光缆连接。

 

 

Construction characteristics of the cable光缆的结构和特征

This Recommendation applies to the following types of optical fibre cables:本标准适用于以下类型的光缆

–        –type A: cable with dielectric core but having no metal elements (dielectric or metal-free cable);

类型A：采用电介质芯线，但无金属部分的光缆（电介质，或无金属光缆）。

type B: cable with dielectric core and metal sheath or sheaths – there are no metal elements in the core of the cable which has a metal sheath (for example the moisture barrier) or a metallic supporting wire 第二类型B：有一层或几层金属屏蔽层与电介质芯线的光缆：芯线中没有金属成分，但是有金属屏蔽层（如防潮层）或金属支撑线。

type C: cable with metal elements in the core and with a metal sheath or sheaths – there are metal elements, such as conductors or strength members, in the core of the cable which has one or more metal sheaths;

类型C：有一层或几层金属屏蔽层,芯线中也有金属芯线的光缆：芯线中有金属线，比如导线芯或金属加强芯。

type D: cable with metal elements in the core and without a metal sheath

类型D：没有金属屏蔽层,但芯线中也有金属芯线的光缆。

For cable types B, C and D, the value of failure current (Ia) shall be evaluated, except for cables with more than one metal sheath.

光缆类型B，C和D需要估算故障电流(Ia)的可能值

5.2 Failure current for buried cable or aerial cable with earth connections of the metal sheath地埋或架空光缆金属屏蔽层与地连接的故障电流

 

 

 

 

 

 

7 Protective measures防护措施

7.1 General

The metallic elements of an optical fibre cable shall be continuous, i.e. it shall be connected across all splices, regenerators, etc., along the length of the cable. The metallic elements shall be connected to the equipotential bonding bar (E.B.B.) either directly or through a SPD, at the ends of the cable (see Figure 3)

光缆的金属部件应该是全长范围内连续的（它们应该是跨过.全部的接头，中继器等相连接），金属线应该直接或通过一个SPD，在光缆末端连接到等电位连接排（见图3）

If the E.B.B. of the subscriber building is not available, the metallic elements of the optical fibre

cable shall be connected to a dedicated E.B.B. inside the optical network termination.

如果用户建筑没有EBB，光缆的金属部分应该连接到光网络终端内一个指定的EBB上。

For optical fibre cables with metallic elements, the following protective measures are usually considered:对于有金属芯线的光缆，下列常用防护措施可以一起考虑使用：

– use of dielectric or metal-free cables;使用电介质或无金属光缆

– choice of the cable type for both buried and aerial cables;选择有较高故障电流值的地埋和架空光缆类型

– use of the shield wires for buried cables;仅对地埋光缆使用屏蔽线

– earthing of the metal sheath along the route for aerial cables (see 5.2);仅对沿架空光缆路径的金属屏蔽层接地

– route redundancy for both buried and aerial cables;地埋和架空路径冗余

– use of surge arresters for the protection of the metallic pairs of both buried and aerial cables使用避雷器对地埋和架空电缆的金属线对进行防护。

 

7.2 Dielectric or metal-free cables电介质的或非金属光缆

The use of dielectric or metal-free cables will prevent cable damage due to lightning.使用电介质的或非金属光缆可以防止光缆的雷击损害。

NOTE 1 – A non-metallic aerial cable is not directly susceptible to lightning damage. In fact, until now there has been no experience of such damage.注1： 非金属的架空光缆不易受直接雷击损害

NOTE 2 – For buried cables, the lowered resistance of the cable to moisture penetration and the difficulty of locating them during subsequent maintenance activities should be considered. Moreover metallic cables in the same ditch may be hit by direct lightning strikes and, as a consequence, the optical cable could also be destroyed (such damages are, until now, unknown). The same kind of problem may appear when a metal-free cable is accompanied by a metallic conductor (used to locate the optical cable).对于直埋光缆，需要考虑在后续维护中由于水分渗透降低光缆电阻以及进行定位的难度。另外，同一条沟中的金属光缆有可能被直接雷击中，因此，光纤也有可能被破坏（这种损害至尽未知）。同样的问题也可能发生在那些靠近树木架设，或附近有定位光缆用的金属导体的非金属光缆上。

7.3 Choice of cable characteristics for both buried and aerial installations地埋安装和架空安装对光缆特性的选择

Each cable type has its own specific value of failure current (Ia) which is evaluated as indicated in clause 5. The choice of the cable type implies a specific value of failure current (Ia) and, the higher the value of Ia, the lower the frequency of primary failure, as can be calculated in Annex A.每种光缆有其自身特定的故障电流值(Ia)，由第五章节指定的方法计算，选择光缆暗含一个特定的电流(Ia)， Ia值越高，Fp值就越低，与附录A计算的一样。

7.4 Use of shield wire for buried cables地埋光缆中屏蔽线的运用

The probability of damage to buried cables can be reduced by the use of shield wires. Shield wires intercept a portion of the stroke current thus reducing the amount of current striking the cable. For properly installed shield wires, the shielding factor value, denoted by η, implies that 100η% of the stroke current flows on the cable sheath. Shield factor values can be calculated with the method shown in Appendix I.

Improvement to the frequency of primary failures (Fp) due to shield wires can be calculated as follows:

Fp=Nd×P（≥Ia/η）

使用屏蔽线可以减少地埋光缆损害的可能性。

屏蔽线截流一部分故障电流，这样可以减少雷击光缆的电流值。

对于正确安装的屏蔽线，屏蔽系数值η指雷击电流的100η%流过光缆屏蔽层。

屏蔽系数值的计算方法可以用附录I介绍的方法计算。

屏蔽线对一次故障频率(Fp)的降低，可以按照下列公式计算：

Fp=Nd×P（≥Ia/η）

where:其中：

Nd expected average annual number of direct lightning flashes to the cable

; Nd是雷电直击光缆的预期年均次数。

p probability for the lightning peak current to be equal to or higher than Ia/η

P是雷电流峰值等于或高于Ia/η的概率。;

Ia failure current Ia是故障电流;

η shielding factorη是屏蔽系数.

NOTE – In the case of a metal free-cable core (i.e. there is only one metallic component, the sheath), the protection against induction from electrical lines can be obtained keeping the sheath(s) continuous at splices, providing earthing at repeaters and providing earth electrodes at splices only where required to limit the sheath to earth voltage to a value below the breakdown voltage limits.

注：在光缆芯线中不含金属（比如只有屏蔽层中含有金属成分）的情况下，对电力线感应的防护可以采用保持屏蔽层在接头处连续，中继器接地和仅在要求限制屏蔽层接地电压低于击穿电压的接头处采用接地极等方法。

The installation of shield wire(s) also allows the use of an another coordinated protection scheme, the interruption of the metallic sheath, i.e. the moisture barrier, at each splice or additionally at intermediate locations as required to keep the induced sheath to earth voltage values below the breakdown voltage limits

屏蔽线的安置也允许用另一种折中的防护方案，在每一个接头处或有接地要求的中间位置截断屏蔽层，例如防潮层，以保持屏蔽层感应对地电压低于击穿电压限值。

7.5 Route redundancy路径冗余

The overall service availability can be improved by implementing route redundancy using a second parallel route, which may be required for other reasons, such as the need for increased facilities. In such a case, the method presented in Bibliography [1] can aid in deciding the optimal route

separation to improve the overall service availability for buried and aerial cables.

使用并联的第二条路径来实现路径冗余可改进总体服务可用性，这可能是其他的原因，比如需要增加设备造成的。这种情况下，参考性附录[1]中介绍的方法有助于确定优化路由的间距，改进地埋光缆和架空光缆的总体服务有效性。

ANNEX A附录A

Frequency of primary failures一次故障频度A.1 Buried cable

A.1 Buried cable地埋光缆

The frequency of primary failures for buried cables (Fpb) is estimated with the following equation:

Fpb = Nd ⋅ p(Ia) [damages/year]                               (A-1)

为了评估每年的一次故障率，首先要根据以下公式确定直接雷的频度

 

 

 

 

ANNEX B附录B

Sheath breakdown current屏蔽层击穿电流

B.1 Buried cable地埋光缆

The sheath breakdown current (Is) of the cable with metal elements in the core and with one metal sheath, with or without an insulating protective covering, may be estimated from the following equation:对于金属屏蔽层和金属缆芯的光缆，不管是否存在绝缘保护外皮，其屏蔽击穿电流(Is)都可以用公式（B-1）估算

Is≅ Ub / ( K ⋅ R ⋅ ρ1/2) [kA]                                 (B-1)

where:

K = 8 [(m/Ω)^0.5] is the waveshape factor for lightning current (10/350 μs waveform)

其中：K=8是雷电流波形系数(10/350 μs 波形)单位[(m/Ω)^0.5]

 

R is the sheath resistance per unit length [Ω/km]R是屏蔽层单位长度电阻。

Ub is the breakdown voltage [V] of the cable, evaluated with the test indicated in C.2 Ub是光缆击穿电压其值通过C.2中的的实验得到。

ρ is the soil resistivity (Ω.m) ρ是土壤电阻率(Ω.m)

APPENDIX I附录I

Shielding factor屏蔽系数值

 

 

 

APPENDIX II附录II

Tolerable frequency of primary failures (Fa)一次故障频度容许值(Fa)

The damage caused by lightning to optical fibre installations may produce an unacceptable loss of services to the public. In this case, the decision whether or not to provide protective measures should be taken by a comparison of the actual value of frequency of primary failures (Fp) to the optical fibre installation with the limit value of the tolerable frequency of primary failures (Fa), fixed by each Network Operator.

由雷击引起的光缆装置的故障有可能导致某些公共服务不可接受的损失，这种情况下，是否提供保护措施必须比较一次故障频度值(Fp)和光纤装置的极限值，即一次故障频度容许值(Fa)才能由网络人员决定。

The value Fa can be estimated with the following equation:Fa可以通过下值计算

Fa=Ra/δ                            （ F-1)

where:

Ra tolerable risk of primary failuresRa是容许的一次故障风险极大值

δ relative amount of the expected losses per damageδ是一次故障损失预期值

The following values of Ra and δ are suggested:推荐的Ra 和 δ值如下

δ = 10−3

Ra= 10−4

Therefore:

Fa

= 0.1

APPENDIX III

Environmental factor (Ke)环境因子

The evaluation of Ke shall be performed based on the typical construction parameters of the region considered:环境因子应按基于考虑了区域内建筑类型参数执行。

– Urban area with tall buildings (above 6 floors): Ke = 0.01城区高建筑（6层以上）

– Urban area with medium buildings (between 3 and 6 floors): Ke = 0.1城区中层建筑（3-6层之间）

– Suburban area with houses (one or two floors): Ke = 0.5郊外的房子（1-2层之间）

– Rural area without constructions (flat ground): Ke = 1农村无建筑（平地）

 

– Rural area without constructions (top of hill): Ke = 2农村无建筑（丘陵山顶）