Study on Lightning Protection Measures for Distribution Lines and Customer Equipment against Back Flow Lightning Current from Radio Communication Station

Recently, with the expansion of communication network areas, the number of radio communication stations built in the neighborhood of customer houses has increased. If lightning strikes a communication radio tower, part of the lightning current flows into the distribution line and into customer houses. This may cause the failure of distribution lines or customer equipment. To protect distribution lines and customer equipment from lightning faults, it is necessary to analyze the surge phenomena in distribution lines and customer equipment and take appropriate protection measures. In this study, we examined the effect of lightning protection measures for distribution lines and customer equipment against lightning strikes to a communication tower. First, using an actual‐scale test distribution line, we measured the lightning current flowing into distribution lines and customer equipment. Second, we quantitatively examined the effect of lightning protection measures by lighting surge analysis while changing each parameter. From the experimental and analytical results, we show that the proposed protection measures can reduce the lightning current flowing into distribution lines and customer equipment.     

Surge transference through transformers

The article demonstrates the need for secondary surge protection on main utility tie transformers and low-voltage substation transformers. Investments in these surge protection devices are minimal and an insurance against insulation failures. A more elaborate transformer model could be used in EMTP simulations, however, the results based on the simplified transformer inductive/capacitance model are valid for practical purposes. The modeling of surge phenomena on EMTP is complex, and a modeling of all the possible surges of atmospheric origin or generated within a distribution system will be time consuming. The cost of providing secondary surge protection on unit transformers is rather small, though a coordination of the surge arrester characteristics is required. Considerations should be applied to the overvoltage withstand capability of solid-state protective devices, ASDs, and monitoring and control equipment, which is much lower than the insulation levels associated with the power equipment.     

Evaluation of currents and charges in low-voltage surge arresters due to lightning strikes

This paper presents an evaluation of the values of currents and charges absorbed by surge protective devices (SPDs) connected in low-voltage open-wire overhead distribution networks in the case of direct lightning strikes to primary lines. Also, some information about overvoltages magnitude is included. The calculations have been performed using the ATP (Alternative Transients Program). The modeling of the system components includes the insulation characteristics (voltage versus time to breakdown) of the primary and secondary insulators and a distribution transformer model for high frequencies which takes into account the load conditions. Some parameters of interest are taken into consideration in the analysis, such as ground resistances of poles and consumers, lightning strike position and crest value of the stroke current.     

Surge voltages and currents into a customer due to nearby lightning

This paper presents experimental results of lightning surges incoming into a customer due to lightning to an antenna of the customer, a pole and a ground nearby the customer, and briefly discusses lightning current distribution in the customer, a distribution line and a telephone line. Based on experimental results, modeling of each component is explained, and EMTP simulations are carried out. The ground voltage rise is represented by a mutual resistance between grounding electrodes. EMTP simulation results have been observed to agree qualitatively with the measured results, and it becomes possible to investigate lightning surges and current distribution in a customer by an EMTP simulation.     

Statistical analysis of lightning surges on distribution lines based on the observation

Probability distribution of surge discharging current of arresters provided a basis for conventional theory of grounding systems. In order to rationalize the grounding systems, it is necessary to grasp the statistical data of lightning surges on distribution lines caused by direct lightning strokes and indirect lightning strokes. Lightning phenomena on TEPCO's distribution lines had been continuously observed for the rationalization of lightning protection design of distribution lines. The observation had been carried out with still cameras and monitoring sensors of lightning surges. This makes it possible to discover new interesting facts that can be useful for rationalization of lightning protection design of distribution lines. Cumulative frequency distribution of conventional data is close to that of ZnO discharging current in the case of direct strokes and indirect strokes through TEPCO's observation. Moreover, to verify the cumulative current distribution in concrete poles, the authors have compared the cumulative distribution of current through ground lines with that of current through ground lines and concrete poles. The results show that the distribution of current through ground lines and concrete poles is larger than that of current through only ground lines for high currents exceeding 1 kA. This fact suggests that lightning surge current flows not only in ground lines but also in concrete poles. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 36–44, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20468     

变电站微机保护和监控系统电源干扰及抑制

雷击浪涌是低压电源线中发生最频繁的干扰源之一。为研究雷击浪涌对变电站微机保护和监控系统电源的干扰,首先通过分析电源线中雷击浪涌的入侵途径,提出了雷击浪涌危害的主要原因。然后基于过电压保护和电磁兼容两个方面的考虑,提出了低压电源线及低压电子设备的保护措施:一方面,根据低压电源系统防雷保护存在的问题,提出了完善低压电源系统的保护措施;另一方面,根据雷击浪涌的频谱中包含低频能量和高频能量的这一特征,提出了将瞬态抑制与滤波技术相结合的措施,即采用压敏电阻(MOV)消除低频能量,采用L-C低通滤波器滤除高频能量,从而有效地抑制雷击浪涌干扰。     

Mechanism of pole‐mounted transformer damage by backflow lightning and measures against the damage on low‐voltage distribution line

Pole‐mounted transformers are especially vulnerable to lightning damage. The progress of the information society imposes increasingly stringent requirements for the reliability of electric power supply, and this in turn necessitates a reduction in lightning damage to pole‐mounted transformers. Lightning protective devices (surge arresters) are now being installed around the primary bushing of the transformers, which has decreased the number of disconnections around the primary bushing due to lightning. But surge arresters installed on the primary side of the transformer cannot protect it against backflow lightning entering the secondary side of the transformer. The characteristic of transformer damage by backflow lightning is that the electromagnetic force produced by the current flowing into the secondary side deforms the transformer windings. This paper elucidates the mechanism of transformer damage by lightning flowing into the secondary side by comparing actual lightning damage cases with the results of verification tests using a short‐circuit generator. Effective countermeasures against transformer damage by backflow lightning are examined by EMTP calculations, which indicate that neutral grounding on the low‐voltage distribution line is the most effective way of decreasing the current flowing into the transformer. The lower the grounding resistance, the less current flows into the transformer. In addition, decreasing the voltage on the secondary side is important in order to protect the secondary‐side bushing. The calculation results indicate that surge arresters installed around the secondary side of the transformer are effective in decreasing the voltage on the secondary side. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(2): 1–11, 2010; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20921     

Analysis of coordination between primary and secondary protectors

This paper provides circuit models for analyzing the coordination between primary and secondary surge protectors. Although the analysis is performed in the context of lightning surges on telecommunication circuits, the models developed are generic in nature and can be used to analyze the interaction of cascaded surge protectors under voltages produced either by lightning or by power line disturbances. Equivalent circuits are developed for calculation of voltages and currents at primary and secondary protectors. Formulas are provided and procedures are described for achieving the best coordination between primary and secondary protectors. Two different configurations are analyzed for protection coordination. In the first configuration, the primary and secondary protectors connect between each conductor of the cable pair to ground. In the second configuration, a secondary protector is located between two conductors of a cable pair while the primary protector is located from each conductor to ground     

A theoretical study on the consequence of a direct lightning strike to electrified railway system in Sweden

Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this paper. Using this model, the induced voltages in each of the nine conductors at heights varying from 0.5 m (tracks) to 10 m above the ground are estimated. The effect of the finitely conducting ground is included using a time domain expression for the transient ground impedance that has better early time and late time behavior. The main interconnection between the conductors and the flashover strength of the supporting insulators is included in the simulations. A simple model for the arc channel during flashover of the insulators and the ionization of the soil around the pole foundations is also included in the model to assess the possible realistic surge voltage distribution in the system. It is shown in the paper that finite ground conductivity, interconnections between the conductors, arcing phenomena of insulation flashover and grounding of the poles decide the voltage/current distribution in the conductors. Simulations have been also carried out to determine the voltages on the lines and across the rails as function of distance from the point of strike as it could be a necessary data for deciding the possible future protection schemes. It was found that for a lightning stroke of 31 kA peak, large common mode and differential mode surges exist on the lines which could create excessive voltages between the line and neutral of the transformer and might pose a threat to the various low voltage equipments used for telecommunication, signaling and control.     

Investigation of VFT surges propagated into transformer and overvoltages applied to winding

Investigations were conducted on the VFT (Very Fast Transient) surges that propagate into a 500‐kV transformer. The disconnector restriking surge and ground fault surged were discussed. It was regarded that a large part of the surge voltage was applied just at the entrance of the transformer winding for the VFT surges. Thus, an equivalent circuit that models the windings was used for the analysis. The overvoltages that appear between the first winding sections at the entrance of the transformer were computed. The following was established. (1) The overvoltage between the first winding sections becomes greater when the magnitude of the voltage change at the transformer terminal is larger. The overvoltage between the first winding sections is not affected by the magnitude of the transformer terminal voltage. (2) For the disconnectors that are not connected directly to the transformer, the voltage change at the transformer terminal is not so large. (3) In the case of a ground fault at the GIS near the transformer, the voltage change at the transformer terminal is the same as that for a disconnector directly connected to the transformer. (4) In actual GIS, the disconnector that is connected directly to the transformer is not usually used. In this situation, the overvoltages that threaten the transformer insulation will not be generated by the restriking of the disconnectors. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 20–26, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10225     

Transformer insulation coordination using volt–time curve and limit–state surface formulation

This paper presents a novel method for the power transformer insulation coordination, based on the risk of failure analysis due to lightning surges, that uses its insulation strength volt–time curve and a limit–state surface formulation. The limit–state surface is derived in a novel way, from the optimal number of systematic numerical simulations of transformer terminal overvoltages—emanating from station impinging lightning surges—while accounting for the transformer insulation volt–time curve and surge arresters protective characteristics and disposition. The proposed method further employs a state-of-the-art transmission line (TL) and substation equipment models for lightning-surge transient analysis, constructed in the EMTP software package. It also uses the electrogeometric model of lightning attachment to TLs, in order to estimate the expected number of direct lightning strikes, along with a bivariate statistical distribution of lightning currents. The main aspects of the proposed method are demonstrated by means of the computational example featuring an air-insulated substation power transformer lightning insulation coordination. Simulation results exhibit many benefits of the proposed method. Sensitivity analysis further reveals different influences that the various model parameters have on the transformer insulation coordination design.     

Optimization of surge arrester's location

The lightning surges being considered the most dangerous events in power distribution systems, knowledge of the same allows to obtain a better selection and coordination of protection devices. Moreover, a better knowledge of lightning surges permits to optimize the location of device protection, to reduce the insulation costs of the installations, and to operate with risks of failure that are well known. The development of a computer application allowing determination of the optimal position of the surge arrester in power systems minimizes the risk of failure, thus permitting the selection of appropriate protection schemes for each network. As a consequence, protection costs are being reduced in accordance with the costs of the elements actually protected and the continuity of service to be achieved.     

Laboratory and analytical studies of the effects of multipulselightning current on metal oxide arresters

Multiple stroke lightning ground flashes can impose surges of exceptional severity on the arresters used to protect exposed distribution system equipment. This paper reports laboratory and analytical studies of the effects of representative multiple impulse currents on zinc-oxide surge arresters of distribution class. The results indicate that sextuple 8/20 μs currents can cause damage to arresters not evident with standard lightning current tests and so are worthy of inclusion in testing Standards     

Coordinating cascaded surge protection devices: high-low versuslow-high

Cascading surge protection devices located at the service entrance of a building and near the sensitive equipment are intended to ensure that each device shares the surge stress in an optimum manner to achieve reliable protection of equipment against surges impinging from the utility supply. However, depending on the relative clamping voltages of the two devices, their separation distances, and the waveform of the impinging surges, the coordination may or may not be effective. Computations with experimental verification of the energy deposited in the devices for a matrix of combinations of these three parameters is provided. Results show coordination to be effective for some combinations and ineffective for some others, which is a finding that should reconcile contradictory conclusions reported by different authors making different assumptions. From these results, improved coordination can be developed by application standards writers and system designers     

Surge Limiters for Vacuum Circuit Breaker Switchgear

The use of vacuum circult breakers In motor feeder applications (where motor terminal surge protection is not normally used) may require overvoltage surge protection within the switchgear to properly protect the motors. This need can be fulfilled by surge limiters designed for installation within the switchgear connected to the load side of the vacuum circuit breaker. This paper reviews the basic phenomena which cause vacuum switchgear related surges and dtscusses the need for surge limiters. This paper also describes the design of these surge limiters and provides information and performance data for their application.     

Characteristics of lightning surges observed at 77 kV substations

In order to improve power supply reliability, it is necessary to prevent lightning faults in transmission lines and substation apparatus. However, faults are caused occasionally in lower-voltage power systems, particularly at the 77 kV level. The governing factor for insulation strength of substation apparatus is the lightning impulse voltage, and it is necessary to know the voltage level and distribution in a substation caused by lightning surges in order to investigate rational insulation coordination. For this purpose, the authors measured lightning surges at two 77 kV conventional substations from 1990 to 1993. In this paper, the characteristics of induced lightning surges and back flashover lightning surges are described. Comparisons of related surge voltages at two substations, the power line phases in grounding faults, and the equivalent capacitance of the substations are also discussed.     

110- to 330-kV substation surge protection against lightning surge coming from transmission lines

A 110- to 330-kV substation protection against lightning surge coming from transmission lines is considered. It is shown that a transmission line always has a critical point, with resonance overvoltage appearing in transformer windings if a lightning strikes at this point. The transformer protection against resonance overvoltages can be implemented using ground wires around the critical point.     

浪涌抑制与电磁兼容

浪涌是低压电源线中最频繁发生的过电压和电流波动现象.研究电源线中的浪涌时不仅要分析它的电压幅值高低,还要分析它的电流和能量.电源线中浪涌抑制需要从过电压保护和电磁兼容两方面考虑.作者通过计算标准测试浪涌的波形和频谱,指出浪涌危害的主要原因和保护低压电源线与其上电子设备电磁兼容性的措施.最后计算了在交流电源中用氧化锌压敏电阻对浪涌进行限幅和泻流的一个实例.     

配电网故障及其控制措施研究

从配电网的结构以及内、外过电压水平和运行维护等方面对配电网故障进行了系统的研究，配电网内部过电压发生的几率较高，遭雷击的概率大、而其防雷措施薄弱，特别是缺少直击雷的保护措施，内部过电压和雷电过电压的共同作用对配电网的安全运行构成了很大的威胁，此外，恶劣的运行环境、不当的运行维护也是配电网故障频发的主要原因，提出了降低配电网故障的措施，如加强配电网的防雷保护，使用自动跟踪补偿消弧装置对铁磁谐振过电压和弧光接地过电压进行治理，降低配电网的故障建弧率，加强配电网的运行维护和设备管理等。     

Device for diagnostic monitoring of surge arresters

Basic reasons for the failure of nonlinear surge arresters are considered; most widely spread methods and devices for diagnostic monitoring of nonlinear surge arresters in the course of their operation are analyzed, and a new monitoring device registering discharge current pulses caused by lightning and switching voltage surges is proposed.