Protection of MV and LV networks against lightning. I. Basic information

The characteristics of lightning overvoltages initiated on overhead distribution lines vary greatly depending on the lightning stroke characteristics, the method of overvoltage generation (direct or induced), the orographic conditions (shielding effects) and the configuration of the line (medium or low voltage line, insulation level, presence of neutral conductors, earth resistance of the neutral etc.). In this paper the main characteristics of lightning overvoltages were clarified, as well as tools provided for the prediction of the number of lightning strokes to the lines. Waveshapes and peak-values of lightning overvoltages due to direct or indirect strokes have been described as well as their dependance on the line configuration, both for MV and LV networks. Since it is necessary for the Power utilities to protect their distribution networks in order to minimize the customers outages and the distribution apparatus damage caused by lightning, the information given in this paper consists of the basic knowledge which is helpful for the distribution engineers in order to determine the proper specific measures they have to take for this purpose in their LV and MV network

Lightning protection of distribution networks. Part II: Application to MV networks

The basic information for designers of lightning protection of MV and LV networks is given in Part I of the present publication. This Part II gives an application of this basic information to the lightning protection of MV networks containing overhead lines. As the overvoltages due to lightning reach important values, an economical and safe network design calls for extensive lightning protection. This general statement applies to high voltage as well as medium and low voltage networks. Overvoltage protection can be basically achieved in two ways: - reducing the amplitude and rate of occurrence of lightning overvoltages at the point of origin (e.g. through shielding the line conductors or improving the footing resistance of towers); - limiting the overvoltage at the equipment location (e.g. through surge arresters). In high voltage networks, both methods of protection are common. In MV networks shielding the conductors is generally not very effective. Due to the small clearance between the earth wire and the conductors, a direct lightning stroke will usually hit the conductors as well. In addition, induced overvoltages can be reduced only to a low extent by shield wires, as reported in [1]. For these reasons, the most effective protection against overvoltages in such networks is the use of surge arresters or spark gaps in the vicinity of the equipment. The paper gives guidance in the selection of rating and position of such protective devices and gives some indication on the effect of their use on the quality of the supply

PROTECTION OF MV AND LV NETWORKS AGAINST LIGHTNING, PART I: Common Topics

This brochure presents basic information and principles related to lightning protection of Medium Voltage (MV) and (LV) networks. The present material constitutes the first part of a 3-part guide. Parts 2 and 3, to be published later, will deal specifically with the application to MV (Part 2) and LV (Part 3) networks. This part provides first a survey of different sources of overvoltages, as well as a review of the most widely accepted and well established methods of evaluating the expected rate of direct lightning strokes and induced lightning overvoltages. The document describes in addition the characteristics of lightning overvoltages, general characteristics of surge protective devices, and earthing systems

Protection of Medium Voltage and Low Voltage Networks Against Lightning Part 2: Lightning protection of Medium Voltage networks

Overvoltages due to direct and indirect lightning events depend on several factors and are characterized by complex wave shapes. For this reason numerical codes have been developed, aiming at the evaluation of the lightning overvoltages on realistic distribution line configurations. These tools are of fundamental help in the protection scheme design and the insulation coordination of actual distribution systems, as well as in evaluating the overvoltages transferred through distribution transformers to the low voltage part of the system. The basic information for designers of lightning protection of MV and LV networks has been presented in the part 1 of this guide. This second part presents an application of the basic information to the lightning protection of MV networks containing overhead lines3. This part of the guide applies primarily to MV networks with system voltage in the range from 1 kV to 36 kV. It is relevant for higher system voltages as well, but it becomes gradually less relevant when the system voltage increases. It is thus not possible to specify an upper limit for the system voltage, but the guide should not be used for system voltages above 50 kV

LIGHTNING PROTECTION OF LOW-VOLTAGE NETWORKS

The improvement of the reliability and power quality levels of electric systems is a matter of increasing concern because today\u2019s equipment are much more susceptible to power quality issues than was equipment used in the past. Distribution networks are often located in areas with high ground flash densities, being therefore subject to lightning-caused power interruptions. As a significant number of line faults and equipment damages, as well as malfunction of customer electronic systems, is lightning-associated, many studies have been carried out, especially on medium voltage (MV) lines, aiming at obtaining a better understanding of the characteristics of the lightning overvoltages. More recently, special attention has been drawn to the transients on low voltage (LV) networks. Due to their much lower withstand capabilities in comparison with those of MV lines, LV networks are more prone to lightning electromagnetic interferences