Active Mode Lighting Arrestor

ABSTRACT

The phenomenon of lightning is an exciting natural incident. However, its rate of occurrence can be as critical as it is electrifying. The magnitude of energy contained in lightning strikes is very high and can be destructive. In order to prevent electric power equipment from lightning, protection schemes like the use of lightning rods, ground wires and surge diverters are put in place to curtail its effects on electric equipment. This device is used for the protection of substations equipment against high traveling waves, by arresting the abnormal high voltage spike to the general mass of the earth devoid of affecting the continuity of supply. In this paper, a detailed design of a lightning arrester for protection of electric power system is presented.

CHAPTER ONE

1.0                                          INTRODUCTION

1.1                            BACKGROUND OF THE STUDY

Lightning is unpredictable and it is the most destructive of all elements associated with thunderstorms. It causes damage to many objects and systems such as electronic circuits, overhead and underground electric power and communication systems, buildings, boats, and aircraft and launch vehicles in flight. It is the most frequent cause of over voltages on distribution systems [1, 2]. The voltage of a lightning strike may start at hundreds of millions of volts between the cloud and earth. Although these values do not reach the earth, millions of volts can be delivered to the buildings, trees or distribution lines struck [3]. Lightning is a direct transient current that has been recorded to be up to 260,000 amperes and last for duration of up to 200 microseconds making it very hard to study [4]. According to [5], lightning strikes and thunderstorms during rainfall are very likely to occur frequently and hence protection of equipment especially transformers, that can be affected by their occurrence should be treated with utmost priority [6].

Lightning as a physical phenomenon, occurs when the clouds acquire charge or become polarized, thus creating electric fields of considerable strength between the cloud and adjacent masses such as earth and other clouds [5]. However, it takes a very conductive   atmosphere   below/about   50   km   owing   to the presence of ions created by both cosmic rays and the natural radioactivity for lightning to be triggered [7]. Studies carried out by Mowete and Adelabu [8] indicates that in the early times, the destructive effects of lightning strikes were limited mainly to high voltage (HV) power supply lines, but with the advent of mobile telephony services, information technology infrastructure concern expanded to include the increase in equipment fatalities occasioned by the absence of lightning protective systems. The choice of protection depends on the criticality of the load, relative size of the transformer compared to the total system load and potential safety concerns. Percentage differential protection is the most widely used scheme for the protection of transformers rated 10 MVA and above [9, 10].

Lightning arresters are essential devices of serious importance in areas prone to lightning strikes hazards like losses due to equipment damage [11, 12]. They are used to prevent the disastrous effects of lightning on buildings, power and communication systems, and equipment in general. As a result, the reliability of an electric power system is greatly affected by lightning strikes to such effects as line design, the frequency of lightning flashes, the magnitude of the lightning over voltages and the failure statistics of power system components as a major cause of power outages worldwide [13, 14, 15]. This is because, lightning damages power system equipment and many times renders them inoperable thereby making the system very unreliable. For instance, in 2003 United States, Canada and Europe suffered a series of blackouts, attributed majorly to lightning strikes leaving more than 60 million people without electricity [15, 16].

In addition, according to [17] a direct lightning strike on a power line or an induced voltage from a nearby strike may lead to line „„flashover‟‟ or failure of arresters, transformers, insulators, or other line hardware. Flashovers or equipment failure can result in an out-of-service line, which is a more technical term for an outage” [18, 19].

Different types of lightning arresters exist and they differ in material construction. They operate almost on the principle to provide low resistance path for the surges to the general mass of the earth.

Their selection depends on the factors like the material makeup, current, voltage ratings they can withstand, their reliability mostly and others follow. There are the rod arrester, multi gap, metal oxide, horn gap, expulsive type, valve type lightning arresters. The issue with the rod lightning arrester is that once the spark  occur, it may continue for some time even at low voltage. This is taken care of by the use of current limiting reactor in series with the rod. The presentation of the design of a valve type lightning arrester modelled after the IEEE model is the main concern of this work. Valve type of lightning arresters incorporate non-linear resistor. As the magnitude of lightning current/voltage is very high, the non-linear elements will offer a very low resistance to then passage of the surge which will rapidly go to the general mass of the earth instead of being sent back over the line. The non-linear resistors take up high resistance to stop the flow of current as the surge is over.

1.2                                   PROBLEM STATEMENT

Lightning phenomenon has resulted into several losses to both supply-side and load-side of the electricity infrastructure. When the travelling waves produced by lightning hit the windings of the transformer, it causes considerable damage. The inductance of the windings then opposes any sudden passage of electricity charge through it. Therefore, the electric charges “piles up” against the transformer (or generator). This induces such an excessive pressure between the windings that the insulation may breakdown, resulting in the production of arc. Also, the travelling waves produced by lightning surges can shatter insulators and wreck poles.

Whenever lightning strikes at any point in the network, it propagates from that point of incidence to other parts of the network. The propagation is such that the voltage surge magnitude increases as the voltage level decreases. How the lightning strikes and their effects on power distribution systems can be taken care of, where the results give a clear picture of how to eliminate the devastating impact, caused by lightning, by using lightning arresters. Quite a handful of research has investigated strategies for its mitigation.

1.3                                       AIM OF THE STUDY

The aims of this research are:

1. i) to discuss in detailed design of a lightning arrester for protection of electric power system

ii). To model the surge phenomenon and evaluate the effect of installed lightning arresters with regards to attenuation of surge in network.

1.4                      THE IMPACT OF LIGHTNING STRIKE

A lightning strike causes the ground potential in the area to rise to dangerous levels resulting in harm to personnel or destruction of electronic equipment in an unprotected environment. It also conducts a portion of the strike energy down the inner conductor of the coaxial cable to the connected equipment.

1.5                   ADVANTAGES OF LIGHTING ARRESTED

The advantages of lightning arrestor installation are as follows:

Minimizing Property Damage

A lightning arrestor installed on the exterior of a building can prevent structural damage to your property due to lightning and similar discharges. This can save you a huge amount of money if your property sees regular exposure to lightning due to location, materials, or other factors. It can also protect against secondary damage, such as strikes that hit nearby trees and cause branches to fall.

Prevent Damage to Lines

Outside of direct damage to your property, a lightning arrestor can help prevent damage to the fragile wires and cables outside. As with the more general protection against damage to the structure of your property, it’s a significant money saver—a lightning arrestor costs very little compared to what significant damage to the wiring of your property might cost you. More importantly, you’re looking at a substantial improvement in safety when you install a lightning arrestor on exposed wiring; a lightning strike may not be likely to pass into your building under anything but the most bizarre of circumstances, but it might damage wires enough to do serious harm.

Avoiding Outlet Surges

Smaller lightning arrestors serve a different purpose inside of a building, where they can be used to minimize the impact of surges at the outlet. These can range from extremely simple devices little more complicated than the average power strip to feature-rich pieces of advanced electrical equipment. Determining the appropriate fit for your needs can be difficult, but any of these devices when properly installed will protect occupants and devices against natural and artificial surges.

Electromagnetic Interference

Many general surge arresters and electricity filtering devices used in homes feature small-scale lightning arrester structures in combination with more advanced feature sets. This can help clean so-called ‘dirty’ power and keep your lines operating as they should even when storms roll in or other electromagnetic sources contaminate them. If you’re interested in EMI filtration, make sure you discuss the best solution to the problem with a qualified electrician.

Ease of Use

Compared to other solutions for dealing with surges, interference, and natural electrical phenomena, a basic lightning arrestor is usually far simpler to install and utilize to full effect. A licensed electrician can quickly install a lightning arrestor with no trouble, allowing you to reap the benefits of the system as soon as possible with minimal investment.