Design And Analysis Of Over Voltage Protection System In A Distribution Network

INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Protection systems are vital components of any power system. Its goal is to detect and isolate faults when they occur. By doing so, safe operation of power systems can be achieved, extensive equipment damage can be avoided and the areas affected by faults can be minimized.
The overvoltage protection of distribution networks is quite challenging task. The traditional reason for overvoltage protection has been prevention of failure of expensive components like transformers. Along with increasing importance of power quality the effect of overvoltage protection to short interruptions and voltage dips is of great importance. This means that overvoltage protection should be deeply modeled and analysed as part of reliability based network analysis. For example, selection of using surge arresters instead of spark gaps in transformer protection is not necessary based on the transformer itself but the consequences of short interruption and voltage dips due to arcs in spark caps. This paper presents different types of strategies which can be applied in overvoltage protection planning but focusing mainly on the use of surge arresters which is been modeled in this work.

1.2 PROBLEM STATEMENT
Power distribution systems are directly linked to customers. Thus the distribution system plays an important role in the overall power system reliability and the perceived reliability to customers. By improving distribution protection systems such that sustained outage times can be reduced, power system reliability can be enhanced.
For every power distribution system lightning discharges are one of the most significant disturbances, since it can give origin to overvoltage and consequent influences on the quality of the power supply. Among several consequences of the incidence of any lightning discharge, one of the most significant is the transference of voltage surge between primary and secondary windings of any power distribution transformer. The degree of transference basically depends on the frequency response of the transformer (Cabral et al, 2010) as well as on its grounding impedance. Thus, several studies have been carried out by analyzing transferred or induced voltages due to lightning discharges through grounding systems (Visacro et al, 2012).
This work studies the analyses of such kind of overvoltage require the utilization of reliable modeling to represent all the elements involved in this process. In this work distribution transformer modeling is considered using surge arrester.

1.3 AIM AND OBJECTIVE OF THE PROJECT
This work is aimed carrying out an analysis of over voltage protection system in a distribution network.
The objective of this work is:
• Provide a solution to voltage in a power system.
• To presents a model for the analysis of overvoltage in power distribution network caused by lightning discharges.
• To carry out a simulation of overvoltage protection scheme using surge arrester.

1.4 SIGNIFICANCE OF THE STUDY
As a student of electrical and electronic engineering, working on this project has expose my knowledge to causes and solution to over-voltage protection system in a distribution network. It has made me to understand how surge arrester can be model in a distribution network.

1.5 SCOPE AND LIMITATION OF THE STUDY
The scope of this work covers the modeling of a overvoltage protection scheme based on the use of surge arresters on a distribution network. In this work surge arresters are mounted on an additional wood crossarm, considerably closer to the transformer terminal bushings. The total length of the surge arrester connection conductors is 6 m and 1.1 m for the common practice and the alternative protection scheme, respectively.
There are different methods of carrying out a protection scheme in a power system, but in this work only the use of surge arresters was studied.