The effect of back spark phenomenon in transmission lines on distance relay performance

Dissertation for Master Degree in Electrical Engineering

Power Orientation

Abstract

In this thesis, the effect of return arc phenomenon on the performance of distance protection relay is evaluated. Because the lightning striking the tower or the wire guard in the transmission lines can cause a return arc on the chain of insulators. Therefore, at first, different methods of modeling the parameters and equipment of transmission lines, including the mast, insulator chain, and lightning source, and the return arc phenomenon (primary and secondary arc models) are examined using important references in this field, and several models are introduced for each of these parameters. Then the effect of return arc on distance relay performance is investigated. In this way, the most important step is the simulation of the implementation steps of these models in the sample network by the EMTP-RV software.

Keyword - lightning, high voltage transmission lines, return arc, distance protection relay.

1 statement of the problem and reasons for investigation

One of the important factors in the occurrence of automatic transient outages of overhead transmission lines [1] is the collision of lightning [2] with line equipment. The statistics extracted from the investigation of the incidents of the western regional power grid lines show that on average, more than 70% of the automatic outages of the lines each year occurred due to lightning strikes and mainly the return arc phenomenon [3]. The diagram (Figure 1-1) shows the average contribution of each factor in the occurrence of automatic outages of energy transmission lines in each year [1] and [2].

Lightning strikes on lines can cause short circuit and automatic disconnection of overhead transmission lines in two ways:

E lightning strike on the main conductors of the line, which induces potential in the conductors and in different parts of the tower, especially in the chain of insulators [4] The discharge from the conductor to the ground parts and in the form of a phase-to-ground connection, will cause the automatic interruption of the line. In lines that do not have a protective wire or the protective wire does not completely cover the phase conductors, this type of connection occurs more.

E in transmission lines, when the tower or aerial ground wire [5] is hit by lightning, due to the passage of the lightning current, a potential difference between the tower and the conductors of the phases is created, and if this potential difference is large enough, a spark from the tower A phase conductor is established, and this phenomenon is called a return arc [3], [4] and [5]. The maintenance and protection of these systems against events and incidents have always been and are inevitable. Therefore, the error in the airlines should be cleared as soon as possible in order to prevent the spread of widespread effects that can greatly affect the consumer. To fulfill these conditions, each section of the line is opened by means of a protection relay that is automatically placed on the power switch on each side of the line to isolate the line from fault. The distance relay [6] is also used as the main protection [7] and the protection of the subsequent parts [8] of the transmission line. 1-2 objectives of the thesis Research on the factors of return arcing in the transmission lines and its effect on the performance of the distance relay has been evaluated. Due to the scope and importance of the subject, this research can include different parts.

The objectives of this thesis can be generally divided into two categories:

1-2-1 accurate modeling of the transmission line, return arc and distance relay

Because in practice, it is very difficult and almost impossible to calculate the error caused by the return arc phenomenon on the distance relay in the power transmission system. Accurate modeling of each of the mentioned items is very important. Mathematical models have been simulated by EMTP-RV [9] software.

1-2-2 Investigation and analysis of the effect of the return arc phenomenon on distance relay performance

In this thesis, the effects of the return arc phenomenon on the transmission line are investigated and analyzed based on the following parameters.

E transmission line.

E mast.

E chain Insulator.

E lightning.

E fault arc.

E Distance relay.

The second chapter of each of the mentioned cases has been studied and discussed.

In the third chapter, the studied transmission line and its related components and the models used in the simulation of these components are discussed. The simulations of this chapter have been done using EMTP-RV software. The fourth chapter analyzes the results obtained from the simulations. In the fifth chapter, the results have been obtained and the suggestions have been presented. done)

2-1 Introduction

Lightning is one of the most important causes of power outages and destruction of power transmission network equipment, and lightning strikes with transmission network equipment can lead to huge economic damage and long-term blackouts. In the lines, due to the extension of the transmission line, there is a possibility of lightning striking it directly, which causes risks for the insulation system of the transmission line (insulators). Transmission lines, high voltage [10] (voltage level between 72.5 and 245 kV) and very high voltage [11] (voltage level between 300 and 765 kV) according to the international standard IEC [12] are used as "highways" to transfer electricity from the power plant to the load center (Figure 2-1). Although transmission lines are equipped with aerial wire guards to limit direct lightning strikes, there are still disturbances due to direct and indirect lightning strikes. Statistics show that more than 70% of all faults in overhead transmission lines are temporary, and the phase arc fault to the ground is due to direct or indirect lightning strike. Figure (2-1): Overhead transmission line as a part of the power system Fault in overhead lines should be cleared as soon as possible in order to prevent widespread effects that can affect the consumer to a large extent. To fulfill these conditions, each part of the line is opened by means of a protection relay that is automatically placed on the power switch on each side of the line to isolate the line from fault. System protection in high voltage and very high voltage transmission lines is divided into main and backup protection according to their function. Distance protection as the main protection is usually the distance relay and the backup protection is the high current relay to increase the system protection (Figure 2-2). After that, the adjustment and coordination between the distance relays are important to achieve the best performance in line protection in each section. The single-phase autocloser [13] complements the main protection in high voltage and very high voltage power systems, so that after the fault is resolved The recloser will reconnect where the breaker has disconnected. Determining the connection time of the single-phase auto-recloser in these types of relays depends on knowing the final time of the fault arc shutdown [14]. According to these needs, researchers have made a great effort to understand the physical nature of the fault arc, to accurately model this phenomenon, and to implement these models. Studies on the fault arc began in the early 20th century (1902) [6]. Due to the lack of detailed study of fault arc theory at that time, experts did not have enough information and most of the knowledge was experimental and limited to specific cases. At that time, no information was available on high-current arcing. The first relationship (voltage-current) for arc fault was presented in the same years. In the 20s, these equations became more complete. The first equation that describes the characteristics of the fault arc more fully was introduced in 1945 at the Westinghouse Institute, and the first computer simulation of the single-phase fault arc to the ground took place at the end of the 70s at Beth University [15] in England [7]. These simulations have been completed in the following years [8]. In all works, EMTP-RV software has been used to implement the proposed arch models and simulate them. Based on the opening and closing conditions of the phase fault, the fault arc can be divided into primary[16] and secondary[17]. Primary arc is a strong arc developed by high short circuit current, arc length is constant. The length of the secondary arc can be more than 10 times that of the primary arc. However, unlike the primary arc, random variations of the arc parameters significantly affect the secondary arc.