ANALYSIS OF ELECTRICAL SURGES IN AJAOKUTA POWER SYSTEM NETWORK, NIGERIA

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ANALYSIS OF ELECTRICAL SURGES IN AJAOKUTA POWER SYSTEM NETWORK, NIGERIA

posted on SEPTEMBER 13, 2021

ABSTRACT

The study investigates the electrical surge effects and remedy in Ajaokuta Power System Network located in Kogi State in the North Central of Nigeria, to identify various causes of lightning strokes and highlight various associated effects and to determine surge intensity and magnitude, collection of surge data on distribution and transmission network. The approaches adopted is to develop a preliminary data collection that will address the identified data gap and to review comprehensively the electrical surge related losses and address the potential impact of electrical surge protective devices in mitigating these losses. Experimental investigations will be carried out and collation of available data associated with electrical surges and their impacts. The result of the data recording based on existing power system network revealed that the vast majority of the lightning strikes were less than 30kA. In the three years of monitoring six residences with 15 lightning surge events, only two lightning strikes were severe enough to cause damage at current values of 1.27kA and 1.09kA in 2013 and 2015 respectively. In this thesis causes of over voltages in Ajaokuta power system network are internal and external. Instances of extended high voltages are rare, but when they occurred significant damages are done. Therefore to maintain high quality power, wiring, grounding, bonding and installation of surge protective devices are necessary to prevent over voltages from this power system network.

CONTENTS

Page

DECLARATION                                                                                                                       ii

CERTIFICATION                                                                                                                    iii

DEDICATION                                                                                                                          iv

ACKNOWLEDGEMENT                                                                                                         v

ABSTRACT                                                                                                                              vi

CONTENTS                                                                                                                             vii

LIST OF TABLES                                                                                                                    xi

LIST OF FIGURES                                                                                                                 xii

LIST OF PLATES                                                                                                                   xiv

LIST OF ABBREVIATIONS                                                                                                  xv

CHAPTER ONE: INTRODUCTION                                                                                    1

CHAPTER TWO: LITERATURE REVIEW                                                                      8

CHAPTER THREE: MATERIALS AND METHODS                                                     45

CHAPTER FOUR: RESULTS AND DISCUSSION                                                         61

CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS                               70

REFERENCES                                                                                                                       72

 LIST OF TABLES 
      Table 2.1      Sources of Surges  Page   10
  Table 3.1  Technical Characteristics of the used surge Arresters  48
  Table 3.2  Surge data; April to October, 2013  50
  Table 3.3  Surge data; March to October, 2014  50
  Table 3.4  Surge data; March to October, 2015  51
  Table 3.5  Positive Lightning from 2013 to 2015  52
  Table 3.6  Negative Stroke from 2013 to 2015  53
  Table 3.7  F.F.R% July – August, 2013  55
  Table 3.8  F.F.R% August – September, 2014  55
  Table 3.9  F.F.R% August – September, 2015  55
  Table 3.10  Average F.R.R. for Regional Interval  56
 LIST OF FIGURES 
      Figure 2.1      Nature of Lightning Strokes  Page   9
  Figure 2.2  Typical utility capacitor switching transient Characteristics 
   reaching 134% voltage, observed up line from the capacitor  10
  Figure 2.3  Feeder current characteristics associated with Capacitor switching event  11
  Figure 2.4  Dynamic overvoltage characteristics during transformer switching  12
  Figure 2.5  Lightning Flash Density Map  13
  Figure 2.6  Typical Lightning Surge Current  14
  Figure 2.7  Voltage Waveform for Capacitor Switching Transient  15
  Figure 2.8  CWG 8/20 μs Current Waveform  29
  Figure 2.9  Protected Equipment  29
  Figure 2.10  Parallel Connected SPD  31
  Figure 2.11  Series Connected Filter  31
  Figure 2.12  Protected Equipment  32
  Figure 2.13  Silicon Avalanche Diode  34
Figure 2.14Number of Test Occurrences before Failure35
  Figure 2.15  Three-Stage Hybrid Signature Circuit  35
  Figure 3.1  Basic Structure of the Power System Network in Ajaokuta  44
  Figure 3.2  Location of SPD in the switchboard (in parallel)  48
  Figure 3.3  Cross-section drawing view of a polymer housed Surge arrester  48
  Figure 3.4  Schematic Diagram of Experiment No 1  49
  Figure 4.1  Stroke Peak Current; April to October 2013  57
  Figure 4.2  Stroke Peak Current; March to October 2014  58
  Figure 4.3  Stroke Peak Current: March to October 2015  58
  Figure 4.4  Stroke Peak Current Percentage (Positive lightning stroke)  59
  Figure 4.5  Stroke Peak Current Percentage (Negative Polarity)  60
  Figure 4.6  Region 1 %FFR July to August 2013  61
  Figure4.7  Region 2 %FFR August to September 2014  61
  Figure4.8  Region3 %FFR August to September 2015  61
  Figure 4.9  Tower Footing Resistance (OHM)  62
  Figure 4.10  Arrester Interval (KM)  63
 LIST OF PLATES 
      Plate 1.1      Ajaokuta Nigeria Latitude and Longitude  Page   6
  Plate 2.1  Circuit Breaker Failure Caused by surge Voltage  16
  Plate 2.2  Copper Busbar Melted by Surge Current  17
  Plate 2.3  Circuit Board Damaged Caused by Surge Voltage  17
  Plate 2.4  Micro Circuit Damage Caused by Surge Voltage  17
  Plate 3.1  Ajaokuta Nigeria latitude longitude  43
  Plate 3.2  Step for grid Lines  44
  Plate 3.3  Main Step –Down Substation I  44
  Plate 3.4  Surge Protector  45
  Plate 3.5  Earth Ground Tester (Fluke 1625)  45
  Plate 3.6  Meter Board of Transmission Station  46
  Plate 3.7  Main control Board of Transmission Station  47
  Plate 3.8  Export and Import Power at Transmission Station  47

LIST OF ABBREVIATIONS

µsecMicro-second
  EMI  Electromagnetic Interference
  FPRF  Fire Protection Research Foundation
  GDT  Gas Discharge Tube
GPRGround Potential Rise
  Hz  Hertz
  IEC  International Electro-technical Commission
  III  Insurance Information Institute
kAKilo-Amperes
  khz  Kilo-hertz
  L-G  Line to Ground
  L-L  Line to Line
MCOVMaximum Continuous Operating Voltage
  MOV  Metal Oxide Varistor
  NEC  National Electrical Code
  NEMA  National Electrical Manufacturers Association
NFPA N-G NIST NLDNNational Fire Protection Association Neutral to Ground National Institute of Standards and Technology   National Lightning Detection Network
PUPer Unit
  SAD  Silicon Avalanche Diode
  SCCR  Short Circuit Current Rating
  SPD  Surge Protective Device
TOVTemporary Overvoltage
  TVS  Transient Voltage Surge Suppressor
  UL  Underwriter’s Laboratories
  VPR  Voltage Protection Rating
  • Background to the Study

CHAPTER ONE INTRODUCTION

Degradation, disruption and destruction are three “Ds” that affect power quality. Electrical power disturbances may be called a surge, sag, spike, swell, transient, fluctuation, interruption, or electrical line noise. All these electrical power disturbances are abnormalities and deviations from normal performance of voltage sources (Gustavo et al, 2003; Sukhdeo, 2013). These Electrical power disturbances may last for a short period or a long time (continuous).

In general, a surge is a transient wave of current, voltage or power in an electric circuit. In power systems in particular this is likely the most common context that we relate surges to a surge, or transient is a sub cycle over-voltage with duration of less than a half-cycle of the normal voltage waveform. A surge can be either positive or negative polarity, can be additive or subtractive from the normal voltage waveform, and is often oscillatory and decaying over time. Surges or transients are brief over-voltage spikes or disturbances on a power waveform that can damage, degrade, or destroy electronic equipment, industrial, or manufacturing facility, commercial building. Transient can reach amplitudes of tens of thousands of volts. Surges are generally measured in microseconds and can be internal over voltages or external over-voltages (Khalid, 2011; Teru, 2010).

Internal over voltages originate in the system itself and may be transient, dynamic or stationary. Those of a transient nature will have a frequency unrelated to the normal system frequency and will persist a few cycles only. They can be caused by the operation of circuit breakers when switching inductive or capacitive loads, “current chopping” when interrupting very small

currents or by the sudden grounding of one phase of a system operating with insulated neutral (Hasssan, 2017 and Makinde et al, 2014).

Approximately 70% of electrical threats are internally generated and the remaining 30% of issues are external over voltages that can be caused by atmospheric discharges such as static charges or lightning strokes and are therefore not related to the system (Nema, 2014). They are often of such magnitude as to cause considerable stress on the insulation and, in the case of lightning will vary in intensity depending on how directly the line is struck , i.e., directly by the main discharge, directly by branch or streamer, or by induction due to a flash passing near to but not touching the line. Power quality is measured by the interaction of electric power with electrical equipment (Dharmender, 2014; Mehdi et al, 2014).

This thesis is to ensure an uninterrupted supply of electricity that is (power quality) in Ajaokuta power system network. High quality power can be achieved by ensuring that wiring, grounding and bonding are up to standards. Once this is verified then the right power quality device is selected such as Surge Protective Devices (SPDs), low-pass filters, data and signal line protectors to prevent damage from surges and electrical line noise.

               Justification for the Study

Surges or over voltages have caused stresses, disruption and damages to numerous equipment and gadgets in Ajaokuta power system network, such as high and low voltage induction motors, synchronous motors, transformers, circuit breakers, reactors, capacitor banks, generators, contactors, relays, etc. Khalid (2011) presents the power quality problems, issues, such as power surge related international standard, effect of power quality problem in different apparatuses and methods for its correction. Iit-Bhu (2014) presents investigation of different types of premature failures that are observed during various full-scale testing of transmission line towers and their results are discussed in detail.

Importance of design assumptions and connection detailing in overall performance of towers were studied (MCoy, 2013). Due to the opening or closing of circuit breakers and disconnect switches in Gas Insulated Substations (GIS), especially in the pumped storage power stations, Very Fast Transient Over-Voltages (VFTO) are generated (Sukhdeo, 2013). The main causes of over voltages in power system are switching and lightning. The over voltages can damage the insolation of lines and equipment connected to the power system. In other to protect insulations and equipment of the power systems from the damaging effects of lightning over voltages, metal oxide surge arresters have been used.

Because of dynamic behaviour of the surge arresters, they cannot be simulated using non-linear resistors. Therefore, several models are proposed to simulate the dynamic properties of surge arresters. IEEE and pinceti models are the main models proposed that are for the simulation of the dynamic behaviour of surge arresters. In this thesis, for identification of surge arrester parameters and a novel algorithm have been proposed and then a comparison among IEEE model and pinceti model has been investigated (Mehdi et al, 2014). Mungkung et al. (2007) investigated the temporary increase in voltage in the transmission line system. Lightning is the most harmful for destroying the transmission line and setting devices so it is necessary to study and analyze the temporary increase in voltage for designing and setting the surge arrester. This analysis describes the lightning wave in transmission line with 115 kV voltage level in Thailand by using ATP/EMTP program to create the model of the transmission line and lightning surge. Because of the limit of this program, it must be calculated for the geometry of the transmission line and surge parameter and calculation in the manual book for the closest value of the parameter.

On the other hand, for the effects on surge protector when the lightning comes, the surge arrester model must be standardized as metropolitan electrical authority’s standard. The researcher

compared the real information to the result from calculation Shehab (2013) presents an overview of how the lightning strikes and their effects on power distribution systems can be modeled, where the results gave an understanding of how to eliminate the devastating impact, caused by lightning, by using lightning arresters.

Many conventional protective devices installed for protection of excessive fault current in electric power systems, especially at the power stations are the circuit breakers, tripped by over- current protection relay (Okundamiya et al., 2009). These devices the response-time delay that allows initial two or three fault current cycles to pass through before getting activated. Superconducting Fault Current Limiter (SFCL) is innovative electric equipment which has the capability to reduce fault current level within the first cycle of fault current. The application of the Fault Current Limiter (FCL) would not only decrease the stress on network devices, but also can offer a connection to improve the reliability of the power system (Makinde et al., 2014).

This research is investigate the effects of electrical surge and the possible remedy in Ajaokuta power system network. Consideration of three basic approaches which includes; experimental investigation would be carried out on lightning surges in the distribution lines in some residences of Ajaokuta Power System Network, to develop data bank for lightning stroke and magnitude of cloud to earth lightning strokes to be used as a factor in determining the required maximum surge current of SPDs. For this reason, the maximum surge current of an SPD could be selected based on perceived lightning stroke levels. In addition, a test would be carried out on the three 132kV transmission lines of Ajaokuta power interconnected system to determine the variation of surge arresters failure probability with tower footing resistance for each of the three case studies to be analyzed.

               Objectives of the Study

The overall aim of this study is to investigate the effects of electrical surge and the possible remedy in Ajaokuta power system network.

The specific objectives are to:

  •   identify various causes of lightning stroke and highlight various associated effect in electrical equipment;
    • determine the lightning stroke intensity and magnitude;
  • analyse the data obtained base on set time duration and area under investigation;
  • determine the variation of surge arresters failure probability with Tower Footing Resistance (TFR) at 132kV operation transmission lines of Ajaokuta and;
    • design a surge protection scheme (mechanism) for equipment.

               Scope and Limitation

This research focuses on the effects of electrical surge and it remedy in Ajaokuta power system network in Kogi State, Nigeria. It involves recent surge data collection and analysis in the distribution and transmission units to determine the SPDs locations and ratings required in facilities and residences.

               Research Methodology

Experimental investigation will be carried out in this study in order to achieve the desired objectives of this study as follows:

  • an experimental investigation would be carried out on lightning surges that flow in the distribution lines in some residences of Ajaokuta Power System Network. Lightning surge detectors shall be installed in six (6) residences and monitored for three years, 2013 to 2015 to ascertain the effects of lightning surge on the distribution lines;
  • data Bank Presentation From 2013 – 2015: This data Bulletin would provide objective data about lightning stroke intensity based on a scientific study. Since 1995 the power system network of Ajaokuta has set up the lightning data bank to collect data on the total number and magnitude of cloud to earth lightning strokes to be used as a factor in determining the required maximum surge current of Surge Protective Devices (SPDs). For this reason, the maximum surge current of an SPD could be selected based on perceived lightning stroke levels; and
  • tests would be carried out on the three 132kV operation transmission lines of Ajaokuta power interconnected system to determine the variation of surge arresters failure probability with Tower Footing Resistance (TFR) for each of the three case studies to be analysed; and to determine the arrester failure probability interval based on the transmission line, these lines shall be carefully selected due to: their high rate of failure during thunderstorms, their sufficient sufficient time in service and the significant different characteristics, such as ground flash density and the tower footing resistance which exist through their lengths, since they run through the same region.

               Thesis Arrangement

Chapter one is Introduction, which consist of Background to the study, justification of the study, objectives of the study, scope and limitation, research methods. Chapter two is the Literature Review, chapter three contains Materials and Method, which consist of three experimental procedures. Chapter four contains Result and Discussion, findings, contributions to the knowledge, and chapter five contains conclusion and recommendations.

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