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
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF PLATES xiv
- Background to the Study 1
CHAPTER TWO: LITERATURE REVIEW 8
CHAPTER THREE: MATERIALS AND METHODS 45
CHAPTER FOUR: RESULTS AND DISCUSSION 61
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS 70
| 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 2.14 | Number of Test Occurrences before Failure | 35 |
| 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
| µsec | Micro-second |
| EMI | Electromagnetic Interference |
| FPRF | Fire Protection Research Foundation |
| GDT | Gas Discharge Tube |
| GPR | Ground Potential Rise |
| Hz | Hertz |
| IEC | International Electro-technical Commission |
| III | Insurance Information Institute |
| kA | Kilo-Amperes |
| khz | Kilo-hertz |
| L-G | Line to Ground |
| L-L | Line to Line |
| MCOV | Maximum Continuous Operating Voltage |
| MOV | Metal Oxide Varistor |
| NEC | National Electrical Code |
| NEMA | National Electrical Manufacturers Association |
| NFPA N-G NIST NLDN | National Fire Protection Association Neutral to Ground National Institute of Standards and Technology National Lightning Detection Network |
| PU | Per Unit |
| SAD | Silicon Avalanche Diode |
| SCCR | Short Circuit Current Rating |
| SPD | Surge Protective Device |
| TOV | Temporary 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.