Faulty Line Selection Method Based on Comprehensive Dynamic Time Warping Distance in a Flexible Grounding System

A flexible grounding system is a system in which the neutral point of the power supply is grounded via the arc suppression coil in parallel with a low-resistance resistor. When operating normally or a temporary ground fault occurs, the arc suppression coil is used for grounding, whereas the small resistance is switched on when a permanent ground fault occurs. At present, the problem of low protection sensitivity when a high-resistance ground fault occurs in a flexible grounding system has not been solved yet. According to the characteristics of low waveform similarity between the faulty line and the non-faulty line when a single-phase grounding fault occurred, a new faulty line selection method based on a combination of Dynamic Time Warping (DTW) distance and the transient projection method is proposed in this paper. Firstly, the fault transient signal is extracted by a digital filter as a basis for faulty line selection. Secondly, the transient zero-sequence current of each line is projected onto the busbar transient zero-sequence voltage, and the projected DTW distance of each line is calculated. Finally, according to the calculation formula of waveform comprehensive similarity coefficient, the Comprehensive DTW (CDTW) distance is obtained, and the top three CDTW distance values are selected to determine the faulty line. If the maximum value is greater than the sum of the other two CDTW distance values, the line corresponding to the maximum value is judged as the faulty line; otherwise, it is judged as a busbar fault. The simulation results based on MATLAB/Simulink and field data test show that the method can accurately determine the faulty line under diverse fault conditions.

Impact of Lightning Protection Grounding System on the Ground Surface Potential of Substations

Grounding device is an indispensable facility for lightning protection of buildings. Nowadays, SGCC (State Grid Corporation of China) is promoting steel structure substations, which are made of metal as a whole including the roof. There are now several grounding approaches when the roof was struck by a lightning flash, including external grounding, nearby grounding, separate grounding and common grounding. This paper took a metal structure substation in Nanjing as an example and calculated its ground potential in case of different grounding system. We came to such conclusions: 1) For substations of separate grounding system, the ground potential after a lightning strike could reach as high as 743.5kV and 230kV with a single earthing electrode and multiple electrodes respectively. 1000μs after the strike, the ground potential is 91.57 kV, which is still a significant threat to humans and equipment inside. 2) Nearby grounding and external grounding are both common grounding system. The peak of ground potential after a lightning strike is 101.4kV and 109kV respectively, much lower than that of separate grounding system. They also have similar waveform and peak time. 3) 3500μs after the lightning strike, the ground potential all over the grid is around 36V. 4) Separate grounding is not a sound choice of grounding system for steel structure substations. From the perspective of cost and discharging capacity, nearby grounding is the most reasonable scheme for a steel structure substation.

Design and Analysis of Earthing System for Wind Turbine Generators from Lightning Discharge Currents

<p>Currently, wind power production is undergoing rapid growth due to the escalating interest in green energy generation. As a result, generators are now choosing to locate wind turbine generators (WTGs) in areas where there is more lightning activity, and earthing problems can be exacerbated further by the soil resistivity being higher than where turbines are usually located. In addition, the desire to capture more energy from the wind has given way to larger WTGs, further increasing the probability of lightning strikes to the structure. This heightened regularity has emphasized the need for an effective grounding system, capable of dissipating the large currents discharged by the lightning into the lightning protection system. This “effective grounding system” must offer a low impedance by limiting the ground potential rise, which is critical due to the wider frequency content of the lightning discharge currents (ranging from DC to several MHz). The design of an effective grounding system for WTGs depends on the calculation of the minimum length of the earth electrodes, soil resistivity and its frequency-dependency, and the impact of WTG foundation. The calculation of the length of earth electrodes needs an accurate measurement of soil resistivity and modeling of the measured resistivity. Hence, this research considers the measured soil resistivity values of an Australian wind farm and presents an analysis of the soil stratification to identify the optimum soil models. The influence of the soil layers on the WTG grounding system is also investigated to install the earth electrodes. As the resistivity of the soil is frequency-dependent, an analysis is performed to evaluate the effect of the frequency-dependent soil parameters on the WTG grounding system at various frequencies of lightning discharge current. In addition, the impact of the rebar of the WTG foundation on the grounding system is evaluated as the rebar shares the lightning discharge currents. The effective length of the earth electrodes is frequency-dependent, and rebar determines the impedance of the grounding system at high-frequencies. The next step in the grounding design is the design of earth electrodes. The current dissipating capacity of the earth electrodes depends on soil resistivity, dimensions of the earth electrodes, and burial depth of the electrodes. However, the traditional practice of designing earth electrodes is based on the soil resistivity alone, considering the uniform soil resistivity model. The conventional method of designing earth electrodes based on the uniform soil resistivity is not practical due to non-homogeneous behavior of the soil resistivity. To enhance the WTG earthing system design, this research proposes a novel method to calculate the minimum length of an earth electrode for uniform and two-layer based soil models considering electrode dimensions and burial depth. The grounding impedance achieved when electrode lengths are calculated using the proposed method is compared to grounding impedance values computed using the conventional method. This comparison shows that the proposed method is an improvement on the current convention. In particular, the proposed method gives a grounding impedance value of less than 10 Ω at low frequencies for all soil resistivity values. This results in a reduction in the potential rise of up to 64% compared to the peak potential value in the conventional method. The benefits offered by the proposed method mean that it can be employed to calculate electrode lengths for the required resistance values based on soil resistivity, electrode dimensions, and burial depth. Such a design may serve as a starting point for an engineer wishing to design a WTG earthing system. Another challenge noted is the practice of assessing the effectiveness of the WTG grounding system. The conventional method is based on achieving a low-frequency resistance of 10 Ω according to the standard IEC 61400-24 and the performance of the grounding system at high frequencies is not considered. Hence, identification of the high-frequency components of the relevant lightning discharge currents is important to understand the performance of the grounding system. An analysis of the wind turbine earthing system for different lightning discharge current wave shapes is performed considering the lightning current waveforms and parameters mentioned in the IEC 61400-24 standard and evaluated the various frequency components and their influence on the WTG grounding system. It is identified that the impedance of the grounding system is minimum for the first short positive stroke current parameters for all the soil resistivity values compared to the first short negative and the subsequent short current wave shapes, although the peak current magnitude is highest for this wave shape. From the analysis of WTG grounding system based on various parameters, this research presents a procedure for assessing the effectiveness of WTG lightning protection system with a focus on the grounding system. It is identified that the effectiveness of the grounding system can be improved by proper design of earth electrodes, optimum soil stratification, and selecting low resistivity soil sites. Finally, various earth electrode configurations are evaluated to identify the better electrode configuration for WTG grounding system. This thesis provides an in-depth analysis of WTG grounding systems to protect WTGs from lightning strikes. The contributions of this research will help wind farm architects to design effective grounding systems leading to effective lightning protection systems. Finally, the contributions will help to increase the adoption of wind power, resulting in more renewable energy generation. The outcome of this research can be realized to reduce the downtime of WTGs by incorporating the effectiveness of lightning protection system component into the wind farm optimization process. Also, a generalized procedure for calculating the minimum length of earth electrodes for all the soil models can be developed in the future.</p>

Design and Analysis of Earthing System for Wind Turbine Generators from Lightning Discharge Currents

<p>Currently, wind power production is undergoing rapid growth due to the escalating interest in green energy generation. As a result, generators are now choosing to locate wind turbine generators (WTGs) in areas where there is more lightning activity, and earthing problems can be exacerbated further by the soil resistivity being higher than where turbines are usually located. In addition, the desire to capture more energy from the wind has given way to larger WTGs, further increasing the probability of lightning strikes to the structure. This heightened regularity has emphasized the need for an effective grounding system, capable of dissipating the large currents discharged by the lightning into the lightning protection system. This “effective grounding system” must offer a low impedance by limiting the ground potential rise, which is critical due to the wider frequency content of the lightning discharge currents (ranging from DC to several MHz). The design of an effective grounding system for WTGs depends on the calculation of the minimum length of the earth electrodes, soil resistivity and its frequency-dependency, and the impact of WTG foundation. The calculation of the length of earth electrodes needs an accurate measurement of soil resistivity and modeling of the measured resistivity. Hence, this research considers the measured soil resistivity values of an Australian wind farm and presents an analysis of the soil stratification to identify the optimum soil models. The influence of the soil layers on the WTG grounding system is also investigated to install the earth electrodes. As the resistivity of the soil is frequency-dependent, an analysis is performed to evaluate the effect of the frequency-dependent soil parameters on the WTG grounding system at various frequencies of lightning discharge current. In addition, the impact of the rebar of the WTG foundation on the grounding system is evaluated as the rebar shares the lightning discharge currents. The effective length of the earth electrodes is frequency-dependent, and rebar determines the impedance of the grounding system at high-frequencies. The next step in the grounding design is the design of earth electrodes. The current dissipating capacity of the earth electrodes depends on soil resistivity, dimensions of the earth electrodes, and burial depth of the electrodes. However, the traditional practice of designing earth electrodes is based on the soil resistivity alone, considering the uniform soil resistivity model. The conventional method of designing earth electrodes based on the uniform soil resistivity is not practical due to non-homogeneous behavior of the soil resistivity. To enhance the WTG earthing system design, this research proposes a novel method to calculate the minimum length of an earth electrode for uniform and two-layer based soil models considering electrode dimensions and burial depth. The grounding impedance achieved when electrode lengths are calculated using the proposed method is compared to grounding impedance values computed using the conventional method. This comparison shows that the proposed method is an improvement on the current convention. In particular, the proposed method gives a grounding impedance value of less than 10 Ω at low frequencies for all soil resistivity values. This results in a reduction in the potential rise of up to 64% compared to the peak potential value in the conventional method. The benefits offered by the proposed method mean that it can be employed to calculate electrode lengths for the required resistance values based on soil resistivity, electrode dimensions, and burial depth. Such a design may serve as a starting point for an engineer wishing to design a WTG earthing system. Another challenge noted is the practice of assessing the effectiveness of the WTG grounding system. The conventional method is based on achieving a low-frequency resistance of 10 Ω according to the standard IEC 61400-24 and the performance of the grounding system at high frequencies is not considered. Hence, identification of the high-frequency components of the relevant lightning discharge currents is important to understand the performance of the grounding system. An analysis of the wind turbine earthing system for different lightning discharge current wave shapes is performed considering the lightning current waveforms and parameters mentioned in the IEC 61400-24 standard and evaluated the various frequency components and their influence on the WTG grounding system. It is identified that the impedance of the grounding system is minimum for the first short positive stroke current parameters for all the soil resistivity values compared to the first short negative and the subsequent short current wave shapes, although the peak current magnitude is highest for this wave shape. From the analysis of WTG grounding system based on various parameters, this research presents a procedure for assessing the effectiveness of WTG lightning protection system with a focus on the grounding system. It is identified that the effectiveness of the grounding system can be improved by proper design of earth electrodes, optimum soil stratification, and selecting low resistivity soil sites. Finally, various earth electrode configurations are evaluated to identify the better electrode configuration for WTG grounding system. This thesis provides an in-depth analysis of WTG grounding systems to protect WTGs from lightning strikes. The contributions of this research will help wind farm architects to design effective grounding systems leading to effective lightning protection systems. Finally, the contributions will help to increase the adoption of wind power, resulting in more renewable energy generation. The outcome of this research can be realized to reduce the downtime of WTGs by incorporating the effectiveness of lightning protection system component into the wind farm optimization process. Also, a generalized procedure for calculating the minimum length of earth electrodes for all the soil models can be developed in the future.</p>

Modeling and calculation of SC currents for alternative group grounding system for the dc contact line supports

The problem of creating a mathematical model of the group grounding system of the contact line supports is considered. The paper considers an alternative way of organizing group grounding. For such a method of grounding, a model of a section of a DC railroad is proposed, which makes it possible to calculate the SC current. An analysis of the constructed model quality is carried out, an assessment of the calculation error according to the proposed method is given.

GROUNDING METHODOLOGY IN A 550 kV AC POWER TRANSMISSION LINE IN THE AMAZON - A CASE STUDY

Atmospheric discharges are indispensable for the electrical sector due to their responsibility on the shutdown of the power lines, what may trigger a sequence of events that led the interconnected electrical system to collapse. The aim of this case study is to demonstrate the development of a viable methodology in order to reduce the resistance values of the grounding system of the power lines, reducing shutdown occurrences due to returning disruptive discharges, or backflashover, mitigating the damages caused to the electrical system and to society, in order to improve the quality of the electrical power distribution. Considering the factors of implementation costs, technical environmental viability, the encompassment of this solution for other structures lines, and the reduction of the implementation percentage, it was concluded that the most adequate solution to implement a more robust grounding system in the transmission power lines is the solution 03 tested on the tower 585, with a reduction of 66,98%.

Experimental Investigation of Surge Propagation Characteristics on a Substation Grounding System

With the correct choice of the arrester by voltage class and compliance with the calculated protective distance without taking into account the propagation velocity of the current wave on the grounding grid, overvoltages exceeding discharge or residual voltage may occur on the protected equipment, in particular the transformer. Thus, when calculating the installation of the arrester that protects the substation from incoming lightning surges from a transmission lines, it is necessary to take into account the propagation of the current wave on the grounding grid. The propagation velocity of electromagnetic waves in a 150 kV substations grounding grid was measured. The measured wave propagation velocities are in the range of 50–100⋅106 m/s. Thus, the obtained velocity of wave propagation on the grounding grid used in service is several times less than the speed of light. The measured value correlates well with similar experiments conducted for buried conductors located in soils with similar parameters and the results of mathematical modeling for a grounding grid having similar dimensions and mesh size.