Investigation of overvoltage on square, rectangular and L-shaped ground grids of high voltage substations by ATP/EMTP

Ground grid system is important for preventing the hazardous effects of overvoltage in high voltage substations due to fault current perhaps from lightning strike or device malfunction. Therefore, this study aimed to investigate the effects of overvoltage on square, rectangular and L-shaped ground grids with ground rods being distributed in mesh-pattern by using alternate transients program/electromagnetic transients program (ATP/EMTP) program. The models were simulated in the cases that 25 kA-fault current being injected into the center or one of the corners of ground grids. The results showed that the highest level of overvoltage (6.3349 kV) was detected at the corner of rectangular ground grid when the fault current was injected into its corner. However, the lowest level of overvoltage was found when the fault current was injected into the center of square ground grid. The results from this study indicated that ATP/EMTP program was useful for preliminary investigation of overvoltage on ground grids of different shapes. The obtained knowledge could be beneficial for further designing of ground grid systems of high voltage substations to receive the minimal damages due to fault current

Analysis of Lightning Strike Impulse Strategies in Electricity Distribution Channels Utilizing Mixed Lines

To ensure the operational security of these systems and to give higher quality electricity to all users, it is important to assess the transient behavior of electric power transmission and distribution systems when they are challenged to varied forms like lightning discharges, which in this research is focused to determine the effect by utilizing the mixed line configuration on the impulse voltage of lightning strike on the 20 kV distribution line. This experiment was carried out using sources of data through channel documentation on Makassar City Polda Feeders with an airway length (SUTM) of 7.8 km and a cable channel length (SKTM) of 2 km obtained from PT. PLN (Persero) Makassar Branch and then input into the ATP-EMTP simulation process with either a simulation of 20 and 50 kA strikes at distances of 2.5, 4.5 and 6.5 km with lightning impulses of 1.2/50 and 8/20 µs. configuration of lines at the transition point and also the end of the cable channel depending on the magnitude of the lightning current, the location of the strike, and the lightning impulse. Lightning peak current is proportional to the voltage response at the transition point and the end of the cable, and the effect on lightning impulse peak voltage is generated at the transition point and the end of the cable. According to research results of initial research, the use of mixed channel lines can decrease the impulse voltage is 20 kV distribution lines

Proposal of analysis method to reduce back-flashover rate taking account of tower footing resistance

The number of lightning stroke on the tower of the 150 kV Koto Panjang-Payakumbuh transmission line located the rocky area has been observed. The high value of tower footing resistance indicates the occurrence of the back-flashover in the transmission line at intensity of 74%. The back-flashover occurrence is dominantly triggered by the tower footing resistance value. Also, the rate of back-flashover has an effect on the value of the tower footing resistance by considering the number of electrode installations. A design is proposed for the grounding system of the tower footings in order to reduce the rate of back-flashover. The results presenting in numerical simulation indicates that it works properly after adding 4 electrodes. That is to say, installing 4 electrodes in each tower has successfully decreased the tower footing resistance value, back-flashovers rate 80% and 90-95% of present value respectively. The insulator voltage can be reduced to less than half of the present voltages as much as 30-50%. In more detail, in tower 77, the value of the tower footing resistance drops to 2.84 Ω, the flashover rate drops to 0.57/100 km/year and the insulator voltage drops to 0.99 MV when a disturbance occurs

EMTP model of a bidirectional cascaded multilevel solid state transformer for distribution system studies

This paper presents a time-domain model of a MV/LV bidirectional solid state transformer (SST). A multilevel converter configuration of the SST MV side is obtained by cascading a single-phase cell made of the series connection of an H bridge and a dual active bridge (dc-dc converter); the aim is to configure a realistic SST design suitable for MV levels. A three-phase four-wire converter has been used for the LV side, allowing the connection of both load/generation. The SST model, including the corresponding controllers, has been built and encapsulated as a custom-made model in the ATP version of the EMTP for application in distribution system studies. Several case studies have been carried out in order to evaluate the behavior of the proposed SST design under different operating conditions and check its impact on power qualityPostprint (published version

An EMTP Extension for Computing Earthing System Transient Step and Touch Voltages

This paper presents a novel technique for computing dangerous voltages due to lightning transients imposed on earthing system, which is based on the use of the well-known ATP-EMTP software package. Earth surface transient potential distributions, as well as step and touch voltages computations, are performed through extending the widely used EMTP software package with a new post-processor (computer program), developed especially for that purpose. The earthing grid is approximated by the circular cross-section conductors. In numerical model, conductors are subdivided into segments (1D finite elements) and Clark\u27s model with distributed constant parameters is then applied. Leakage conductance of conductor segments is modeled in EMTP as an additional lumped parameter. Analytical expressions for distributed and lumped segment parameters are derived using the average potential method. Due to the limitations of the EMTP, EM coupling between segments is neglected. The earth model is limited to the homogenous earth. Soil ionization effect is not accounted for, but could be incorporated, through some modifications of algorithms. Lightning surge model used is based on the Heidler\u27s model of current source

The lightning transient behaviour of a driven rod earth electrode in multi-layer soil

Kenneth John Nixon, Student no: 9307628H, PhD thesis, Electrical & Information Engineering, Faculty: Engineering & the Built Environment. 2006.The work presented extends and contributes to research in earthing and lightning protection and focuses on the transient behaviour of a driven rod earth electrode. Although previous work in this area has produced practical guidelines and models that may be used for lightning protection system design and analysis purposes, there has not been an investigation into the commonly encountered scenario of multiple layers of di erent soil types, particularly where high current densities cause ionisation to occur in the surrounding soil. In the research presented, the behaviour of a practical driven rod earth electrode subjected to peak impulse currents of up to 30 KA is analysed. Measurements obtained using a large-scale experiment arrangement are compared against results obtained using a time-domain circuit model simulation. It is shown that a single apparent resistivity value calculated from the steady state resistance equation and the measured steady state resistance can be used as a simpli cation for modelling the lightning current transient behaviour of a driven rod earth electrode in multi-layer soil. This represents a unique and valuable contribution to engineers working in the eld of earthing and lightning protection

Transient based earth fault location in 110 kV subtransmission networks

This thesis deals with ground fault location in subtransmission networks. The main subject of the thesis is transient based ground fault location using low frequency fault generated transients. However, the thesis also considers the conventional fault location methods and reviews the various other methods. Low frequency transient based methods, in general, are more precise and more reliable than the conventional methods based on fundamental frequency. They also avoid the need for further investment in existing systems that would be required, for example, for the implementation of travelling wave fault location, as existing transient recorders can be used. As a byproduct of the thorough investigation of conventional fault location and the presentation of its properties and limitations, a new error estimation technique is proposed. Fault generated transients are presented and tested, and their potential to aid fault location using the phase or neutral current is studied. The thesis also tries to solve some of the problems related to fault transient generation and propagation, as well as measurements and signal processing. The network configuration and transformer neutral grounding type receive special attention. The thesis shows the network conditions under which the method works reliably and accurately, and for critical conditions it proposes appropriate correction factors. The studies are performed for the 110 kV overhead lines under the jurisdiction of Fingrid (the Finnish electricity transmission system operator) for all kinds of neutral configurations. The EMTP/ATP software package is used as the network simulator. The results of the simulations as well as real ground fault recordings are analysed and processed in a fault locator developed by the author and implemented in Matlab.reviewe