kV Overhead Distribution Research Articles

Analysis of Induced Voltage of Optical Fiber Composite Ground Wire in 35 kV Overhead Distribution Lines

Analysis of Induced Voltage of Optical Fiber Composite Ground Wire in 35 kV Overhead Distribution Lines

Observation of induced voltage on 10 kV overhead distribution lines with and without shield wire by rocket triggered lightning

This article studies the performance of lightning-induced overvoltage (LIV) on a 1513 m overhead distribution line in the absence or presence of shield wire, via rocket-triggered lightning experiment. It's found that whether the shield wire is erected or not has little influence on the waveform characteristics of LIVs, but mainly affects the voltage amplitude. The shield wire primarily reduces the positive peak value of LIVs at the station closest to the lightning channel, but has little influence on the negative peak value. On the contrary, for the station farthest from the lightning channel, the shield wire mainly reduces the negative peak value of LIVs, but has little impact on the positive peak value. By using the ratio of the average values of the statistical data under the operating condition with or without shield wire, it's found that for peak-to-peak value measured at the closest station, the closer to the shield wire, the smaller the ratio is. The ratio of phase A is about 0.78, while the ratio of phase C is about 0.88. For the station farthest from the lightning channel, the ratio is about 0.95, and there is no obvious difference between three phases.

Influence of configuration of power distribution lines on failure probability of surge arresters

In Japan, many surge arresters have been installed on 6.6 kV overhead distribution lines for reducing lightning overvoltages. The increase of surge arresters has resulted in a remarkable decrease of lightning outages of distribution lines caused by insulator flashovers. In contrast, several surge arresters have been damaged by direct lightning strikes to distribution lines. Studies of countermeasures for the failure of surge arresters are generally carried out by lightning surge analysis using the Electro Magnetic Transients Program (EMTP). In the previous studies, a simple model of a straight line is used, however, branch lines and termination points also exist in the actual distribution lines. In this paper, we present the influence of configuration of distribution lines on the failure probability of surge arresters obtained by the lightning surge analysis.

Practical Schemes on Lightning Energy Suppression in Arresters for Transformers on 10 kV Overhead Distribution Lines

This paper presented an assessment of lightning energy absorption by dedicated surge arresters (SA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DT</sub> ), which are provided to protect the distribution transformers on 10kV overhead distribution lines (OHLs). A hybrid Partial Element Equivalent Circuit-Multi-conductor Transmission Line (PEEC-MTL) code was applied to evaluate lightning surges on SA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DT</sub> . This method has the capability of modeling both short and long wires in OHL systems and is verified numerically and experimentally. A Monte Carlo procedure was adopted to assess the fault rate (FR) of SA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DT</sub> . It is found that the direct lightning strokes to the phase wire are the primary threat to the SA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DT</sub> , compared with the strokes to the poles as well as indirect strokes to the ground or structure nearby. Several protection schemes are identified, and their performance is evaluated from the aspects of lightning protection and economic cost. The full shielding wire (SW) scheme performs the best, but with the most expensive protection cost. The lightning energy absorption by SA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DT</sub> can be suppressed significantly by installing extra SAs on the adjacent poles. The scheme of two or four extra SAs together with a partial SW can achieve a balanced performance of protection effect and economic cost for the OHL. The SW for a section of the OHL alone is not enough to the lightning protection for SA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DT</sub> .

Selection of parameters of overhead lines models when calculating transient processes during earth faults in 6–10 kV networks

Single phase-to-ground faults are the most common type of faults in 6–10 kV overhead distribution networks. Arc intermittent single phase-to-ground fault (PSP) are the most dangerous for the network and the damaged element. They are followed by intense transient processes and, as a result, dangerous overvoltage rate and significant transient current surges at the point of insulation damage. PSP transients also have a significant effect on the selectivity and operation stability of protection devices against this type of damage. Therefore, the development of the methods and means to improve the operation efficiency of 6–10 kV overhead networks in case of PSP and technical improvement of protection devices in many cases is due to the need to calculate the transient processes that occur during insulation breakdowns of the network phase to earth. For the systems under consideration, the reliability of transient processes calculations in case of PSP is determined mainly by the accuracy of estimation of the parameters of 6–10 kV overhead lines, first of all, of inductance, which generally depends on the frequency of the transient current components. In the scientific papers devoted to the study of transient processes in case of PSP in medium voltage electrical networks, including 6–10 kV overhead networks, constant (frequency independent) values of inductance are used as a rule in the equivalent circuits and in the models of transmission lines. An urgent task is to estimate errors caused by the application of this approach to determine the parameters of 6–10 kV overhead lines during the calculations and modeling of transient processes during PSP, and cases of its application. Advanced methods of modeling of electric power systems and their elements have been applied with the use of COMSOL Multiphysics and PSCAD software to obtain the frequency dependences of the inductances of a 6–10 kV three-phase overhead line and study of their influence on the calculation accuracy of transient currents and voltages in case of PSP. The parameters of 6–10 kV overhead line models developed in the indicated software packages at a frequency of 50 Hz are set in accordance with the reference data. The authors obtain the errors estimation to determine the parameters of transient currents and voltages during PSP in 6–10 kV overhead networks when using transmission line models. The frequency dependences of inductance, which are up to 40–50 % in amplitude are not considered. The results show that application of frequency-independent models is permissible only in the cases when parameters of the calculated equivalent circuit of the network and position of PSP point remain practically constant, when solving problems that require high accuracy to determine the parameters of transient currents and voltages, for example, to determine remotely the location of a ground fault, it is necessary to use frequency-dependent models of 6–10 kV overhead lines. Introduction of the developed recommendations to determine 6–10 kV three-phase overhead lines parameters allow us to increase the reliability of calculations and to avoid raw errors when solving the problems which are related to the study of transient processes in case of earth faults in the networks of the given voltage class.

Design Consideration of the Shielding Wire in 10 kV Overhead Distribution Lines Against Lightning-Induced Overvoltage

This paper presents a systematic investigation into the performance of a shielding wire on 10 kV overhead lines (OHLs) against indirect lightning, from the design point of view. The design parameters addressed include the grounding interval, grounding resistance, and position of the shielding wire. As a system outage is usually caused by insulator flashover at OHL poles under indirect lightning, the induced voltages there are investigated with the code developed from the Agrawal model. In the evaluation, the location of a lightning return stroke relative to a grounded or ungrounded pole is considered. It is found that the lightning channel positioned in the front of an ungrounded pole could completely wipe out the effect of the shielding wire. This occurs if the wave from the grounding point arrives later than the time to the peak of the voltage directly arising from the lightning return stroke. It is suggested providing the wire grounding at every pole even if the grounding resistance at some poles is much higher than the design value. Grounding spacing does not affect the induced voltages at the pole generally if the pole has been grounded. One critical parameter is identified, i.e., the distance between the shielding and outer phase wires. Minimizing the distance can effectively reduce the lightning-induced voltages.

Fault Location in 6.6kV Overhead Distribution System by Comparing TDR Waveforms Before and After Failure

The authors propose an effective method of fault location in overhead distribution system. In past studies, short pulse with high frequency injected into overhead distribution system can propagate through about 1km distance, but it has been a problem that pulse reflect at other than a fault point. In other words, it is necessary to find out a fault point from multiple reflected waves. In our proposed method, it is possible to extract a change of a fault point by comparing TDR (Time Domain Reflectometry) waveforms before and after failure. In this paper, we clarify theoretical concept and organize the algorithm of comparing TDR waveforms. Moreover we verify effectiveness of the proposed method by experiments in real-scale distribution system after confirming pulse transmission properties of section switch. The verification results show that the proposed method can locate a fault point (short-circuit fault or ground fault) with accuracy of tens of meters or less.

Economic Analysis for Replacement of 11kV overhead Koteshwor Feeder by Underground Distribution System

Cost effective, Aesthetic and Reliable energy supply is the need of any mankind. In this study, economic analysis for replacement of 11 kV overhead distribution feeder by 11kV underground cable is done with reference to Koteshwor Feeder under Baneshwor Distribution and Consumers Service. The reliability indices like SAIDI, SAIFI, ENS etc. is performed by using DigSilentPowerFactory software. The reliability of overhead distribution system is evaluated by using real system data system and similarly, historical IEEE standard data is used for underground distribution system. The reliability indices are compared for both distribution systems. Result shows that interruption in the overhead system is more than underground distribution system, the energy not supplied to the customer by overhead distribution system is also more than underground distribution system. The replacement cost estimation is performed by using Nepal Electricity Authority (NEA) unit rate and KEI industries quoted price for NEA underground project. The B/C ratio and Present Worth value for the 25-year period of useful life shows that the replacement of the existing overhead distribution system by underground distribution system is financial suitable and can be payback by revenue save from the Energy Not Supply (ENS) lower value of underground distribution system than overhead distribution system. In order to get the continuous of supply, esthetic and public safety in electricity distribution field one may have to bear initially extra cost to use underground distribution systems which finally get payback. Thus, in case of densely populated city like Kathmandu, underground distribution system is reasonable requirement for continuous supply, esthetic and public safety in electricity distribution filed.

Artificial neural-network-based fault location for power distribution lines using the frequency spectra of fault data

This study presents an artificial neural-network (ANN)-based digital fault classification and location algorithm for medium voltage (MV) overhead power distribution lines with load taps and embedded remote-end source. The algorithm utilizes frequency spectra of voltage and current samples which are recorded by the digital relay at the substation. In the algorithm, to extract useful information for ANN inputs, the frequency spectral analysis of voltage and current waveforms has been carried out using Fast Fourier Transform. To classify and locate the shunt faults on an MV distribution system, a multilayer perceptron neural network (MLPNN) with the standard back-propagation technique has been used. A 34.5 kV overhead distribution system has been simulated using MATLAB/Simulink, and the results are used to train and test the ANNs. The technique takes into account all the practical aspects of real distribution system, such as errors, originated from instrument transformers and interface. The ANN-based fault location technique has been extensively tested for a realistic model and gives satisfactory results for radial overhead distribution systems with load taps and in the presence of remote-end source connection.

Defining the practical constraints of inserting DG units in distribution systems regarding protection schemes

Summary This paper presents a general framework to determine the location and capacity limits of distributed generation (DG) in the distribution system (DS) in order to maintain the traditional protection scheme. The impacts of DG penetration on overcurrent protection coordination are analyzed including fuse–recloser and recloser–relay. The minimum boundary of DG penetration in distribution system and the effects of modifying the setting of overcurrent protective devices have been investigated. Applying this framework in the developing countries could save money and time during integration of DGs to the network on a large scale based on country regulation. The proposed framework is implemented on a typical 11 kV overhead distribution feeder using Matlab/Simulink® and Etap® simulation packages. Protective device coordination under different fault locations and types with and without the DG is investigated. The results show the possibility of minimizing network power losses and improving voltage profile without replacing the existing protection system. Copyright © 2015 John Wiley & Sons, Ltd.

Lightning Flashover Rates of Overhead Distribution Lines Applying EMTP and IEEE Std.1410

This paper calculates the lightning flashover rates of 22 kV overhead distribution line. In order to calculate the backflashover rate (BFOR), the performance of line which related to the insulator backflashover has been modeled and analyzed using Electromagnetic Transient Program (EMTP). The flashover models, volt time curve (VT), disruptive effect model (DE) and leader progression model (LPM) have been compared. The shielding failure flashover rate (SFFOR) and induced voltage flashover rate (IVFOR) have been calculated follow equations given in IEEE std 1410-2010. Finally the total numbers of flashovers of line have been determined. The lightning flashovers rates of BFOR, SFFOR and IVFOR have also been compared with the data taken from the line outages recorder. From the system being studied shown that, the total numbers of flashovers from simulation and calculation is closed to the data from the line outage recorder.

Lightning Performance on Overhead Distribution Lines : After Improvement Field Observation

Two feeders of 20 kV overhead distribution lines which are located in a high lightning density area are chosen to be observed as a field study due to their good lightning performance after improvement of lightning protection system. These two feeders used the new overhead ground wire and new line arrester equipped with lightning counter on the main lines. The significant reduced of lines outages are reported. Study was carried out to observe these improvements by comparing to the other two feeders line which are not improved and not equipped yet with the ground wire and line arrester. These two feeders located in the nearby area. Two cameras were installed to record the trajectory of the lightning strikes on the improved lines. Lightning peak currents are measured using magnetic tape measurement system installed on the grounding lead of lightning arrester. Lightning overvoltage calculations are carried out by using several scenarios based on observation results and historical lightning data derived from lightning detection network. Lightning overvoltages caused by indirect or direct strikes are analyzed to get the lightning performance of the lines. The best scenario was chosen and performance of the lines were improved significantly by installing overhead ground wire and improvement of lightning arrester installation.

Simulation of isolated operation in fault condition by loop power flow controller

6.6 kV overhead distribution systems are currently constructed in Japan as radial networks. The load imbalance of each feeder therefore has a negative impact on voltage stability. On the other hand, disconnecting distributed generators with faults causes line overload or under-voltage. Therefore, controlling line voltage and line power flow on the distribution system is critical for the open access of indefinite numbers of distributed generators. We are investigating a new loop or mesh structure distribution system to maximise network capacity. This paper describes a control method for a loop power flow controller (LPC) focusing on 1 line-to-ground (LG) fault states.

Efficient Operation Regions of Power Distribution Transformers

A new concept of efficient operation regions of distribution transformers on power factor versus active power (cos/spl phi/-P) plane is proposed. Based on it a visual analysis method is obtained to determine efficient ranges of operating transformers. This method could be used for analyzing efficiency of transformer loading based on databases of the distribution automation system, and the real-time operational loci of distribution transformers could also be obtained. An application of this method in a 10 kV overhead distribution automation system is given.

Simulation of Isolated Operation in Fault Condition by Loop Power Flow Controller

6.6kV overhead distribution systems are currently constructed in Japan as radial networks. The load imbalance of each feeder therefore has a negative impact on voltage stability. On the other hand, disconnecting distributed generators with faults causes line overload or under-voltage. Therefore, controlling line voltage and line power flow on the distribution system is critical for the free access of indefinite numbers of distributed generators. We are investigating a new loop or mesh structure distribution system to maximise network capacity. This paper describes a control method for an LPC focusing on 1LG fault states.

A Study on Insulation Level Decrease of 22 kV Overhead Distribution Line in Isolated Neutral System

For insulation design of 22 kV overhead distribution lines, major guidelines have been specified: (1) Have enough insulation ability against the line’s internal abnormal voltage, while arresters are used against external abnormal voltage such a lightning surge. (2) Decrease the line insulation level by using specific arresters capable of regulating the switching surge, resulting in an overall BIL decrease. The first specification is commonly adopted because the arrester’s absorption energy against the switching surge is not yet identified. The revised JEC testing voltage standard specified further lowered the insulation level (LIWV 100 kV), but its target was only for the 22 kV overhead distribution lines in a resistance grounded neutral system. Recently, focus is placed on studying for protecting the lines from direct lightning strikes, thus a variety of lightning protection equipment is widely applied on the lines. Consequently, guideline (2) above is also taken into account. In short, 22 kV overhead distribution lines will achieve both decreasing insulation level and improving lightning protection ability by installing many arresters for LIWV 100 kV in an isolated neutral system. Given these circumstances, to make this idea feasible, the authors studied the absorption energy of the proposed arresters against the internal abnormal voltage of the 22 kV overhead distribution lines in an isolated neutral system. The results revealed that the arresters are well applicable to the 22 kV overhead distribution lines.