The air-termination system and the earth-termination system are principal components of an external lightning protection system connected by a down-conductor system, though they are physically quite different and are usually discussed independently. The physics of the air-termination system is less understood than that of grounding, and, as a result, various so-called nonconventional external lightning protection systems have been sold world-widely. In this article, the function of a conventional system is reviewed and performance of nonconventional systems is discussed.
This article reviews the effect of grounding resistance upon lightning performance of overhead power distribution lines (OPDLs). Good performance of lightning protection can be got by lower grounding resistance of OPDLs with surge arresters only. On the other hand the value of grounding resistance is not important for lightning protection for OPDLs with surge arresters and an overhead ground wire. Flashover in insulators does not occur by grounding potential rise but overvoltages in an insulator itself.
There has been increasing attention to how grounding systems should be implemented in the highly reliable ICT (information and communication technology) and power networks in the home and buildings. Recent buildings are required lightning protection measure with grounding systems to protect electric appliances, electronic devices, and communications equipment. At the same time, grounding system is having a growing adverse effect on EMC (electromagnetic compatibility). Considering these recent trends, this paper describes an integrated grounding system for homes and buildings that provides a safe, secure, and reliable operating environment for electric and electronic equipment and ICT equipment against lightning damage and EMC problems.
A reduction method of a lightning overvoltage on a Power Conditioning System (PCS) is investigated in this paper. The capacitors installed between the circuit and grounding terminal in the PCS determine the response against a first transient. The inductances, winding capacitances and excitation losses of the coils for the filter in the PCS should be also considered for estimating the overvoltage to ground at an input terminal of the PCS. The dominant factors of the maximum overvoltage are a grounding resistance, capacitances between a frame and output terminal of a solar panel and those between the PCS and ground. The overvoltage is decreased with decreasing the grounding resistance of the structure for the solar panels. The grounding resistance of the PCS has a minor effect on the overvoltage. The overvoltage can be reduced when a common grounding method is applied. A length of a cable between the output terminal of the solar panel and the input terminal of the PCS should be as short as possible.
The surge characteristics of a grounding conductor are quite different from those of an overhead wire. It is difficult to represent the characteristics of a grounding conductor in time domain without numerical simulation. This paper describes approximate formulas for voltage and current in a horizontal grounding conductor. The formulas are derived in time domain on the basis of the lattice diagram method, and are very simple. It is convenient from the engineer's point of view to do rough estimation of surge characteristics of a grounding conductor by the approximate formulas. Some empirical laws on the grounding have been employed without any discussions. The surge characteristics of a grounding conductor are discussed using the approximate formulas.
When a lightning strikes a building, potential difference may occur between different class grounding electrodes. Due to the potential difference, electrical equipment inside the building might break down or malfunction. Therefore, it is important to estimate the level of lightning overvoltage as accurately as possible and establish protection methodologies. In this paper, lightning overvoltage between grounding of a building and an individual grounding is discussed by experiments using a 1/10 reduced-scale model and the FDTD (Finite Difference Time Domain) method.
The outline of countermeasures which have been invested since 2009 to enhance lightning-proof characteristics of traction power supply system in Tokyo metropolitan area is summarized in this paper. The three major countermeasures are as follows: making grounding conductor length short, reduction of grounding resistance of substation mesh and introduction of permanent grounding electrodes for grounding resistivity measurement. The effects of each countermeasure based on the measured data are also shown.
A boat made of fiber reinforced plastic (FRP) is heavily damaged by a lightning strike. When the boat without any protection is struck by a lightning, not only the boat but also the crew on the boat may be damaged. Although it has been known that the importance of the lightning protection, information on the lightning damage is insufficient. It is necessary to clarify the invasion route of the lightning for an effective lightning protection, at first. Insurances had been paid on 94 cases for the lightning damages in FY 2011. Its total amount is about 84 million yen. The survey in this paper clarified that the small FRP boats are likely to be damaged by a lightning compared with ships. In many cases, a conductor located at a high position, such as an antenna or a rib of a tent of a fishing boat, was struck by a lightning. As a result, onboard electronic instruments were damaged. A reproductive experiment is carried out to reproduce a destruction of an antenna. From the result, it is cleared that a high voltage is generated across a loading coil of a radio antenna by a steep lightning current. The high voltage is determined by the inductance of the coil and the slope of the lightning current. The destruction mechanism of antenna that mounted on boat in the report was clarified by this experimental result.
A number of offshore wind farms are being in operation in the world. It is important to evaluate the characteristics of losses and output power of a large scale wind generation system like an offshore wind farm. This technical note presents analyses about the output power and loss characteristics of an offshore wind farm composed of permanent magnet synchronous generators (PMSG), power converters, and high voltage transmission cables connected to the onshore grid, in which two types of transmission systems, that is, HVAC and HVDC systems, are considered. Comparative analysis between the wind farms with two transmission systems is performed about annual output energy, system losses, and capacity factor for some typical regions whose wind speed data are expressed by the probability density distribution function obtained from Local Area Wind Energy Prediction System (LAWEPS) in NEDO homepage in Japan.
High growth in electricity demand during the period of Japan's bubble economy resulted in the construction of many power transmission facilities, including some loop systems. In some loop systems, there is a possibility of considerable power flow differences between heavy and light loads. Significant changes in the power system, such as from damage due to a natural disaster, would likely result in even larger differences and ineffective use of the loop system. Phase shifting transformers (PSTs) are highly efficient equipment for solving such power flow problems and some studies of operation methods using active power flow sensitivity have been carried out. Calculating active power flow sensitivity, however, requires using the DC method. Since doing so requires the fulfillment of several assumptions, errors may appear in the calculation results. This paper assumes protracted significant local loss of generation capability (about 20% of total capacity), and examines the resulting load changes in the loop system. We then propose use of PSTs to alleviate load differences among transmission lines, allowing more effective use of the loop system. Specifically, we propose the concept of active power flow sensitivity (APFS) and active power flow sensitivity 2 (APFS2). Installing PSTs at optimal locations and operating the PSTs with proper phase angles determined by a branch and bound method, we mitigate loading differences between heavily and lightly loaded transmission lines. The validity of the proposed method is confirmed by using a modified IEEJ EAST 30 model.
Since an output of Photovoltaic generation (PV) depends on weather conditions, it is concerned that the introduction of a large amount of PVs causes voltage fluctuation in power system. For this reason, in recent years, many investigations on voltage issues in distribution systems have been reported. Most of them assume that primary voltage of a distribution substation is constant under the condition that the primary voltage is properly managed using several facilities in transmission system. However, when a large amount of PVs is introduced in the distribution system, it is expected that the primary voltage of the distribution substation largely fluctuates and hence voltage fluctuation significantly occurs in the upper transmission system. Therefore, it is necessary to analyze in detail how much the introduction of PVs in distribution systems influences the voltage fluctuation in the transmission system. In this paper, a power system model in which both transmission and distribution systems are included is proposed, and the voltage fluctuation in the transmission system is analyzed in case that a large amount of PVs is connected into the distribution systems. Moreover, a reactive power control method is proposed in order to reduce the voltage fluctuation in the transmission system using Static Var Compensator (SVC) installed in the primary side of the transformer at the distribution substation. The effectiveness of proposed method is verified using some numerical simulations.
Transient stability analysis plays an important role concerned with the ability of power systems to reach steady state following large disturbances. Today's power systems are operated in significantly stressed state close to their limits. Fast determination of the system response is a crucial issue which raises the need for online stability assessment. Direct methods appear to be key approach to this problem of the power system transient stability analysis. A new robust method for detecting Controlling Unstable Equilibrium Point (CUEP) is proposed in this paper. The solution is obtained on basis of a minimization problem. The critical trajectory method (CTrj), another our approach, is applied to the Boundary of stability region based Controlling UEP (BCU) method. The method is combined with new criterion characterized by the potential energy boundary surface (PEBS) property. Starting from an exit point the method computes simultaneously multiple points of a trajectory that reaches CUEP. The effectiveness of the method is demonstrated through six power system models.
Using lithium-ion batteries that have higher energy density than lead-acid batteries, we assembled on electric bus and tested it as a base vehicle. The nominal voltage and nominal capacity of the battery packs are 365V and 120Ah, respectively. 15Ah lithium-ion battery, composed of 2 cells in parallel and 96 of pairs of what connected in 4 parallel, was applied to the bus. The bus was demonstrated over one year. In this paper, the characteristics of the 120Ah lithium-ion battery, the specifications of the bus system and field-test results are described.
The technique of analyzing the gases dissolved in insulating oil has been widely used to degradation diagnosis of oil-filled equipment such as transformers. On the other hand, oil-filled bushings can not be getting oil because power cut is required. In our study, we found that there are characteristics in frequency components of the electromagnetic wave radiated by partial discharge in oil. By using this characteristic, we have developed a method that can diagnose equipment in hot-line condition. However the cause of the characteristics has not been understood physically. Electromagnetic wave due to partial discharge is caused by the discharge current. It is expected that pulse waveform of current is steep if the velocity of charge is high, but waveform is gentle if the velocity is low. It is also expected that frequency of the electromagnetic wave is higher if the pulse waveform become steeper. Further, the moving velocity of the charge depends on the field strength. In addition, the strength of breakdown electric field depends on the insulating material. Then we forecast characteristic frequency components of partial discharge are affected by the difference of the electric field strength. So we tested the relationship between the rise time of the discharge current and the electric field strength. As a result, we confirmed that the discharge current waveform becomes steep due to the higher field strength. In this paper, we report the test result and developed method. And more, we introduce the examples of diagnostic result in field.
In some electrical installations equipped with the pressure relief mechanism for the internal arcing fault, metal grids are set up at the releasing parts. So it is necessary to understand how the pressure in such electrical installations rises during the internal arcing fault. This paper describes an investigation of the internal pressure rise due to the high current arc in an open chamber with releasing through a metal grid. In this investigation, we focused on both the peak value Ppeak and the time to peak tpeak on the internal pressure rise waveform where the oscillating component was removed, because it was experimentally observed that the general variation of such internal pressure rise with time had a point of turning from growing to lessening during the arcing. In order to investigate such internal pressure rise, a simple model for calculation was constructed, and was validated by a comparison with data from the experiment using a perforated metal plate as a metal grid. As a result of the investigation applying this simple model, the dependence of both the Ppeak and the tpeak on conditions of the metal grid, the chamber volume, and the arc energy was derived quantitatively.
Surge arresters and distribution equipments with zinc-oxide (ZnO) elements are used for lightning protection of overhead power distribution lines in Japan. The increase of surge arresters including distribution equipments with ZnO elements has resulted in a remarkable decrease of lightning outages of distribution lines due to sparkover. On the other hand, these surge arresters are sometimes damaged by direct lightning strokes, especially in winter. Winter lightning strokes have very large electric charge as compared with summer lightning strokes. For improvement of surge arresters, we have measured the energy absorption capability of surge arresters using natural winter lighting strokes to a test tower. The energy absorption capability of an insulator with built-in ZnO elements is about 1.4 times larger than that of a surge arrester with the same ZnO elements. The ZnO elements of the insulator are wrapped in an insulation sheet in order to fix ZnO elements in the center of the porcelain housing because the insulators are installed horizontally. The insulation sheet strengthens insulation of the side of ZnO elements, and the energy absorption capability of the insulator improves. The result indicates that wrapping ZnO elements in the insulation sheet is one of effective countermeasures against surge arrester failures.