This article introduces the survey results of fault location technique in power systems. The power transmission line Fault Locator (FL) is an indispensable device for early determination of fault location on power transmission line. Several types of FL have been developed to date, including the pulse radar type, surge type and impedance type. The purpose of this article are to pick up overview of FL of the three types. Furthermore this article introduces about applied FL in field and the research trend of FL.
It is difficult to assess how transient stability of trunk transmission power systems may be affected by a system fault under the conditions created by the widespread use of renewable energy (RE) because it may greatly differ depending on power system conditions such as the operation statuses of generators and RE, and also on whether or not any RE is tripped after the fault, for example. Then we developed photovoltaics (PV) generation model for transient stability analysis and defined a scenario for the widespread use of RE in order to perform an analysis using this power system model. We confirmed that this made it easy to identify the impacts on transient stability and their causes even when different power system conditions contribute in a complex manner.
In recent years, environmental problems have been becoming serious and wind power generation has attracted much attention and been introduced due to its less environmental impacts. Since wind power generation is an unstable power source in which its output fluctuates due to wind speed variations, wind power generator output needs to be smoothed when supplied to the power system. This paper proposes a control method to suppress the power system frequency fluctuations by attenuating wind power generator output of certain frequency band, which cannot be suppressed sufficiently by the conventional frequency control, through on-line spectral analysis of power system frequency deviation.
The number of Doubly Fed Induction Generator (DFIG)-based wind power generator is increasing because of its good efficiency and controllability. Power Oscillation Damping control for power system stabilization is expected to be implemented in the DFIG, and a few works have so far discussed it. This paper proposes a control parameter optimization method considering transient response to improve not only small signal stability but also transient stability. Moreover, to improve both transient and small signal stability, a combined control method with switching control is proposed. The effectiveness of proposed method is confirmed by eigenvalue analyses and time domain simulations.
This paper examines the influence of aggregated power output fluctuation of photovoltaic power generation system (PVS) on the power system frequency, focusing on ramp-events of aggregated PVS power output. A numerical simulation model of economic load dispatching control (EDC) and load- frequency control (LFC) is used together with a PVS power output forecasting model and a unit commitment (UC) scheduling model developed in our preceding study. As a result, in the case of ramp event with long duration and high ramp rate, the frequency violation occurs when the power output of controllable generators with high load following capability reaches to upper/lower limit even if the power output of low load following capability generators is still available. If the load dispatching scheme is tentatively changed from the conventional EDC using an equal incremental fuel cost rule to, for example, a dispatching policy based on the capacity without the consideration of fuel cost, the aggregated load-following capability can be kept, avoiding the frequency violation.
In recent years, the large amount of photovoltaic generation system (PV) is installed in the distribution system. However, violent voltage fluctuation caused by PV output will make it difficult to maintain the distribution line voltage within a proper range. Furthermore, the voltage imbalance that make difficult to control the line voltage is also severe problem. In order to overcome these problems, fast voltage control devices, such as Dynamic Voltage Regulator (DVR), STATic Synchronous COMpensator (STATCOM), and so on, are studied, however they have problem of expensive cost. From this background, Hybrid Voltage Regulator (HVR) which is composed of a small capacity converter and tap changing circuit by thyristor switches is proposed and fundamental control evaluation is presented in past paper. This paper proposes the control algorithm of HVR to suppress the voltage imbalance and to maintain the line voltage within a proper range. The proposed method is also evaluated by the simulation of a long line distribution model.
In a transmission line passing through a snow region, snow inevitably accretes on insulators more or less and partial discharge might occur on insulator strings covered with snow. Since partial discharge occurring at the surface of polymeric insulator may deteriorate the insulating property of it, it is necessary to find the magnitude of discharge current as well as the location or occurrence frequency of partial discharge to grasp the degree of degradation. The paper shows the method for estimating the magnitude of the discharge current from the images taken by an ultra violet camera. To simulate partial discharge occurring at an air gap in capped snow over an insulator, ac partial discharge was formed between a pair of ice electrodes or snow walls. By increasing applied voltage to the ice or snow electrodes, discharge current was increased. The luminous area in UV image was increased with the magnitude of discharge current below 10mA. The magnitude of discharge current flowing through an air gap formed in accreted snow can be estimated from the luminous area in UV image.
To develop an alternative test method for internal arc in SF6-insulated power equipment, we have systematically obtained experimental data on SF6 arc to calculate the pressure rise in power equipment. In this study, we carried out experiments on SF6 arc in a closed container. The arcs were ignited between rod electrodes by applying a current with a peak of 10.7kA and a duration of 40ms. The rod electrodes were made of copper, iron, and aluminum. It was found that the maximum pressure rise was highest in the case of the aluminum electrode. Additionally, to determine the energy balance resulting from a SF6 arc in the container, the energy balance was discussed on the basis of input energies and consumption energies. The input energy components are the arc energy and the energies of the decomposition reaction of SF6, the oxidation reaction of metal vapor, and the fluoridation reaction of metal vapor. On the other hand, the consumption energy components are the energy contributing to the internal pressure rise and the energies associated with the melting of electrodes, the vaporization of electrodes, and the radiation emitted from the SF6 arc. It was found that the input energies approximately agreed with the consumption energies. The energy of the fluoridation reaction of the metal vapor was highest in the case of the aluminum electrode, and the energy accounted for about 20% of the total input energy. Also, the radiation energy in the case of the aluminum electrode was comparable with that for the iron electrode, and the energy contributing to the internal pressure rise was highest in the case of the aluminum electrode.
In this paper, we present an analysis of the pressure rise caused by combusting of oil resulting from a fault arc, assuming that the arc occurs in oil-filled equipment in a large electric room with an opening. In the analysis, we clarified that the location and volume of the arc fault and the location of the opening affected the pressure rise and the propagation around the arc fault. We found that the initial pressure rise (P1st) at the floor adjacent to the wall and equipment was greater than those at other locations. In particular, P1st was largest at the corner of the electric room owing to a superimposed pressure wave. Moreover, the value ofP1st at the floor adjacent to the equipment was independent of the location of the opening. It was also found that P1st decreased inversely propositionally to the distance between the floor adjacent to the wall and equipment and the location where the fault occurred. Also, the time to reach P1st was decided by the distance in spite of part of arc fault, arc fault volume and location of the opening, and the pressure wave which occurs from the arc fault is propagated in air at sonic speed, The results would be utilized for a strength design of wall in an electric room.