Toshiya Ohtaka

CFD Calculation of Pressure Rise Due to Internal AC and DC Arcing in a Closed Container

Computational fluid dynamics calculation results of pressure rise and propagation due to high-current arcs in a closed container are described. The pressure developments at different locations within the container are calculated by changing the current frequency (ac of 50 and 60 Hz, and dc) and the electric arc energy input (up to approximately 1000 kJ). The local pressure oscillation amplitude for AC/50 Hz within the container exceeds that for dc. From the pressure oscillation period and the sound speed distribution in the container, the following conclusions are made. With growing electric arc energy, the pressure amplitude increases because of the resonance effect between the arc power oscillation and pressure waves reflected on the walls. When the electric arc energy reaches a value of around 500 kJ, the pressure amplitude rises significantly. This is considered attributable to superimposition of pressure waves near the container wall caused by low propagation velocity of the pressure waves near the wall. It is necessary to consider this phenomenon for public safety when designing electric power equipment.

Voltage stability preventive and emergency preventive control using VIPIt sensitivities

Recently, as power system loads are located farther away from power plants and are more unevenly distributed, reactive power losses have tended to increase due to the heavier power flow with high load growth and long distance transmission. Therefore, an effective voltage control scheme has been brought to attention in a considerable number of studies. Hence, We propose on-line voltage stability control schemes, i.e. a preventive control and an emergency preventive control, in addition to conventional local controls. In order to assess the effect on voltage stability in different generators, we propose the voltage instability proximity index including three power flow equations in a specified value space (VIPIt) based on the conventional index VIPI.

Development of an EMTP Simulation Model of Arcing Horns Interrupting Fault Current

Arcing horns interrupting fault current is a new type of arcing horns installed on transmission-line towers, which act to interrupt fault current independently within one cycle of commercial frequency. In this paper, we have developed an Electromagnetic Transients Program (EMTP) simulation model of the arcing horns interrupting fault current to ascertain the application effects and devise an installation strategy. The EMTP simulation model can consecutively simulate the entire process, from fault occurrence to fault clearing, by integrating two different kinds of macroscopic arc models, and is capable of dealing with the entire short-circuit current range by taking into account the characteristics of the arc parameters. Finally, we have verified the validity of the EMTP simulation model by comparing simulation and experimental waveforms, and have shown the simulation of current and voltage waveforms in the event of a system fault by using the Japanese Power System Model as an application example of the EMTP simulation model.

Power system stabilization using GPS and second-order eigenvalue sensitivity

As the electric power demand increases, power systems have become larger and more complex. The dependence on the electric power in society tends to increase such as information products prevail. On the other hand, studies on applications of Global Positioning System (GPS) to power systems monitoring are being conducted. In this paper, at first we propose a GPS placement method with a viewpoint of effectively monitoring the power system stability. This method uses the first order eigenvalue sensitivities for phase angles from relationship between eigenvalues and phase angles. Next, we propose a method for determining more appropriate generation dispatch rescheduling to improve the power system stability when the power system stability deceases. At that time we use first and second order eigenvalue sensitivities. The proposed method is demonstrated using a sample 4 machine 10 bus system and we examine effectiveness of the second order eigenvalue sensitivities compared with the first order ones.

Development of a Method of Calculating the Melting Characteristics of OPGW Strands Due to DC Arc Simulating Lightning Strike

Some strands of composite fiber-optic ground wire (OPGW) are sometimes melted and broken by high-energy lightning strikes. DC arc tests simulating lightning strikes have been performed to obtain the melting and breaking characteristics of OPGW strands. The tests have to be performed under many conditions concerning the arc (e.g., current, duration, polarity, gap length) and the OPGW (e.g., size, type, and number of strands) to clarify the melting and breaking characteristics of the strands. In this paper, the calculations regarding the melting characteristics of strands are performed considering the transferred heat and its area from the arc to the strands under the aforementioned conditions. The melting characteristics of strands are calculated with an arc current of 1-100 kA considering the measured current of actual lightning. The calculation results of the strand melting duration depending on arc current show good agreement with the experimental values obtained in dc arc tests.

Novel Arc Ignition Method Through Pre-Arc for Power Arc Tests

Metal ignition wires are widely used in power arc tests on insulator sets and similar. Finer metal ignition wire is preferred from the point of view of influence on the apparatus tested. However, if the metal ignition wire is too fine, the arc cannot be sustained. To perform a power arc test successfully, therefore, the metal ignition wire needs to have some degree of thickness. With these requirements in mind, we proposed a novel arc ignition method that allows the use of an extra fine wire by leading to the pre-arc in a current of several dozen amperes. In this paper, the sustainment characteristics of arc ignited from an extra fine copper wire using this novel method were investigated with a gap between the rod electrodes. The results showed that the kiloampere-class arc with a gap length of meter class could be ignited through pre-arc from the copper wire that is 0.03 mm in diameter with a voltage of 12 or 24 kV. The influence of the copper wire thickness on arc characteristics was also studied by comparing the arcs ignited by this novel method with those ignited by the general method where copper wires exceeding 0.3 mm in diameter were used.

A consideration on rate of reactive power service from generators in liberalized power market

The deregulation of the electric power industry has progressed in the world. It contributes to reducing electric rates, but there is possibility that the power system might become deteriorated. Under the circumstances, ancillary services that maintain system reliability and security become more important. There are various services in ancillary services, for example long-tern power reserves, power/frequency control, voltage/reactive power control and so on. In these services, it becomes a subject of discussion on how to procure and receive the services and how to pay money for the cost of the supply of ancillary services. In this paper, we focus our attention on reactive power supply of ancillary services. Then, we propose a calculation method for the rates based on an improved nodal pricing, and consider rates of reactive power supply service from generators.

Design of load frequency control based on /spl mu/-synthesis

In this paper, we propose a designing method of a load frequency control that is able to consider the change of operating points in the power system using /spl mu/-synthesis. We consider the change of the operating points as parameter variations in the inertia constant, the damping coefficient, and the synchronizing coefficient. As an example, we have designed a case for a three-area system, and run simulations for the system to compare the proposed method with a traditional method (PID type controller). As the results of the simulation, the validity of the proposed method has been confirmed.

Preventive control with RIDGE theory considering n-th swing stability

As the electric power demand increases, power systems become larger and more complex. To keep the reliability, preventive control is desired in power system operations. It is necessary to shift a system to a stable side beforehand using the preventive control, so that the system may be stable even for some disturbances. In this paper, we use RIDGE theory to judge the transient stability for the preventive control. The authors use the characteristics of RIDGE theory to judge transient stability, and the proposed method can judge the transient stability fast. Simulations are carried out using 3 machine 9 bus and 10 machine 47 bus systems to confirm the validity of the proposed method.

Optimal Placement of Facts From Dynamic Performance Viewpoint

Abstract UPFC which is one of the FACTS devices, can control transmission line reactances and ph~se angles. In this paper we propose a method for determining the optimal allocation of UPFC devices. In this method, for a multi-machine power system first through numerical simulations severe fault conditions are found. Then a UPFC device is allocated to different buses and behaviors of the control inputs under the severe fault conditions are studied. The less control effort for the system equipped with UPFC means the most efficient UPFC allocation. The effectiveness of the proposed method is shown using a four-machine eleven bus power system model.