Many new technologies will be required in deregulated power systems. They are classified into three types: power system optimization techniques, reliability and ancillary service, and new techniques for analysis, operation, and control. Examples of individual technologies are: risk management, transmission expansion planning, security assessment, costing of ancillary service, wide area network data acquisition, fast analysis method, etc. Let us develop new technologies and open new era of power system.

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This paper describes a method to obtain a point for the shortest distance between a normal operation and a critical point of load flow in electrical power systems by means of Monte Carlo simulation. It also presents characteristics of power distance, voltage distance, and inner products of eigenvectors and voltage difference with respect to the point on the trajectory of minimum search. The critical point is characterized by the zero determinant of Jacobian matrix. The point is known as saddle node bifurcation. We propose a method to calculate the critical point under bus constraints of the load flow equation. A new set of voltages is give by random generator for a step of Monte Carlo simulation. We calculate the power distances and draw a trajectory for the closest bifurcation by the random process. The result shows that the right eigenvector is parallel to the normal line of tangential planes at the closest bifurcation.

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In a power system, the auto-reclosing schemes are applied in order to enhance the transient stability. However, conventional auto-reclosing techniques adopt fixed time interval reclosing, that is, the circuit breakers reclose after a prescribed dead time. Since the transient stability is dependent on the generator state of reclosing instance, this method may cause an unstable state when unsuccessful reclosing occurs. Therefore, the method to determine the optimal reclosing time is needed in order to enhance the transient stability of power system effectively.This paper proposes the method to determine an optimal reclosing time by using the kinetic energy of synchronous generators. The significance of this method is that it uses the kinetic energy of each generator which can be obtained easily. Consequently, this technique may be implemented for the on-line application. The proposed method is verified by simulation study using EMTP/ATP.

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This paper presents a new method to design -xed-structure robust controllers for enhancing stability of power systems. In a robust controller design without structural constraints, a high-order robust controller can be obtained by solving a convex optimization problem. However, it is difficult to implement the high order controller in existing control devices such as SVC and PSS. Since a robust controller design problem with structural constraints can be formulated as a BMI problem, we give a successive approximation algorithm,

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To cope with restructuring of electricity market, application of 22kV distribution systems to areas with high load density, is promising. To expand them, it is important to install 22kV distribution equipment on pavements and lots without fences. On the other hand, the neutral grounding method is expected for the 22kV distribution equipment in terms of rationalization of insulation. In this case, one line-to-ground fault current will be large. Therefore, to make safety of people, it is essential to decrease the contact voltage.
In this paper, we will perform the simulation of current distribution in the case of one line-to-ground fault and study the security of human from the viewpoint of both step voltage and contact voltage. We will also clarify that we can lower the contact voltage by grounding mutually insulated inner box and outer box separately. Then we will propose the improved grounding method.

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In our country, the peak demand load is increasing and the load factor of utility is decreasing year after year. However constructing the new power plant is not easy from the restrictions in respect of environment. Consequently operation of electric power systems is becoming more difficult. In order to solve this problem, introducing the LLS using photovoltaic (PV) power generation system or battery (BT) storage system is examined by the utility side. Since neither PV nor BT has the restrictions in respect of environment, it can be installed also in a city area. On the other hand, since a contract electric power can be reduced, introducing the LLS is advantageous also for a customer. However the system, characteristics and effect of LLS is not clear.
This paper deals with the operational benefit of LLS with solar cell and storage battery from customer side. The following became clear from the simulation results. 1) If the price of battery system reaches a target price, introducing the LLS becomes advantageous than introducing the PV system. 2) There is the best LLS corresponding to the electric power contract. 3) The operational benefit changes with the capacity of PV and BT.

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Concentration in population and business activities results in high energy demand in urban areas. This requires the construction of underground substations. Oil-less, non-flammable and non-explosive equipment is recommended for underground substations. Therefore, gas-insulated transformers have been developed. Development of the method for diagnosis of gas-insulated transformers is required.
In this paper, experimental survey over the main components of decomposes generated by various faults in gas-insulated transformers is described that is carried out through simplified model tests. These results will be used to develop the diagnostics method for gas-insulated transformers.

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It is well known that increasing conductor radius of grounding electrode results in decreasing grounding resistance, but the decrease extent is very little compared with the increase extent. However, when bundled conductors are used for grounding electrode, lower grounding resistance is expected to be obtained. Thus the bundled conductors of horizontal electrodes are better buried in full width of dug ditch (say, in 30cm width).
Of bundled conductor counterpoise and mesh electrodes in homogeneous and two-layers grounds, grounding resistances are computed, and compared with those of single conductor electrodes. It is shown that grounding resistances of bundled conductor electrodes are considerably less than those of single conductor. Furthermore, of counterpoise electrodes fed at one side, inductances and then impedances are computed. It is found that grounding impedances of bundled conductor electrodes are also considerably less than those of single conductor electrodes.

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The authors have conducted research to clarify the manner of lightning attachment on a power distribution line and nearby tree, in order to develop effective lightning protection measures. In the previous papers, discharge characteristics were examined by the application of impulse voltages to a rod electrode when an open wire on as an overhead ground wire was placed in the vicinity of a certain type of conifer tree. This time, we investigated how the sparkover status changes when applying a lightning impulse waveform to three kinds of trees: a conifer tree, a deciduous broadleaf tree, and an evergreen broadleaf tree. The results showed no significant difference in either the status or the rate of sparkover, regardless of the kind of tree. Further, we observed the sparkover status using a 3.5 m tree model composed of a sphere electrode and resistance, instead of a live tree, placed near an open wire. Through the experiment using the model, it was found that the equivalent resistance of a 3.5-meter live tree was in the range of 100kΩ to 200kΩ.

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To obtain instructions for performance improvement of planar solid oxide fuel cell, numerical simulations are performed for one channel region of its single cell. The two-dimensional time-dependent simulation code developed by the authors is used in the calculations. It is made clear that the single cell voltage of the counter-flow type cell is higher than that of the co-flow type cell, whereas adoption of the counter-flow type cell is not advisable because the cell temperature tends to become too high. The co-flow two-divided type cell with intermediate heat exchanger, which supplies heat required for fuel pre-reforming, is most advisable, because it provides almost the same single cell voltage with much less cell temperature rise in comparison with the counter-flow type cell. The single cell voltage at flrst shows an upward curve and next a downward curve as the inlet gas temperature becomes high, indicating that its optimum selection is also important for performance improvement.

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The use of renewable energies has been focused on for preserving environments and coping with the shortage of future energy supplies. In oceans, a tide reverses its current direction every six hours, and the current velocity changes into a sine wave after a period of time. Tidal current generation uses a generator to produce energy, changing the kinetic energy of current into a turning force by setting a water turbine in the tidal current. Therefore, it is considered to be very advantageous to use a water turbine that can always revolve in a fixed direction without any influence from tidal current directions. Water turbines with these characteristics are known as Darrieus water turbines. The Darrieus water turbines were modified for water from turbines originally developed for windmills. Darrieus water turbines have a difficulty in starting, but these days Darrieus water turbines have been developed with spiral blades, which make it easy to get the turbines started. However, there are very few reports regarding Darrieus water turbines with spiral blades, and therefore their characteristics are unknown. From the above points of view, this study devises and investigates spiral blade-Darrieus water turbines to clarify their characteristics through hydrographic experiments, and at the same time, it compares the characteristics of spiral-blade Darrieus water turbines with those of straight-blade ones.

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In high voltage aerial distribution systems, creeping discharges develop along the wire surface from the free end of the binding wire when overvoltages caused by the lightning surge invaded to the central line of an insulated wire. Then, the various disasters such as punch-through breakdown, disconnection and melting of wire, often occur at these systems. In our previous studies, it has been clarified that the lengths and aspects of creeping discharges under a 1.2/50μs impulse voltage condition can be affected remarkably by the change of the electric field intensity on the wire surface. However, the lightning impulse surges which may invade to a central line of wire have various values of duration of wave front. This will more complicate the creeping discharge phenomena due to a lightning.
In this paper, we report the influence of the duration of wave front both on the lengths and the aspects of the creeping discharges which develop on the wire under the application of lightning impulse voltages. It has been clarified that the behavior of negative creeping discharges reveals a remarkable change by the duration of wave fronts in the applied voltages.

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Side flashes often occur when lightning strikes a tree and cause injury or death of human beings staying nearby the tree. Necessary clearance to prevent the side flash has been said to be 2 m, but the physical meaning of the value is unclear.
In this paper, we have proposed a model of side flashes based on the physics of discharges and necessary clearance has been calculated. Furthermore, we have carried out model experiments of the side flash using real trees of a heights of 3.5 m and a naturally growing tree of a height of more than 10 m. The results of the model experiments have verified the proposed theory and it is concluded that clearance of more than 3 m from a tree is necessary to prevent side flashes from the tree.

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In the populated area, parallel running or crossing of AC and DC line may happen. Then there are needs of analyzing the interaction between AC and DC line for the better control and protection. For the demand, the interaction model has to provide capabilities to represent highly accurate DC initialization, dynamics in low frequency as well as higher frequency and excitations at specified frequency including resonance phenomena. This paper concerns the phase domain modeling and presents a modification of frequency characteristics in low frequency band for the accurate DC initialization, newly devised fitting techniques for the modified characteristics which use only real data, and an approximation method which makes the approximation error to be zero at the specific frequency. The examination of the phase domain interaction model constituted by these methods showed the high reliability in DC initialization and dynamic responses. Also the steady state outputs of the model following AC excitation agree well with those of the equivalent pi circuit.

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In standard simulations of short circuit faults in power systems, it is common to neglect transients of the transmission networks and armature circuits of generators. Therefore, it is not possible by standard method to evaluate particular phenomenon arised from the armature transient. It is well known that the standard method can not evaluate the backswing phenomenon caused by the armature transient. This paper applies a new method, which can approximate the DC offset currents that arise from the armature transient, to transient stability simulation of power system including wind generators.

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