A 66kV network is generally grounded through a neutral grounding resistor. In this network a single phase ground-fault current is limited to as small as 100_??_400 A. There are parallel four-circuit transmission lines mounted on the same tower in the 66kV network. In such transmission lines, the load and the fault currents could induce circulating current which flows through the lines. As the circulating current has zero-phase-sequence and negative-phase-sequence components, it could cause an unwanted operation of a balance ground relay using zero-phase-sequence current. However, it is difficult to compensate for the circulating current by the conventional vector compensation scheme. This paper has presented a new balance ground relaying to deal with the circulating current. In the relay from the ground-fault inception until the first tripping, the difference current Δ3I2d of negative-phase-sequence current 3I2d of the differential current between two protected lines is used as an input current. The Δ3I2d is the difference current of 3I2d between before and during faults. After the first tripping, the difference current of positive-phase-sequence load current and zerophase-sequence current of the above differential current are used as an input current. Consequently a higher sensitivity of the ground-fault protection for the above lines has been achieved. The correct operation of the new balance ground relay has confirmed when a single-phase-ground-fault occurred in the parallel four-circuit transmission lines, to which the relay is applied.
Electrohydro dynamics (EHD) is a new field which combines electricity, magnetism and hydro dynamics. EHD power generation is an application of this field. The author has conducted variational and maximum principle analyses of the optimal conversion process of incompressible EHD generation. However, a guiding principle in order to increase the output power and the physical meaning of the optimal conversion process have not been clarified sufficiently. In this paper, the simple optimal solution derived earlier from the maximum principle has made it possible to analyze the power conversion process from fluid energy to electric energy in detail. The optimal power conversion characteristics of incompressible EHD power generator are expressed in terms of slip. The conclusions of this investigation are summarized as follows: (1) The duct configuration becomes slender trumpet-shaped as the output power increases if the total duct volume is fixed. (2) The energy of working fluid pressure is converted to electrical and mechanical kinetic energies in the first half of the optimal process. Around the duct outlet, both the current density and the electric field intensity are decreased rapidly and the electric output energy density is reduced considerably. As a result, the kinetic energy is not fully converted to electrical energy but converted to energy of working fluid pressure. This is the basic principle to improve the conversion efficiency limiting the pressure drop between the entry and exit ends.
In a ground wire associated with an overhead transmission line, 5_??_10% of the current in a phase conductor usually flows due to the magnetic induction effect, and it brings some amount of power loss. In this paper, we propose a new reduction method of power loss in the ground wire. The current induced in the ground wire is effectively reduced by sectionalization of the ground wire every around 1 km along the power line. Thus, the total power loss also decreases so much. A computer program was developed in this process to calculate the exact current distribution in each section of the ground wire. We carried out field test on two different transmission lines in service to verify actual reduction of power loss by the proposed method. The ground wires were sectionalized prior to the test. The total power loss produced in the sectionalized ground wires were reduced to about one tenth in the original conventional arrangement. The observed current distribution agreed well with those estimated by the developed program. The sectionalized ground wire is grounded through all towers included in each section and, thus, the electrostatic shield effect to avoid lightning stroke to the conductors is never lost. The electromagnetic shield effect for adjacent communication lines is also effective. Finally it is shown from economical viewpoint that the saved kWh-cost due to the proposed sectionalization of the ground wire is much higher than the cost to realize the necessary improvement on the ground wire arrangement.
Installation of insulated wires in a high voltage overhead distribution system has decreased electric shock accidents, but on the other hand the ocurrence of wire melting accidents due to induced lightning surge has raised another problem. As flashover due to lightning surge takes place over the surface of insulator, leader strokes progress from the tip of the binding wire along the surface of the insulated wire. Clarifying the characteristics of these leader strokes will conceivably contribute to the prevention of wire melting accidents. Numerous experiments concerning these leader strokes were carried out, which resulted in clarification of several noticeable characteristics. From the results of this paper the following matters are clarified. (1) The progression speed of the leader strokes from the tip of the binding wire to the distance of approx. 20 cm along the surface of the insulated wire becomes faster with increasing gap (B G) length. (2) The potential of the tip of leader stroke against ground increases monotonously with the progression length, i. e. the distance from the tip of the binding wire. In addition, within the range of about 60 cm from the tip of the binding wire, the rate of voltage drop is approx. 250 V/cm. (3) The results of the measurement of the potential of the leader stroke tips against conductors at the moment of progression halt (progression halt voltage) carried out with respect to three sorts of insulated wires show that the progression halt voltage is dependent to sheath thickness and dielectric constant, and takes a constant value inherent to the insulated wire.
In this paper, it is discussed regarding influences of variable pitch blade to the starting and running characteristics of Wells Turbine with variable pitch blades. Taking notice of Wells Turbine with variable pitch blades, which is expected to improve the starting and running characteristics, we studied effects of variable pitch blade against to starting and running characteristics by means of numerical calculation. Numerical calculation was made by repetitive calculation including time transition from 0 s to steady running condition, using the formulas arranged. As the result of numerical calculation, the followings were confirmed that as the blade angle grows larger; (1) Starting Torque becomes larger, (2) it becomes easier to make self-starting, (3) it becomes easier to make cut-in-starting, (4) starting time becomes shorter, (5) turbine efficiency becomes higher, and (6) output becomes larger compared with fixed angle one. Conclusively, through this study, it was confirmed that Wells Turbine with variable pitch blade is effective for getting the better starting and running characteristics, further, shall be put into practical service, if proper design shall be made eliminating the remaind problems.