Protective relaying system is a very complicated system, as it consists of one or more protective equipments, instrument transformers, wiring, tripping circuits, auxiliary supplys and communication systems. Therefore, it is necessary to take appropiate measures not to cause any weak points in the system for the practical use. This paper presents the appreciation of the manner to preserve the reliability and security of the system. Concrete measures to improve them are also described, which have been studied based on the experiences, and used in practical systems.
Recently, it becomes more difficult to build new generation plants close to the load center. It may produce a severe problem on the voltage stability of power system. On the other hand, it is expected that the introduction of the superconducting magnetic energy storage equipments (SMES) causes the improvement of the operation efficiency of the power system. It has been studied that SMES may be effective as a power system stabilizer. In this paper, the effect of SMES on the power system voltage stability is evaluated. Several control schemes are studied in order to improve the voltage stability. It is illustrated that, SMES being installed at the load bus, the voltage stability can be improved by the continuous control of the reactive power. Further, with the ability to control the real power, SMES can expand the operation limit. The optimum location of the SMES with respect to the voltage stability is also studied.
Control and protection of equipment in power systems generally require a high information processing capability to cope with today's power system requirements. Then, new digital control and protection equipment have been developed using high-speed and high-precision processors. Essential requirements for the new control and protection equipment are a multiprocessor architecture of distributed functions to retain sufficient computing power (fast and high-precision operations), and flexible and expandable hardware with high reliability. In multiprocessor architecture, it is important to determine how the distributed processors share the functions. By analysis and synthesis of relaying and control processings, we divided them into six processing circuits. This paper proposes a multiprocessor architecture of distributed functions, and using 32-bit floating-point and 16-bit microprocessors depending on the computational requirements. In addition a digital filter for fast sampled data is described along with performance of a digital relay.
The flow of fault currents in bundled conductors induces an electromagnetic attraction between subconductors thereby the bus conductor system to an extremely high level of tension. This tention, which is the most important factor in designing the mechanical strength of the system, is determined by a large number of parameters-the magnitude of the fault current, the size and number of the subconductors, spacer interval, the spring of the structure, and so on. Full-scale 63 kA-class fault current tests were carried out on eight types of bus conductor used in 275 and 500kV subconductors, and measurements of fluctuation in tension were used to clarify the relationship between the various parameters and maximum tension at fault time. A method was also devised for calculating maximum tension at fault time on the basis of the various parameters, and it has been applied in the mechanical strength design of bus conductor system.
Calculation of vertical and horizontal electric field waveforms over perfectly conducting ground, associated with tilted lightning strokes, is performed by decomposing a lightning channel into numerous dipoles. It is pointed out that waveforms are greatly affected by three-dimensional inclination of the lightning channel. Lightning-induced voltages on an overhead wire over perfectly conducting ground, associated with tilted lightning strokes, are calculated based on the equivalent circuit incorporating the horizontal electric field. The accuracy is ensured by comparison with experimental results obtained by a scale model. It is clarified that the tilt of the lightning channel greatly affects the lightning-induced voltage on a distribution line.
The authors newly develop a two-dimensional time-dependent simulation code considering the boundary layer for nonequilibrium disk MHD generator. In the code, the two-dimensional distributions of gas dynamical and electrical quantities in all over the generator on the plane including the boundary layer are calculated time-dependently without classifying the flow into the main flow and the boundary layer. In this paper, at first, the numerical procedure of the code is briefly explained. Next, calculations are performed using the two-dimensional simulation code for the same conditions as used in the experiments and the calculation results are compared with the experimental results and the quasi-one-dimensional time-dependent calculation results in which the displacement thickness of the boundary layer is assumed. As a result, the validity of the two-dimensional simulation code is made clear from the fact that the two-dimensional calculation results agree well with the experimental results. It is also made clear that the quasi-one-dimensional simulation code is not sufficient and the two-dimensional simulation code is required to calculate the performance characteristics of the generator in detail.
Quick response excitation type superconducting generators which are recently being developed have suprerconductors in the magnetic field windings. In those generators, the current of the magnetic field have to be controlled by extremely high speed. Therefore, high speed surge voltages are applied to the superconducting magnetic field windings. Surge characteristics for the transformers of normal temperature are well studied and reported up until now, but we can hardly find out the reports about the superconducting field windings. Consequently we are unable to apply the research results of the normal temperature conductors to the superconducting magnets by various reasons. This report shows the analysis, theoretical considerations and the results of experiments of the voltage distribution when the high speed surge voltages are applied to the superconducting magnet.
Two CO2-recovering cogeneration systems S-A and S-B are proposed for district heating and cooling which emit no pollutants such as NOx and SOx: S-A is a system constructed on the base of a closed dual fluid gas turbine cogeneration system and S-B a closed combined-cycle cogeneration system, both being able to be realized by combining conventional technologies. It has been estimated from the simulation results that the maximum net power generation efficiency of S-A and S-B is 31.9% and 35.3%, the maximum net heat generation efficiency is 62.7% and 35.7%, respectively. It was shown that S-A and S-B can reduce the amount of CO2 emission by 95.7% and 96.0%, respectively, compared with the case where electric and heat energy are separately supplied by using the conventional systems, although the fuel comsumption rate are 7.12% and 12.4% high, respectively. It was also shown that S-A and S-B can save fuel comsumption by 16.9% and 9.92%, respectively, compared with the case where the CO2 generated is removed and recovered from the stack gas in the conventional systems by using a chemical solvent.
Degradation of the global environment is one of the most crucial issues in the energy field. In particular, the global warming is a serious problem because the carbon dioxide produced by burning fossil fuels is a dominant source of anthropogenic greenhouse gas emissions. We need to develop technologies of controling CO2 emissions to mitigate the global warming. This paper presents a novel system of removing CO2 efficiently from power stations. We focus the research on the coal gasification combined cycle plant, and propose the system in which CO2 is removed from the fuel gas utilizing the shift reaction before the gas is burnt to generate electricity. We have computed thermal efficiencies in the following two types of combined cycle plants. One is the plant in which CO2 is removed from the fuel gas before the gas is burnt. The other is the plant in which CO2 is removed from the stack gas after the gas is burnt. Computed results show that the efficiency is higher by 2.6 percentage points in the plant of removal before burning than in the plant of removal after burning.