To reduce boiler fuel cost, a new ELD method (economic load dispatching method) based on a dynamic fuel cost model, which is more accurate than the conventional quadratic model, is proposed First, ARMA model (Auto Regressive Moving Average model), which is a constant coefficient linear digital filter, is applied in order to supplement the quadratic model. We call the supplemented model ARMA-model-supplemented quadratic model. By using this model, the model deviations from actual data have been reduced Second, based on the ARMA-model-supplemented quaic model, we formulated the ELD problem into a quadratic programming problem, where the objective function is the summation of all units' fuel costs over multiple time points and the constraints are the supply-demand balances, the upper and lower generation limits, and the ramp rate limits. This problem can be solved by the standard quadratic programming technique. We call this new ELD method BEST method short for Boiler-dynamics-based Economic load diSpaTching method. Then, in order to make the problem size smaller, we propose a scheme to ignore all the time points except for the points corresponding to the peak, the bottom, and the steepest point on the forecasted load curve. We call this scheme sample scheme. Finally, the BEST method with the sample scheme are evaluated by numerical simulations on Kansai Electric Power Systems and it is shown that the proposed method can reduce the calculation time without compromising the fuel cost.
The dynamic behaviours of the TCUL controls are investigated from the viewpoint of the effect of control actions on voltage stability as well as on voltage regulations, taking into account the interference among the multiple control actions of TCULs. The Liapunov stability theorem is applied to a system having nonlinear voltage dependent loads to derive conditions for stability. We define the term “reverse control action for multiple TCULs” to indicate undesirable tap operations, where multiple controls as a whole cause the decrease in voltages of specific nodes, leading to voltage collapse, in spite of normal individual operations. A criterion to detect the phenomena is derived and then a new control strategy based on this criterion is demonstrated. In this demonstration, unsuitably acting TCULs are individually deactivated at their most effective timings to improve voltage stability. The effectiveness of the proposed criterion and its application to the deactivation control have successfully been confirmed through numerical simulations in a radial network with three cascaded TCUL transformers, where a specific area of a real system is reduced to form the example system.
Flywheel generator. consist of a doubly-fed induction machine the secondary coil of which is fed and controlled by an inverter. has a feature of both effective and reactive power outputs in relatively quick response. The application of the machine for the enhancement of system dynamic stability has been discussed by simulations, where most calculations have been done based on phasor solutions. Targeting actual applications of flywheel generators. more accurate and precise calculation method, i.e. instantaneous value based one, has been desired. Recently Electro-Magnetic Transient Program (EMTP) has been significantly improved and, without special difficulty, instantaneous value based calculation of transient stability involving flywheel generator (s), inverter (s). synchronous machine (s) and actual system parameters has become realistic. This paper shows EMTP calculations of transient stability enhancement phenomena by flywheel generator, together with items necessary for application of EMTP for such calculations. Some results peculiar to instantaneous value based calculations are also shown.
In 1994 and 1995, a ground-to-ground microwave power transmission (MPT) experiment was carried out by a group of Kyoto University, Kobe University and Kansai Electric Power Company. Among the MPT technologies, which are one of the most important key issues for the realization of the Solar Power Satellite (SPS), studies of “rectenna” (rectifying antenna) have been pursued to archive higher efficiency of conversion from microwave to DC. We had developed a new rectenna panel which can effectively rectify a microwave power of 2.5W at 2.45GHz before the ground-to ground MPT field experiment. We examine the sum of the outputs of two or three rectenna panels in which are connected ether in parallel or in series or in the hybrid connection under the same microwave circumstances. The experiment leads us to conclude: (1) The sum of the DC outputs from two rectenna panels connected in parallel is larger than that from those connected in series. (2) The sum of the DC outputs of two rectenna panels is generally smaller than the sum of the DC output of the individual panels unless their output is equal to each other. (3) The total output DC power of a rectenna array increases when we connect the array element with consideration of the “element balance”. Based on the experiment, we propose an optimum method for connection of individual rectenna elements to form an rectenna array.
A difficult problem is encountered when the grounding resistance of a large grounding system is measured by the fall-of-potential method. The problem is that a horizontal curve section does not exist with a fall-of-potential curve. In this case it is difficult to estimate the grounding resistance from the fall-of-potential curve. In this paper, methods for determination of potential probe position to estimate the grounding resistance of a combination of horizontal and vertical electrode are proposed when horizontal curve section does not exist. First, for the electrode in two-layer ground, two methods are proposed. One is the method where the potential probe position is determined by application of the exact probe position for horizontal or vertical electrode. The other is the method where the potential probe is set at some point obtained here. This some point and error extents with the two methods are described. Next, for the electrode in three-layer ground, the potential probe is proposed to be set as some point obtained here. This some point and error extents in this case are also described.
NTT is developing a phosphoric-acid fuel-cell energy system for telecommunication co-generation systems to reduce energy costs and help preserve the environment. Fuel cells are used to provide electrical power to telecommunication equipment and the heat energy that is generated is used by the absorption refrigerators to cool the telecommunication rooms throughout the year. We fieldtested this fuel-cell energy system in a telephone office. Two heat recovery methods were applied in the test: one uses direct steam heat recovery from fuel-cell stack coolant to keep the heat recovery temperature high and to avoid requiring a heat exchanger for the recovery; the other uses heat recovery from the reformer exhaust gas that is directly in contact with the heat recovery water to recover heat more economically. Our field tests confirmed that the average efficiency of heat recovery from fuel-cell stack coolant is 16%, and from the reformer exhaust gas is 9% under 80-kW continuous operation. Maximum total efficiency including electrical power efficiency was comfirmed to be about 73% under the condition of 100-kW and an S/C ratio of 2.5 in the winter period: heat recovery from the fuel-cell stack coolant was 23%, from the reformer exhaust gas was 10%, and from electrical conversion was about 40%.
Heavy erosion of the electrode is a problem in using AC plasma torches. In a series of our studies, the effects of electrode stem size (diameter and length) and tip shape on the electrode erosion were clarified at a low current of 200A. In this paper, on the basis of the 200A-data, in order to reduce the electrode erosion with the current increased, the effects of current and electrode size on electrode erosion were clarified experimentally and analytically at 100-550A. The electrode used was of solid type and the material was tungsten containing 2 wt% of lanthanum oxide. The plasma gas was argon. Main results are as follows. (1) As the current increased, the electrode erosion increased linearly. In case of thin electrode(8mm φ), at 450-550A, the electrode tip was molten partially and the electrode erosion increased rapidly over 5mg/h. However, in case of thick electrode (13mm φ), the electrode erosion did not increase rapidly. (2) The temperature distribution along the electrode axis was calculated. As a result, a good correlation was obtained between the calculated temperature of electrode tip and the measured electrode erosion. As the tip temperature decreased to 3, 000K (c. f. tungsten melting point: 3, 660K), the electrode erosion decreased below 5mg/h of the linearly increasing range.
Effects of load resistance at nozzle on performance of disk MHD generator were investigated experimentally. Furthermore, a difference of electrical performances between a single load and segmented loads was studied. Experimental results indicated that an increase of static pressure at exit of the nozzle was not only due to Lorentz force in the nozzle but also to that in the MHD channel. This could be explained by the propagation of pressure increase at the MHD channel into the nozzle through boundary layer near walls. And it was found that load resistance at the nozzle affected Mach numbers, static pressures and Hall potentials at the inlet of the MHD channel. However, distributions of those values measured at middle-stream and downstream regions became almost the same. Therefore, influences of load resistance at the nozzle on enthalpy extractions remained small. When a single load was connected between the nozzle and the cathode, enthalpy extraction was reduced remarkably and this was due to a large Hall potential drop in the nozzle. Furthermore, it was found that there was a strong correlation between fluctuations of Hall currents in the nozzle and those in the MHD channel and that fluctuations of the currents in the nozzle were transmitted into the MHD channel by the flow. This suggests that non-uniformity of plasma in the nozzle affects strongly the uniformity of plasma in the MHD channel.
We observed current pulse waveforms of partial discharge (PD) in SF6 gas to investigate the PD mechanism. We also measured light intensity and light emission image of PD simultaneously under different condition of applied voltages and SF6 gas pressure. From these experiments, we found that the “double peaks current waveform” appeared at high pressure and high voltage condition. We also analyzed the mutual correlation of waveforms between a single current and the light emission. Moreover, we obtained the experimental evidence of filament like light image appeared at PD tip under the same condition with double peaks current waveform. From the electric field analysis around the needle electrode tip, we believe that the filament like light image expands beyond the critical electric field of SF6 gas. Thus, we concluded that these current waveforms with double peaks showed the evidence of leader type PD, leading to breakdown. Finally, we could point out that the leader type PD should be distinguished and measured for the diagnosis of GIS insulation performance.
We have already proposed a transformer model for transfer voltage, which consists of the EMTP TRANSFORMER model simulating the electromagnetic transfer component and some capacitances simulating electrostatic transfer component. The value of various parameters of this model are calculated from the actual measurements entailing no numerical calculations and help in understanding their physical relevance. In the subsequent discussion, however, we found it important to consider the frequency dependence of leakage inductance and core loss. This paper shows frequency dependence from tested results for many transformers, and studies the validity of the new transformer model by comparing the transformer model based on the frequency dependence with the tested results. The model is represented in the MODELS language description.
The breakdown characteristics in the gap with a thin dielectric sheet in an atmosphric air are investigated, experimentally. The breakdown phenomena are divided into three patterns by the current pulses. The first pattern consists of the primary pulse as a single pulse, the second pattern consist of secondary pulses as the successors of primary pulse, and the third pattern is growing process from the second pattern to the breakdown as a final stage. The flashover voltage of the sheet is irregular even if experimental condition is same. The breakdown voltage in a complex gap consists of air and thin sheet gaps became higher than that of thin sheet gap. These phenomena are analyzed by using an electric field distribution.
This paper describes the structure of an strain type FRP core for polymer composite insulator. The polymer composite insulator consists of an FRP core for mechanical force resistance, outdoor use polymer insulating materials as the housing, and metal end fittings, and is being examined to be applied as a substitute for the conventional porcelain insulator. The developed FRP core is used for mechanically straining the conductor. The FRP shaped like a race-track-coil and connected with the metal end fittings. A basic experiment was conducted by changing the number of glass fibers (number of rovings) of the FRP core. Based on the results of experiment and simulation to obtain tensile strength characteristic, samples of an FRP core corresponding to a maximum service tensile load of 50 kN were experimentally manufactured, and it was verified by a tensile load test that the FRP core has almost the intended mechanical performance.