Actual Surge Research Articles

Storm Surge Forecasting for the Arabian Sea

The results of the location specific IIT storm surge model reported in this study are in good agreement with the available actual peak surge observations. It was found that cyclones landfalling from the southwest direction generated larger surges than cyclones landfalling perpendicular or from the southeast. Moreover, a perpendicularly landfalling cyclone creates maximum surges at the eastern parts of the coastal region as compared to the other parts. It was verified that the storm surge is very sensitive to basin depths. The shallowness of the water in coastal areas may considerably magnify the surge heights in the region. The model has the ability to investigate multiple forecast scenarios in real time and can update cyclone tracks as the cyclonic storm approaches the coast and meteorological forecasts become more accurate. In comparison to the Bay of Bengal, the Arabian Sea in general and Pakistani coasts in particular are less vulnerable to tropical storms, geographically and bathymetrically. Ocean basins in the north Arabian Sea near Pakistan have depths more than 20 m, which helps to avoid huge storm surges.

Poverty Impact of Commodity Price Boom Using Household Survey - The Case of Maize in Zambia

This paper uses Household Survey data to analyze the possible effects that a food price surge could have on poverty and overall welfare. In particular, we use the Zambian Living Conditions Monitoring Survey I collected in 1996 (LCMS I) to estimate a demand system that enables us to simulate various price scenarios for the Zambian main staple and its possible effects for different population categories. Differently from previous studies, in our demand system we address two flaws usually encountered in this type of applications: one is the possible selection bias due to non-consumption of a particular staple among households, the other is the difference between the quantity used for estimation (typically logarithm) and the quantity of interest (level). Jointly, this increases the reliability of our technique. Our results show that a 50 percent increase in maize prices, which is in line with the actual surge in Zambia, could lead to an average consumption decrease of 17 percent among Zambian households and overall poverty could rise from 40 percent to 43 percent fairly quickly at national level.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - breakdown characteristics in the presence of bias voltages under non-uniform electric field

To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the previous work, the dielectric breakdown voltage - time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gap and partly the cone-shaped insulating spacers that represent an insulation element of GIS for six kinds of non-standard lightning impulse waveforms associated with lightning surges and disconnector switching surges. This paper, describes detailed examination in non-uniform electric field, and the pattern in which a disconnector switching surges are superposed on residual DC elements generated through the operation of disconnectors (bias voltages). This is intended to simulate more severe conditions in an actual system. Consequently, it was found that the presence of a bias voltage in the nonuniform electric field resulted in lower breakdown voltage values for single-frequency oscillation waveforms both in the positive and negative polarities. However, the breakdown voltage values under positive-polarity waveforms posing more severe insulation conditions were higher than the ones under the standard lightning impulse waveforms. Despite the presence of a bias voltage, it was possible to evaluate these breakdown voltage values in the positive polarity using the concept of a duration examined in the past.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms -

To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six kinds of non-standard lightning impulse waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Then, the dielectric breakdown voltage iquest time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gaps and partly the coneshaped insulating spacers that represent insulation elements of GIS for six kinds of nonstandard lightning impulse waveforms. In this paper, the resultant breakdown voltages were evaluated in terms of the overvoltage duration, which led to their formulation in a unified way. On the basis of these insulation characteristics and their unified formulation, the paper investigated a method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. When the constructed algorithm was applied to five examples of representative two type waveforms in the lightning surge time region, they were converted into standard lightning impulse waveforms with crest values reduced by 20% to 34%, suggesting potentiality for reduction of lightning impulse insulation specifications of GIS.

ガス絶縁開閉装置の非標準雷インパルス波形に対する不平等電界下での絶縁破壊特性

To improve insulation specification of a gas insulated switchgear (GIS), it is necessary to recognize the insulation characteristics of SF6 gas under actual surge (called non-standard lightning impulse waveform) occurring in the field substation. The authors had observed the insulation characteristics of SF6 gas gap under various types of non-standard lightning impulse waveforms and compared them with under standard lightning impulse waveform quantitatively. From the investigation of the experimental results, the evaluation method for real surges is shown and the method is applied to typical surges for various UHV and 500kV systems. In the proceeding study, therefore, only for the quasi-uniform electric field (with a typical range of the field utilization factors in the bus of a GIS) was investigated. In this paper, the insulation characteristics of SF6 gas gap for non-uniform electric field were observed experimentally and investigated about the evaluation method of converting non-standard lightning impulse waveforms equivalently to the standard lightning impulse waveform.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - breakdown characteristics under non-uniform electric field

To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, the dielectric breakdown voltage-time characteristics were measured under several different conditions on the quasi-uniform SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas gap and partly the cone-shaped insulating spacers that represent an insulation element of GIS for six kinds of non-standard lightning impulse waveforms associated with lightning surges and disconnector switching surges. This paper describes obtaining through experiments the insulation characteristics for single-frequency oscillation waveforms as a representative waveform when there is a non-uniform electric field represented by metallic particles in the equipment while changing the applied voltage polarities, frequencies, and damping factors. As a result, it was found that the dielectric breakdown voltages are lower in the positive polarity and it was confirmed appropriate to conduct experiments mainly in positive-polarity in order to consider dielectric strengths. Furthermore, changing the frequencies and damping factors under positive-polarity waveforms did not cause major changes in the feature of the dielectric breakdown voltages, which remained constantly higher (by 1.41 to 2.58 times) than those under standard lightning impulse waveforms.

Evaluation of breakdown characteristics of oil-immersed transformers under non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus reduce equipment cost while maintaining high insulation reliability, it is required to identify the insulation characteristics under non-standard lightning impulse waveforms that are associated with actual surge waveforms in the field and quantitatively compare them with the characteristics under the standard lightning impulse waveform. In the previous research, field overvoltages in the lightning surge time region were analyzed, and four typical non-standard lightning impulse waveforms were defined. These four waveforms were used to measure the breakdown voltages and the partial discharge inception voltages on three models of the winding insulation elements of oil-immersed transformers. The average breakdown voltages were evaluated in terms of the overvoltage duration. This paper describes a method for converting of non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. The constructed algorithm was applied to four examples representing two types of non-standard lightning waveforms. Due to the conversion into standard lightning impulse waveforms, the crest values were reduced by 14% to 26%. This seems to be a potential for reduction of lightning impulse insulation specifications of oil-immersed transformers.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms under diverse conditions

To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, the dielectric breakdown voltage-time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gap and partly the cone-shaped insulating spacers that represent an insulation element of GIS for six kinds of non-standard lightning impulse waveforms associated with lightning surges and disconnector switching surges. As a result, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than those for the standard lightning impulse waveform by 3% to 36%. In these experiments, parameters other than waveforms were fixed to standard conditions. In this paper insulation characteristics on quasi-uniform SF6 gas gaps were examined while changing conditions on gas pressures, gap lengths, electrode surface roughness, voltage polarities, and bias voltages. As a result, it was confirmed that the results under standard experimental conditions in the preceding experiments can be applied widely to the GIS actual equipment conditions.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - breakdown characteristics for non-standard lightning impulse waveforms associated with disconnector switching surges -

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding paper, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. In this paper, the dielectric breakdown voltage - time characteristics were measured under several different conditions for the quasi-uniform SF6 gas gap that represents an insulation element of a GIS toward two kinds of non-standard lightning impulse waveforms associated with disconnector switching surges. As a result, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 6% to 36%.

Evaluation of Breakdown Characteristics of Gas Insulated Switchgears for Non-Standard Lightning Impulse Waveforms - Breakdown Characteristics for Non-Standard Lightning Impulse Waveforms Associated with Lightning Surges

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding paper, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. In this paper, the dielectric breakdown voltage - time characteristics were measured under several different conditions mainly for the quasi-uniform SF6 gas gaps that represent an insulation element of a GIS toward four kinds of non-standard lightning impulse waveforms associated with lightning surges. As a result, in the tested range, the dielectric breakdown values for nonstandard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 3% to 32%.

Evaluation of breakdown characteristics of oil-immersed transformers under non-standard lightning impulse - insulation characteristics for non-standard lightning impulse waveforms with oscillations

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus reduce equipment cost while maintaining high insulation reliability, it is important to identify the insulation characteristics under non-standard lightning impulse waveforms that are associated with actual surge waveforms in the field besides the standard lightning impulse waveform and quantitatively compare them with the characteristics under the standard lightning impulse waveform. In a preceding paper, field overvoltages in the lightning surge time region were analyzed, and four typical non-standard lightning impulse waveforms were identified. Two of these including pulses were used to measure the breakdown voltages and the partial discharge inception voltages while changing the parameters, on three models of the winding insulation elements of oil-immersed transformers. This paper investigates the insulating properties of the other two types: "damped-oscillation waveform" and "rising-oscillation waveform", and evaluates the resultant average breakdown voltages in terms of the overvoltage duration, permitting their formulation in a unified way. In the examined range, the dielectric breakdown values under non-standard lightning impulse waveforms were up to 50% higher than those under standard lightning impulse waveforms in all cases. Further investigations will be expected for the reduction in insulation specifications.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - analysis and generation circuit of non-standard lightning impulse waveforms in actual field

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In this paper, first, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Next, high-voltage circuits that generate these non-standard lightning surge waveforms were designed and constituted using EMTP (electro magnetic transients program) based on a circuit with a gap, inductors, and resistors connected in series and resistors and capacitors connected in parallel. Further, circuits were actually constructed, to obtain voltage waveforms approximately equal to those designed. Finally, the dielectric breakdown voltage-time characteristics were measured under several different conditions for the quasi-uniform SF6 gas gap that represents an insulation element of a GIS. As a result, it was found that, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 6% to 32%

Evaluation of breakdown characteristics of oil-immersed transformers under non-standard lightning impulse waveforms - definition of non-standard lightning impulse waveforms and insulation characteristics for waveforms including pulses

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus cut the equipment cost while maintaining the high reliability in its insulation performance, it is necessary to grasp in an organized way the insulation characteristics under non-standard lightning impulse voltage waveforms that represent actual surge waveforms encountered in the field and compare them with the characteristics under the standard lightning impulse waveform quantitatively. As described in this paper, the first step in a series of study for the purpose above was taken by analyzing lightning surge waveforms and restriking surge waveforms such as disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations and identifying four typical non-standard lightning impulse waveforms with basic frequencies of 0.24 to 1.0 MHz. Then, two of these non-standard lightning impulse waveforms, the single-pulse waveform which is the most basic type and the waveform with a pulse in the crest and a subsequent flat section, were used to measure the breakdown voltage and the partial discharge inception voltage while changing the parameters, on three models that represent the insulation elements of windings of oil-immersed transformers. Then, the resultant average breakdown voltages were evaluated in terms of the overvoltage durations, leading to a result of formulating them in a unified way. In the tested range, the dielectric breakdown values under non-standard lightning impulse waveforms were higher, marking 52% at the maximum, than those under standard lightning impulse waveforms in all the cases, suggesting a possibility of lowering the insulation specifications of an oil-immersed transformer

Performance of cold compressors in a cooling system of an R&D superconducting coil cooled with subcooled helium

The helical coils of large helical device (LHD) have been operated in saturated helium at 4.4 K and plasma experiments have been carried out at magnetic fields lower than 3 T for 8 years. Now, it is considered that the cooling system of helical coils will be improved to enhance magnetic fields in 2006. In the improvement, the helical coils will be cooled with subcooled helium and the operating temperature of helical coils will be lowered to achieve the designed field of 3 T and enhance cryogenic stabilities. Two cold compressors will be used in the cooling system of helical coils to generate subcooled helium. In the present study, the performance of cold compressors has been investigated, using a cooling system of R&D coil, to apply cold compressors to the cooling system of helical coils. Actual surge lines of cold compressors were observed and the stable operation area was obtained. Automatic operations were also performed within the area. In the automatic operations, the suitable pressure of a saturated helium bath, calculated from the rotation speed of the 1st cold compressor, was regulated by bypass valve. From these results, stable operations will be expected in the cooling system of helical coils.

Estradiol Requirements for Induction and Maintenance of the Gonadotropin-Releasing Hormone Surge: Implications for Neuroendocrine Processing of the Estradiol Signal*

Two experiments were performed to examine the temporal requirements of the estradiol signal for the GnRH and LH surges in the ewe. Hypophyseal portal and jugular blood (to measure GnRH and LH, respectively) were sampled from ewes set up in an artificial follicular phase model. After progesterone withdrawal to simulate luteolysis, circulating estradiol was raised to a preovulatory level by inserting estradiol implants, which then were removed at different times to vary estradiol signal duration. The objective of the first experiment was to assess the effect of withdrawing estradiol at surge onset on development and maintenance of the GnRH/LH surges. Removal of estradiol, before surge onset, neither altered the LH surge in relation to that induced when the estradiol stimulus was maintained nor affected stimulation of a massive and sustained GnRH surge that outlasted the LH surge by many hours. Continued estradiol treatment, however, did prolong the GnRH surge. In the second experiment, the estradiol stimulus was shortened to test the hypothesis that estradiol need not be present for the whole presurge period to induce GnRH/LH surges. Ewes received estradiol either up to the time of surge onset (21 h) or for periods equivalent to the last 14 h, the last 7 h, or the earliest 7 h of the 21-h signal. Shortening the signal to 14 h did not reduce its ability to stimulate a full GnRH surge, but it did reduce the amplitude of the resultant LH surge. Further shortening of the signal to 7 h, however, produced a mixed response. Most animals (8 of 10 combining the two 7-h groups) did not express GnRH surges. In the two ewes that did, GnRH surge amplitude and duration were again within the range observed with the 21-h estradiol signal, but the LH response was greatly reduced. These results indicate that, once the GnRH/LH surges of the ewe have begun, elevated estradiol is not required for surge maintenance. Development of a full GnRH surge requires elevated estradiol for only a portion of the presurge period. More prolonged exposure to estradiol, however, is needed to maximize pituitary responsiveness to GnRH. Since the estradiol signal for the GnRH surge is relatively short (7-14 h) and temporally located well in advance of the surge itself, these results are consistent with the hypothesis that estradiol is required only to activate the steroid-responsive neuronal elements and not for progression of the signal from these elements to the actual surge process of GnRH release.

Designing for immortality (surge environment)

Electrical transients from lightning and power utility fluctuations frequently damage equipment powered from an AC line. The authors discuss the actual surge environment, based on the analysis of a large installed base of commercial surge protectors. This analysis is based mainly on new information resulting from a review of returns for warranty service of commercial surge protectors. The data from warranty repair records has been combined with that from the literature to understand the customer environment. The authors show the range of transients that could be encountered in actual installations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Influence of surge diverters on overvoltage probability distributions

The paper considers the effectiveness of modern surge diverters as a means of controlling the overvoltages that occur during switching in power-transmission networks. The requirements and method of realisation of a comprehensive model, capable of simulating the performance of actual high-voltage surge diverters, are discussed. The model is used in an existing transient-network-analyser facility under the control of a small digital computer, and the system has been programmed to perform Monte Carlo testing to determine overvoltage probability distributions. In this way, the sensitivity of overvoltage distributions to variations in surge-diverter characteristics is investigated. The effects of changes in the statistical parameters associated with diverter sparkover and the characteristics of active-gap performance are examined, and conclusions offered in relation to the protective level assured by surge diverters

A NEW NUMERICAL METHOD APPLIED TO THE STUDY OF MASS OSCILLATIONS IN A PUMPED STORAGE HYDRO-ELECTRIC SCHEME.

Mr R . J. T. Casinader, Binnie and Partners Methods previously suggested for numerical or graphical solution of the problem of mass oscillations in hydraulic surge systems have, for all real cases, been in one form or another step-by-step integration procedures. The new method now proposed by the Authors breaks no new ground in this respect. While accepting that the governing equations can only be solved in closed analytical form for a limited number of cases, I still hope that a more elegant method will some day be devised for dealing with the problem. The refinement of the extrapolation technique proposed by the Authors is, however, a notable contribution to the subject. 52. The digital computer has, as the Authors mention, been used in conjunction with simple step-by-step integration methods, its main advantage being the facility of using smaller step sizes than would normally be used in hand or graphical computations. The limitation is of course the onset of instability as the step size is reduced, that is, instability in the computations rather than the actual surge. The Authors’ method is designed from the outset to avoid this instability at each step. However, it should be possible when using a digital computer with a simple step-bystep method, say the Heun method, to carry out successive runs using smaller and smaller step sizes until instability is induced. One or two such runs on any system should indicate the smallest step size that should be employed to obtain reasonable accuracy without inducing instability in the computations. The method is, in effect, to apply the equivalent of the Authors’ convergence, or accuracy, test and divergence test to the whole calculation rather than to each step. 53. The Authors’ views on the merits of this procedure relative to those of the method they propose would be of interest, bearing in mind the relative computational costs of each method. The simpler method should be suitable for the analysis of much more complicated surge systems than that analysed by the Authors. Would the Authors’ method be equally suitable for dealing with systems of, say, two or more surge tanks? 54. The new method has apparently been devised specifically for dealing with surges in pumped storage hydro-electric systems. Such systems have particular characteristics, which, although not exclusive to pumped storage schemes, have a bearing on the most suitable method of analysis. The schemes are generally high head with relatively short headrace and/or tailrace tunnels of large cross section. Friction losses are therefore relatively low. Surges in such systems have the following general characteristics: (a) amplitudes are low relative to total head on the system; (b) the period of the oscillations is short; (c) damping of the oscillations is poor.

The Apple Grove 750-kV Project- 500-kV Switching Surge and Line Flashover Tests

Rational design of extra-high-voltage systems depends on analytic studies to predict switching surge overvoltage magnitude and probability, and on laboratory tests for tower system switching surge withstand capability. Laboratory tests have been confined to ideal waveforms applied to single window configurations. Correlation with flashover performance of a typical 3-phase installation exposed to actual switching surge waveforms is attempted. The influence of interphase coupling and multiple circuit breaker operations in promoting multiphase flashover, which may curtail system performance margins, is also studied.

Lightning Discharges and Line Protective Measures

This paper describes the mechanics of the development of a lightning stroke in a cloud and the formation of a surge on a line. It shows that the energy of a stroke can vary between wide limits so that the actual surge on the line may be of practically any magnitude. Fundamental types of high-tension line construction are analyzed to show the performance that would be obtained with them. Experience obtained on the 220-kv. lines of the Public Service Electric and Gas Company is offered to substantiate the belief that induced surges are of relatively small importance and that the direct stroke is the criterion for good design. The effects of line construction on the character of surges impressed on the terminal substation apparatus is discussed to indicate the degree of protection that would be required.