Actual Hourly Research Articles

Development of simplified loss models for distribution system analysis

This paper proposes a methodology to derive a simplified model for distribution system loss analysis. According to the typical daily load patterns and the energy consumption of customers, the hourly loading of distribution transformers can be solved. A three-phase load flow program is applied to calculate the feeder power flow so that the hourly feeder loading will be the same as that obtained by the field test. The hourly primary conductor loss, secondary conductor loss, transformer copper loss and core loss are then solved according to the mathematical modeling of system components. The sensitivity analysis of system loss with respect to the feeder loading, power factor, feeder length, transformer capacity is then performed to derive the simplified loss model of distribution feeders. A distribution feeder of Taipower system is then selected for computer simulation to demonstrate the effectiveness of the proposed method. By applying the simplified loss model derived, the daily loss pattern of distribution feeders is solved according to the actual hourly feeder loading. It is concluded that the proposed methodology provides a useful tool for distribution engineers to estimate the operation efficiency of distribution systems in a very effective manner. >

Estimating the Time Dependence of Air Temperature Using Daily Maxima and Minima: A Comparison of Three Methods

Abstract Many models in a variety of disciplines require air temperature throughout the day as an input, yet often the only data available are daily extrema. Several methods for estimating the diurnal change in temperature from daily extrema have been reported. This paper compares the performance of three such algorithms (a sine wave, a sine-exponential, and a linear model) at all times of the year. Each was used to generate four years of hourly temperatures using as input the daily highs and lows recorded by the National Weather Service at the Minneapolis-St. Paul International Airport for the years 1970, 1971, 1973 and 1974. The output from the models was compared with the actual hourly values recorded at the same site. Residual sums and standard errors computed for all three models, both as functions of day and month of the year, showed that all three were more accurate in summer than in winter. Differences in the overall standard errors of estimate among the three models were small relative to the sta...

Evaluation of Diurnal Temperature Models and Thermal Summation in New Zealand

Five methods of degree-day (DD) estimation using diurnal temperature models were evaluated. Seasonal data for a 5-yr period from nine locations throughout New Zealand were used to compare estimated and actual DD summations over time. All models tested showed variable efficiency in the estimation of accumulated DD among localities and seasons. Results suggest that actual hourly temperatures should be used for DD calculations in climates that have a highly variable weather pattern with low average temperatures relative to the threshold used.

A bispectral method for determining global solar radiation from meteorological satellite data

A bispectral method is presented for determining the global solar radiation at the earth's surface. The technique involves the use of VISSR data from GMS-3 to obtain cloud parameters which affect the incoming solar radiation, namely fractional cloud amount and cloud albedo. The fractional cloud amount is derived from the infra-red data and the cloud albedo from the visible data, respectively. The two effects are then combined into a single parameter for cloud effectiveness. It was found that the cloud effectiveness is linearly correlated with the atmospheric transmissivity. The regression parameters were estimated from a training data set with the help of pyranometers on the ground. The regression model was then tested by comparison with the estimated solar radiation for another time period and area. The results showed good agreement between the actual and model-derived hourly and daily global radiation with standard errors less than 12% and 14% of the mean, respectively.

Crop Moisture Stress Analysis Using Computer-Controlled Environmental Chambers and Simulated Weather Sequences

ABSTRACT COMPUTER-CONTROLLED environmental plant growth chambers (PGC) were used to measure responses of water stressed and non-stressed corn and soybeans to simulated weather sequences. Simulated weather was patterned after actual hourly environmental conditions measured during a previous summer with a CR-21 weather station. Seasonal and diurnal crop water use in the PGC was controlled and monitored with an electronic lysimeter and a second computer system. Seasonal crop phenological responses were measured and show a remarkable pattern of stages of growth similar to field plants. LAST DAY measurements seed dry matter and seed number gave from 15.0 to 20.1 g per 100 seed and from 5 to 60 fruits per plant for soybeans. The PGC can be used to elicit the upper and lower limit growth responses to moisture-stress for certain crops.

Wind-Energy Conversion System Simulation Program

This paper describes a program which was developed to simulate the operation and performance of a windenergy conversion system (WECS) for a nonutility potential user, and to perform a lifecycle economic analysis. The system consists of a wind turbine in conjunction with purchased utility power and an optional energy storage system and heat engine. Because of the site-specific nature of WECS, the program parameters are characteristic of the WECS site being simulated; e.g., the site's wind-velocity data, the nonutility owner's timevarying process energy requirements, the specific performance of the WECS installed equipment, and the owners's investment structure. The wind is described using actual hourly velocity data, or by a given statistical function and sampling for specified time periods. In the simulation, a WECS process controller determines operating strategy, which is to first use wind-generated energy, followed by the storage system and then the heat engine, if installed. Any remaining energy shortfall is purchased from the utility, while excess WECS energy generated is sold to the utility. The lifecycle economic analysis calculates annual savings after taxes, investment payback time period, and return on investment. To demonstrate the use of the program, a hypothetical system is described and analyzed.

AGRICULTURAL METEOROLOGY: SOME CHARACTERISTICS OF WINDS IN ALBERTA AND SASKATCHEWAN

Over a period of years, the monthly mean mileage of wind per day during the six months, April to September, at four meteorological stations in central and southern Alberta and Saskatchewan is greatest in April and May, and least in July and August. In all cases the range of variation of the monthly means is considerable, being of the order of 50%. Significant correlation in the inter-annual fluctuations at the four stations is not demonstrable from the available data, but there is some indication of correlation between the mileages at a given station in successive months of the same year. During the season as a whole, northwesterly winds predominate, but in this respect also there are pronounced annual variations.Variation in the amount of wind from day to day within months is also pronounced, and tables are presented showing for each of the six months the relative frequency of occurrence of different daily mileages.On the whole, more wind is recorded during the daytime than at night. The hourly averages for all six months show a definite diurnal trend, the maximum being in the vicinity of 3 p.m., but the actual hourly sequence on a given day may deviate markedly from this underlying regularity. There is a slight tendency for days of above-average temperature to have a higher wind mileage, but this is a minor factor in comparison with the uncorrelated variation of both quantities.