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IEE Proceedings C (Generation, Transmission and Distribution)

Volume 130, Issue 5, September 1983

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Volume 130, Issue 5

September 1983

State forecasting in electric power systems
  • Author(s): A.M. Leite da Silva ; M.B. Do Coutto Filho ; J.F. de Queiroz
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 130, Issue 5, p. 237 –244
  • DOI:  10.1049/ip-c.1983.0046
  • Type: Article
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  • p. 237 –244 (8)
    The state vector of a power system varies with time owing to the dynamic nature of system loads. Therefore, it is necessary to establish a dynamic model for the time evolution of the state vector. The dynamic state estimation approach consists of predicting the state vector based on past estimations, followed by a filtering process performed when a new set of measurements is available. This paper presents a new algorithm for forecasting and filtering the state vector, using exponential smoothing and least-squares estimation techniques. The proposed algorithm is compared with another one based on standard Kalman filtering theory. Numerical results showing the performance for both dynamic estimators under different operational conditions are presented and discussed. Detection and identification of multiple bad data are also included. The new dynamic estimator exploiting state forecasting is extremely useful to real-time monitoring of power systems.
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Statistical approach to thermal rating of overhead lines for power transmission and distribution
  • Author(s): C.F. Price  and  R.R. Gibbon
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 130, Issue 5, p. 245 –256
  • DOI:  10.1049/ip-c.1983.0047
  • Type: Article
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  • p. 245 –256 (12)
    The rating of an overhead line is limited by the maximum temperature it is permitted to reach. This temperature is chosen at the design stage along with the size of conductor, the height and spacing of the towers and overall optimisation of the design to meet the required balance between capital and revenue costs. Outside the control of the designer is the complex and variable cooling effect of the weather on the conductor. Fortunately the three basic parameters of wind, sun and air temperature do not each reach their extreme values for minimum cooling simultaneously. Hitherto, the degree of noncoincidence of these extreme values has been difficult to quantify owing to a lack of data on wind speeds below 1 m/s. Research work at CERL has provided comprehensive data on the incidence of low wind speeds, together with simultaneous values of wind direction, insolation and ambient air temperature. The temperature of a typical transmission conductor (400 mm2 ACSR, Zebra) carrying full-load current was also recorded. The variations in this conductor temperature reflected the varying cooling effect of the weather parameters. The range over which the conductor temperature varied was divided into 5 deg C intervals, and the percentage of time that the conductor temperature was in each interval was calculated. The data was divided into three seasons for the purpose of the analysis. A relationship was then established between the time that the conductor exceeded any given design temperature and the ratio of the heat input under test to the heat loss that would occur under design conditions. This relationship was found to provide a correlation of the data for the three seasons, which was then used with existing heat transfer data to predict the rating of any conductor for any chosen design temperature and selected percentage of total time that the conductor may exceed that temperature. In practice, system design and security standards restrict actual continuous loadings, and lines are generally operated at a fraction of their full thermal rating. This permits the selection of higher continuous ratings on a statistical basis. Applying the same statistical basis to the conditions prior to and during a fault condition permits an improvement in the overload rating. The overload approach permits the selection of continuous and overload ratings for overhead lines on a statistical basis, which is determined by the various system design and security standards and the cooling effect of the weather.
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Microprocessor-based identification system applied to synchronous generators with voltage regulators
  • Author(s): R.D. Lang ; M.A. Hutchison ; H. Yee
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 130, Issue 5, p. 257 –265
  • DOI:  10.1049/ip-c.1983.0048
  • Type: Article
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  • p. 257 –265 (9)
    With the need to improve the operation and control of existing generating units and to provide accurate information for the design of new units, better transfer function models and estimates of system parameters are required. This involves the identification of individual generator and voltage regulator parameters as well as system modes of oscillation and damping. The problem is to experimentally determine this information, simply, quickly and accurately. For this reason, system identification techniques are of interest to power engineers. In the paper, an identification technique involving pseudo-random ternary noise injection and cross correlation is assessed and applied to power systems. The theoretical basis, advantages and limitations of this method are examined and it is shown that the entire process of signal generation, injection, response measurement and crosscorrelation can be performed in real time using a dedicated microprocessor system. The identification technique is tested on a simple microalternator connected to a noisy power system through a transmission line. It is shown that under normal operating conditions a highly accurate system impulse response can be obtained and that the parameters of the machine and its voltage regulator can be estimated from this result. The technique is also applied to an open-circuited microalternator with a more complex voltage regulator and estimates of the regulator parameters are found with good accuracy.
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Hilbert transform in impulse functions of power-transmission-line electromagnetic transient model
IEE North Eastern Centre: Chairman's address. Electricity supply—the changing phases

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