87,595 research outputs found
A Recipe for State-and-Effect Triangles
In the semantics of programming languages one can view programs as state
transformers, or as predicate transformers. Recently the author has introduced
state-and-effect triangles which capture this situation categorically,
involving an adjunction between state- and predicate-transformers. The current
paper exploits a classical result in category theory, part of Jon Beck's
monadicity theorem, to systematically construct such a state-and-effect
triangle from an adjunction. The power of this construction is illustrated in
many examples, covering many monads occurring in program semantics, including
(probabilistic) power domains
Developments in space power components for power management and distribution
Advanced power electronic components development for space applications is discussed. The components described include transformers, inductors, semiconductor devices such as transistors and diodes, remote power controllers, and transmission lines
Optimal passive filter design for effective utilization of cables and transformers under non-sinusoidal conditions
Transformers and cables have overheating and reduced loading capabilities under non-sinusoidal conditions due to the fact that their losses increases with not only rms value but also frequency of the load current. In this paper, it is aimed to employ passive filters for effective utilization of the cables and transformers in the harmonically contaminated power systems. To attain this goal, an optimal passive filter design approach is provided to maximize the power factor definition, which takes into account frequency-dependent losses of the power transmission and distribution equipment, under non-sinusoidal conditions. The obtained simulation results show that the proposed approach has a considerable advantage on the reduction of the total transmission loss and the transformer loading capability under non-sinusoidal conditions when compared to the traditional optimal filter design approach, which aims to maximize classical power factor definition. On the other hand, for the simulated system cases, both approaches lead to almost the same current carrying (or loading) capability value of the cables. © 2014 IEEE.This work is supported by Turkish Republic Ministry of Science, Industry and Technology and BEST Transformers Co. under the project number of 01008.STZ.2011 - 2
Apparatus including a plurality of spaced transformers for locating short circuits in cables
A cable fault locator is described for sensing faults such as short circuits in power cables. The apparatus includes a plurality of current transformers strategically located along a cable. Trigger circuits are connected to each of the current transformers for placing a resistor in series with a resistive element responsive to an abnormally high current flowing through that portion of the cable. By measuring the voltage drop across the resistive element, the location of the fault can be determined
UHF diagnostic monitoring techniques for power transformers
This paper initially gives an introduction to ultra-high frequency (UHF) partial discharge monitoring techniques and their application to gas insulated substations. Recent advances in the technique, covering its application to power transformers, are then discussed and illustrated by means of four site trials. Mounting and installation of the UHF sensors is described and measurements of electrical discharges inside transformers are presented in a range of formats, demonstrating the potential of the UHF method. A procedure for locating sources of electrical discharge is described and demonstrated by means of a practical example where a source of sparking on a tap changer lead was located to within 15 cm. Progress with the development of a prototype on-line monitoring and diagnostic system is reviewed and possible approaches to its utilization are discussed. New concepts for enhancing the capabilities of the UHF technique are presented, including the possibility of monitoring the internal mechanical integrity of plant. The research presented provides sufficient evidence to justify the installation of robust UHF sensors on transformer tanks to facilitate their monitoring if and when required during the service lifetime
Prediction of remaining life of power transformers based on left truncated and right censored lifetime data
Prediction of the remaining life of high-voltage power transformers is an
important issue for energy companies because of the need for planning
maintenance and capital expenditures. Lifetime data for such transformers are
complicated because transformer lifetimes can extend over many decades and
transformer designs and manufacturing practices have evolved. We were asked to
develop statistically-based predictions for the lifetimes of an energy
company's fleet of high-voltage transmission and distribution transformers. The
company's data records begin in 1980, providing information on installation and
failure dates of transformers. Although the dataset contains many units that
were installed before 1980, there is no information about units that were
installed and failed before 1980. Thus, the data are left truncated and right
censored. We use a parametric lifetime model to describe the lifetime
distribution of individual transformers. We develop a statistical procedure,
based on age-adjusted life distributions, for computing a prediction interval
for remaining life for individual transformers now in service. We then extend
these ideas to provide predictions and prediction intervals for the cumulative
number of failures, over a range of time, for the overall fleet of
transformers.Comment: Published in at http://dx.doi.org/10.1214/00-AOAS231 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A study of life time management of Power Transformers at E. ONâs Ăresundsverket, Malmö
The objective of this master thesis is to review the present and future condition of generator step up power transformers at the combined heat and power plant Ăresundsverket, in Malmö. The objective of this work was to prolong the lifetime of power transformers at Ăresundsverket. The thermal properties of power transformer are been taking into consideration for their life time assessment. The most suitable thermal model was chosen which can prolong life to these transformers in the future. Electrical, mechanical and chemical properties of power transformers were taking in account for evaluation. The comparisons were made between different calculated models to find the most suitable thermal model for transformers
Three-phase five limb transformer responses to geomagnetically induced currents
Geomagnetically induced currents (GIC) are quasi-DC currents that result from space weather events arising from the sun. The sun ejects hot plasma in a concept termed âcoronal mass ejections' which is directed towards the earth. This plasma interferes with the magnetic field of the magnetosphere and ionosphere, and the magnetic field is subsequently distorted. The distortions in these regions results in the variation of potential on the earth's surface and distortions in the earth's magnetic field. The potential difference between two points on the earth's surface leads to the flow of direct current (DC) of very low frequency in the range 0.001 ~ 0.1 Hz. Geomagnetically induced currents enter into the power system through grounded neutrals of power transformers. The potential effects of GIC on transformers are asymmetrical saturation, increased harmonics, noise, magnetization current, hot spot temperature rise and reactive power consumption. Transformer responses to GIC was investigated in this research focussing on a three-phase fivelimb (3p5L) transformer. Practical tests and simulations were conducted on 15 kVA, 380/380 V, and 3p5L transformers. The results were extended to large power transformers in FEM using equivalent circuit parameters to show the response of grid-level transformers. A review of literature on the thresholds of GIC that can initiate damage in power transformers was also done and it was noted that small magnitudes of DC may cause saturation and harmonics to be generated in power transformers which may lead to gradual failure of power transformers conducting GIC. Two distinct methods of measuring power were used to measure reactive power consumed by the transformers under DC injection. The conventional method and the General Power Theory were used and the results show that the conventional method of measuring power underestimates reactive power consumed by transformers under the influence of DC injections. It may mislead system planners in calculating the reactive power reserves required to mitigate the effects of GIC on the power system
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