Switchgear Transformers - IEEE Xplore

4 downloads 0 Views 362KB Size Report
peak current and about 25% or more of the return stroke charge trans- ferred in the first millisecond passed to the neutral conductor through each of the two ...
peak current and about 25% or more of the return stroke charge transferred in the first millisecond passed to the neutral conductor through each of the two closest arresters on either side of the strike point. The bulk of the peak current then flowed from the neutral conductor to ground through the groundings of the two closest arresters. The charge transferred in the first millisecond from the neutral to the eight system groundings, six at arrester stations and one at each of the two line-end poles, appears to be distributed inversely to the low-frequency, low-current grounding resistances. From our measurements of return stroke current division and in view of the available data on the currents of first strokes in natural lightning, we estimate that over half of natural first strokes would result in an arrester failure in our test distribution line, which is representative of some distribution lines in service, within about 450 ,us of the initiation of the first return stroke current flow, in the absence of fiashovers and other altemative current paths that might be provided by transformers or underground cable connections to allow the stroke current to bypass the arrester. Additional first stroke current flow beyond about 450 gs and currents associated with subsequent strokes and potentially other processes should further increase the likelihood of arrester failure. Keywords: Lightning, MOV arresters, grounding electrodes, power distribution lines. Preprint Order Number: PE-139PRD (06-2002) Discussion Deadline: November 2002

Switchgear New Fault Diagnosis of Circuit Breakers Lee, Dennis S.; Lithgow, Brian; Morrison, R.E. Author Affiliation: Monash University. Abstract: Wavelet packets and neural networks have been used to analyze the vibration data of circuit breakers for the detection of incipient circuit breaker faults. Wavelet packets are used to convert measured

Keywords: Linear variable transformer, transformer, short circuit impedance, finite element analysis. Preprint Order Number: PE-253PRD (06-2002) Discussion Deadline: November 2002

Reducing Losses in Distribution Transformers Olivares, Juan Carlos; Liu, Y; Canedo, J.; Escarela-Perez, R.; Driesen, J.; Moreno, P

Author Affiliation: Virginia Polytechnic Institute and State University; CINVESTAV; Katholieke Universiteit Leuven; Universidad Autonoma Metropolitana-Azcapotzalco. Abstract: This paper examines three methods of reducing distribution transformer losses. The first method analyzes the effects of using aluminum electromagnetic shields in a distribution transformer. The goal of placing electromagnetic shields in the distribution-transformer tank walls is to reduce the stray losses. A 500 kVA shell-type transformer was used in the experiments. The overall results presented indicate that stray losses can be considerably reduced when electromagnetic shielding is applied in the transformer tank. In the experiment, the tank walls were lined with aluminum foil. The possibility of reducing the dielectric losses was shown through experiments in the second method. The third method analyzes the behavior of wound-cores losses in distribution transformers as a function of joint configuration design parameters. The joint configuration used in this paper is called step-lap joint. Keywords: Dielectric losses, loss measurements, shielding, transformer, transformer cores. Preprint Order Number: PE-394PRD (06-2002) Discussion Deadline: November 2002

Proposed Standards for Frequency Conversion Factors of Transformer Performance Parameters

Design of a High Power Brushless Linear Variable Transformer

Girgis, Ramsis S.; Beaster, B.; teNyenhuis, Ed G. Author Affiliation: ABB Power T&D Company Inc.; ABB Power Transformers. Abstract: This paper presents the development of appropriate frequency conversion factors for performance parameters of transformers. These factors are needed in order to allow manufacturers to convert measured values from 60 to 50 Hz and vice versa. Conversion factors are necessary when equipment at a manufacturer's test facility allows direct measurement at one frequency and not the other. These factors are developed for no load loss, exciting current, load loss, and noise level using both analytical and actual tested data. Measured data, provided by several manufacturers, was used to confirm the theoretical results. This paper will be used as a basis for proposing standard frequency conversion factors in the IEEE/ANSI and IEC test standards for power and distribution transformers. Such a standard will make it possible for manufacturers to use the same frequency conversion factors and hence have a more uniform accuracy of the reported test data at both 50 and 60Hz. Keywords: Curved conductor, heavy current, surface temperature, current conducting ability. Preprint Order Number: PE-106PRD (06-2002) Discussion Deadline: November 2002

Rezaei-Zare, A.; Faiz, J.; Mohseni, H. Author Affiliation: University of Tehran. Abstract: High power variable transformers are required for use in advanced high voltage - high power laboratories. However, their design is always confronted with various difficulties caused by different physical and electromagnetic design constraints. This paper presents a new design for a high power brushless linear variable transformer. The proposed design has desirable features such as low short circuit impedance which may be useful for different tests particularly high current tests, over a wide range of power requirement. An analytical design procedure is followed, after which a finite element analysis is used to confirm the analytical design results.

A Wide-Band Lumped Circuit Model of Eddy Current Losses in a Coil with a Coaxial Insulation System and a Stranded Conductor Holmberg, Par; Leijon, Mats; Wass, Torbjorn Author Affiliation: Uppsala University; ABB Corporate Research. Abstract: This paper presents a wide-band lumped circuit model of eddy current losses in a coaxially insulated coil. The wide frequency range of the model is achieved by means of dual and extended Cauer circuits, equivalent circuits used for eddy current modeling. The complete lumped circuit reproduces the expected response well. However,

vibration data from healthy and defective circuit breakers into wavelet features. Selected features highlighting the differences between healthy and faulty condition are processed by a back-propagation neural network for classification. Testing has been done for three 66 kV circuit breakers with simulated faults. Detection accuracy is shown to be far better than other classical techniques such as the windowed Fourier transform, stand alone artificial neural networks or expert system. The accuracy of detection for some faults can be as high as 100%. Keywords: Wavelet transforms, neural networks, vibrations, transient analysis, monitoring, circuit breakers. Preprint Order Number: PE-052PRD (06-2002) Discussion Deadline: November 2002

Transformers

IEEE Power Engineering Review,

September 2002

61