Wyniki 1-4 spośród 4 dla zapytania: authorDesc:"Muqing LIU"

The Application of Partial Discharge Detection for the condition assessment of XLPE Power Cables

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Partial discharge (PD) detection is an important means in the condition-based maintenance of high voltage apparatus including crosslinked polyethylene (XLPE) power cables. In this contribution, we introduce the recent work in Shanghai municipal electric power company on the condition-based maintenance of XLPE power cables. As to how to carry out the PD detection in different circumstances, three schemes are laid out in brief. Particularly, a novel idea of partial discharge joint detection method, which is based on multiple sensors, or the high frequency current transformer (HFCT) coupling technique, ultra high frequency (UHF) and acoustics emission (AE) partial discharge detection technique, is proposed. Use more than one kind of coupling techniques, the reliability of onsite PD detection and diagnosis can be improved significantly. Streszczenie. Przedstawiono metody wykorzystania wyładowania niezupełnego do testowania stanu kabli typu XLPE. Wykorzystano różne czujniki, jak np. wysokoczęstotliwościowy transformatorowy czujnik prądu czy czujniki emisji akustycznej. (Metody wykorzystania wyładowania niezupełnego do testowania stanu kabli typu XLPE) Keywords: XLPE cable; Partial discharge; Condition-Based Maintenance; HFCT; UHF; AE Słowa kluczowe: kable XLPE, wyładowanie niezupełne, testowanie stanu kabli 1 Introduction XLPE power cables play a significant role in the urban power network. The safe operation is vital to the stability for power grid. Once the cables break down, power failure will occur immediately. From the field photos, samples of failure cables and domestic major cities’ power cable repairing records in China, we found that there were certain causes for the failures of power cables, comprising external force destruction, intrinsic defect of cable accessories, quality problems of cable laying and cable production. The corresponding proportion was 58%, 27%, 12% and 3% respectively. High frequency current transformer[...]

Study on the driving circuit for LED Taxiway Centreline Light

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Light Emitting Diodes (LEDs) are suitable candidate for using in Taxiway Centreline light due to their inherent advantages such as high efficacy, long life time, and small package. LEDs can not directly replace the traditional halogen lamps used in airport because the power supply in the airport is a specially made AC constant current source. This paper designed a driving circuit for LED taxiway centreline light, which can be dimming, to ensure that LEDs can work stably in airport light. Streszczenie. Diody LED są dobrym kandydatem na światła ostrzegawcze dzięki dużej skuteczności, małym wymiarom i długiej żywotności. Nie zastąpi one świateł halogenowych używanych na lotniskach ponieważ zasilanie na lotniskach jest typu AC. W artykule przedstawiono układ zasilania diod LED umożliwiający zmianę jasności przez co mogą pracować stabilnie w świetle lotniska. (Analiza układu zasilania diod LED stosowanych do oznaczania drogi kołowania na lotniskach) Keywords: LED, Taxiway Centreline Light, Driving Circuit, Power Factor Correction Słowa kluczowe: LED, oświetlenie lotniska. 1 Introduction Taxiway Centerline Lights are used to facilitate aircraft guidance between the runway and apron area during low visibility operations. Taxiway Centerline Lights are recommended for use when visibility is less than 350 meters Runway Visual Range (RVR), but may be used under better visibility conditions in apron areas to assist parking operations[1,2]. Taxiway Centerline lights are embedded into the surface of the taxiway centerline with longitudinal spacing 15 m. They play a vital role in helping the pilot locate the exact location of the runway and know exactly where to touch the plane down. Fig.1 shows the intensity distribution for taxiway centerline lights. Fig.1. Intensity distribution for taxiway centreline lights Currenly, halogen lamps are widely used in Taxiway Centerline Lights. There are some disadvantages for these traditinal lamps: 1) Big p[...]

Improved Electrical Measurement Method for Junction Temperature of Light Emitting Diodes

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The electrical test method (ETM) is used to measure the junction temperature Tj of high brightness LEDs. NI 5922 digitizer and Keithley S2400 source meter were used to build the measurement system. Various measurement currents were used under 1MHz sampling rate. Results of different measurement currents are found to be the same under the same sampling rate and measurement error can be found under low sampling rates. When sampling rate is down to 0.2kHz, measurement error is up to 13.7%. Streszczenie. Zaproponowano metodę pomiaru temperatury złącza diody LED. Określono błąd metody dla różnych częstotliwości próbkowania. (Ulepszona metoda pomiaru temperatury złącza diody LED) Keywords: LED; junction temperature; electrical measurement; sampling rate Słowa kluczowe: diode LED, temperature złącza. Introduction As predicted by Hatiz’s Law, the lm/lamp of white LED increases 20 times per decade and dollar/lm of white LED falls 10 times per decade [1]. From the world first 1W white power LED LUMILEDS Luxoen I fewer 20 lm/W released in 1999 to the highest lumen efficacy commercial available LED CREE XP-G series max to 132lm/W at cool white today, great breakthrough has been made due to the development of AlInGaN chip manufacture technology, phosphor system and device structure [2]. The improvement of white LED’s lumen efficacy and LED’s long life time have made LED a competitive green light source for general lighting. However as LED is a semiconductor device, these two advantages of LED greatly depend on temperature [3]. Although LED is known as a highly energy efficient light source, there’re still about 2/3 of the input electric energy wasted and finally transferred into heat today. So thermal management of the LED system has always been and will remain the most critical issue in the near future. The junction temperature Tj of LED is the temperature of LED’s active layer where carrier injection and phot[...]

EMC Requirements and Test Methods for Light Emitting Diodes

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EMC test is important for the reliability improvement of LEDs and their application products. This paper introduces the EMC requirements for LED chips, LED devices and LED application products, focusing on electrostatic discharge, electrical fast transient, thunder stroke surge, voltage dip, conductive interference and radio frequency interference. Corresponding test methods are also given. These EMC requirements and test methods are valuable for LED manufacturer and end users. Streszczenie: W artykule przedstawiono wymagania EMC w stosunku do LEDów oraz urządzeń z nimi współpracujących, takich jak wyładowania elektrostatyczne, stany przejściowe, skoki napięcia, interferencje. Przedstawiono odpowiednie metody badawcze. (Wymagania elektrokompatybilności i metody badania układów LED) Keywords: LED; EMC; EMI; EMS; test method Słowa kluczowe: diody LED, kompatybilność elektromagnetyczna Introduction During the research or the manufacture of the LED (Light Emitting Diode) should be familiar with the phenomenon as followings: LED chips or the LED will go wrong and don’t work after they have been touched during the transportation; the LED application products (such as LED lamps, LED display screen) will stop working suddenly and then go on working, in some serious conditions should restarted it and then it can function well; the outdoor using LED application products often burning out during the thunder stroke. The major reason isn't the poor in the reliability. For the LED chips or the LED devices is the weak in the static electric immunity. For the outdoor using LED products is the weak ability in bearing the high power pulse interference, when there is surge pulse in the circuit it will burning out. In summary all those are the EMC issues. Recently, the EMC (Electromagnetic Compatibility) test has been more and more widely used as an important way in improving the reliability of the LED by the international advanced rese[...]

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