Y. Du

Lightning data observed with lightning location system in Guang-Dong Province, China

This paper presents an investigation into cloud-to-ground lightning activity data collected by a lightning detection system in the Guang-Dong Province, the southernmost in China. Annual lightning days are acquired and ground flash density maps are constructed from the database, which contains the information of more than one million flashes. The lightning days are compared with annual thunderstorm days collected by the Guang-Dong Meteorological Agency, and a weak correlation is noted. The correlation between ground flash density and thunderstorm day is studied, and an empirical formula is presented. The relationship between transmission line faults and ground flash density is discussed in this paper too. It is noted that the correlation with the faults caused by lightning is relatively high. The correlation coefficient does not significantly vary with the threshold of discharge current set for constructing the map of revised ground flash density.

A lightning location system in China: its performances and applications

This paper describes the largest lightning location system in China-Guang Dong lightning location system (GDLLS), which only locates the electromagnetic fields radiated by individual return strokes in cloud-to-ground flashes. Using information gathered from 14 combined magnetic direction and time-of-arrival finder sensors, the GDLLS provides both real-time and historical lightning data to the electric utility industry. The real-time data include the time of lightning strokes, their location and polarity and an estimate of the peak current. In this paper, the performance of the GDLLS is addressed, including detection efficiency and location accuracy. The potential applications of lightning data collected by the GDLLS are discussed also for electric power utilities in the Guang Dong province.

Experimental and numerical evaluation of busbar trunking impedance

Abstract This paper reports on experimental and numerical evaluation of the impedance of busbar systems with ferromagnetic enclosures (trunking). A linear model is developed in which the ferromagnetic material is approximated by a ‘linear’ material with an ‘equivalent’ relative permeability. The validation of this linear model is carried out through laboratory measurements on a sample system, and a reasonable level of accuracy is demonstrated. With this model, system impedance can be computed by employing the BEM software. The impact of design parameters, such as relative permeability, separation of bars, trunking size, etc on system impedance is discussed. Finally, the impact of these parameters on magnetic shielding is presented for the comparison.

Using EMTP for evaluation of surge current distribution in metallic gridlike structures

This paper presents a study on the utilization of EMTP (EMTP used for this paper is GNU ATP/Mingw32 running in WINNT OS) in calculating the lightning current distribution in the metallic structure of a building. The structure is modeled as a network of /spl pi/-circuits and represented by three parameter matrices, [R], [L], and [C]. With the modifications in EMTP, EMTP can compute the current distribution in the structure in either frequency domain or time domain during a direct stroke to a structure or an indirect stroke near a structure. Subsequently, the impulsive magnetic filed inside the structure can be evaluated. The accuracy of this method is verified by a laboratory experiment. A 10 m/spl times/10 m/spl times/10 m structure is also constructed in the paper for the illustration of both lightning current and magnetic field evaluations. The results show that EMTP is capable of analyzing lightning currents in the metallic gridlike structure of a building.

Monitoring the competitiveness in the supply of low-voltage switchboards

This paper reports an innovative, scientific and yet practicable approach developed in assisting a large-scale high-rise residential building developer in Hong Kong for monitoring the competitiveness in the switchboard supply to her development projects. In this study, a pricing indicator was developed for monitoring whether the pricing levels charged to developer had attained a competitive level. Our results revealed that the pricing level charged to the developed was far from competitive, and the high cost was contributed by inadequate competitiveness in the switchboard supply as a result of the practice of including only a limited number of suppliers on the pre-qualification list. By relaxing the pre-qualification requirements, the pricing level dropped to a very competitive level after two additional suppliers being included on the list.

Harmonic characteristics, limits and design strategies for compliance in office buildings

In Hong Kong, the low voltage distribution system in multi-tenanted, high-rise, air-conditioned office buildings is a small-scale power system. The matter of harmonics in the system is of increasing concern. To avoid potential disputes or problems related to harmonics, it is necessary to clarify the responsibilities of all parties involved. This paper identifies harmonics requirements for the building operator. Two different types of points of common coupling (PCCs) are introduced. The IEEE harmonic limits at these PCCs are discussed and compared with harmonic data collected in buildings. It is found that harmonic distortion levels at the PCC exceed the limits in some cases. Strategies for harmonic compliance in office buildings are identified, especially those which can be adopted in design of electrical installations.