Analysis of harmonic composition in electrical networks of step-down substations in coal mines

The integration of alternative energy sources and various technologies of distributed generation with power electronic converters in electrical networks leads to an increase in the diversity of the network, but at the same time to the tightening of the requirements of various standards, for exam-ple, a limited harmonic composition of the generated current, continuous operation of the device with voltage distortion, etc. Taking this fact into account, the paper presents the results of experi-mental studies of the effect of a hybrid inverter on power quality indicators at the point of common connection. A laboratory bench was developed. It consists of a three-phase hybrid inverter, a stor-age battery, a linear load in the form of an active resistance and a capacitor unit. The inverter has been connected to the power supply for parallel operation to supply the load in the form of active resistance. The modes of battery charging and power delivery to the network with two variations of the system resistance were investigated. The power output from the inverter varied from 500 W to 2 kW in the mode of generating electricity to the grid, and in the range from 50 to 300 W in the bat-tery charging mode. As a result of laboratory studies, the dependences of the total harmonic current distortion (THDI) were obtained for various operating modes of the inverter and system resistances. On the basis of the obtained results, an algorithm for the selection of methods and means to ensure electromagnetic compatibility during operation of the load and a hybrid inverter with energy storage was developed. It makes it possible to reduce the effect of hybrid inverters on the voltage distortion of the supply network.

Download Full-text

Rem Study of Current Effect on the Structure of Clean Si(111) Surface

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180288 ◽

1990 ◽

Vol 48 (1) ◽

pp. 306-307

Author(s):

A. Yamanaka ◽

H. Ohse ◽

K. Yagi

Keyword(s):

The Other ◽

Current Direction ◽

Clean Surface ◽

Current Effect ◽

Atomic Steps ◽

Step Bunching ◽

Terrace Width ◽

Step Down ◽

A Current

Recently current effects on clean and metal adsorbate surfaces have attracted much attention not only because of interesting phenomena but also because of practically importance in treatingclean and metal adsorbate surfaces [1-6]. In the former case, metals deposited migrate on the deposit depending on the current direction and a patch of the deposit expands on the clean surface [1]. The migration is closely related to the adsorbate structures and substrate structures including their anisotropy [2,7]. In the latter case, configurations of surface atomic steps depends on the current direction. In the case of Si(001) surface equally spaced array of monatom high steps along the [110] direction produces the 2x1 and 1x2 terraces. However, a relative terrace width of the two domain depends on the current direction; a step-up current widen terraces on which dimers are parallel to the current, while a step-down current widen the other terraces [3]. On (111) surface, a step-down current produces step bunching at temperatures between 1250-1350°C, while a step-up current produces step bunching at temperatures between 1050-1250°C [5].In the present paper, our REM observations on a current induced step bunching, started independently, are described.Our results are summarized as follows.(1) Above around 1000°C a step-up current induces step bunching. The phenomenon reverses around 1200 C; a step-down current induces step bunching. The observations agree with the previous reports [5].

Download Full-text