Abstract

The fractional frequency transmission system (FFTS) is a very promising long-distance transmission approach, which uses lower frequency (50/3 Hz) to reduce the electrical length of the ac power line, and thus, its transmission capacity can be in creased several fold. This paper introduces the experimental installation of FFTS and primary experiment results. The experiment uses the phase-controlled cycloconverter as the frequency changer, stepping up 50/3 Hz electricity to 50 Hz electricity and supplying it to the utility grid. Thus, a new flexible ac transmission system device is successfully established in this experiment. The s\nchro-nizing process of 50/3 Hz transmission system with 50 Hz utility system is introduced in this paper. The experiment results show that a 1200 km/500 kV transmission line can transmit more than 2000 M\V electric power when employing the FFTS. The experiment also illustrates that there is no essential difficulty to realize FFTS in engineering practice

Increasing transmission distance and capacity is always the motivation to advance power industry technologic. In the history of the ac transmission system, increasing distance and capacity mainly depends on raising voltage le\el ol transmission lines. At present, the highest voltage level of the <K power transmission line in operation is 750 kV. To further upgrade, the voltage level encounters difficulties of material and environment issues.

The high-voltage direct current (HVDC) transmission that has no stability limit problem once became another approach to increasing electricity transmission capacity. However, the current converters at two ends of HVDC are very expensive In addition, up to now, the HVDC practices have been limited to the point-to-point transmission, It is still difficult to operate a mul-titerminal HVDC system. From lc)82 to 2003, the total HVDC transmission capacity in the world was only 70 GW
The flexible ac transmission system (FACTS) has IWJ used to improve power system performance and has become a \ei\ hot research held j2|. The FAC T^ exploits powei ciectionic techniques to regulate the parameters ol the ac i:ann : w n which can raise transmission capacity to some degree.

In 1994. we proposed a novel electricity transmit!-M; approach, the fractional frequency transmission system (I 1 IS). which uses lower frequency (50/> H/) to reduce the electrical length of the ac transmission line, and thus, its transmis-pacity can be increased several fold . The system especially suitable to transmit remote hydropower for de\ countries, such as China.

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