Development of an advanced voltage control technique to improve voltage and reactive power characteristics of a large‐scale power cable system

Abstract

AbstractThe power supply system for a metropolitan area consists of multiple 275‐kV power cable systems to supply power to a large number of consumers. Each system has a large charging capacity (capacitive reactive power). When 275‐kV power cable systems experience a voltage drop, their charging capacity decreases. However, the reactive power losses increase in the 275‐kV overhead transmission lines, which supply large power to power cable systems, thus causing the performance of the power supply system to deteriorate.In this paper, the following three points are reported: When the secondary power system of the trunk substation is a large‐scale power cable system, new techniques can greatly improve the voltage and reactive power characteristics by controlling the rise of the sending‐end voltage at the secondary side of the trunk substations and maintaining the voltage of power cable systems at a constant level. In the use of this control technique, it has been demonstrated that controlling by the direct‐detecting method of a voltage drop in the primary power system is superior to one that controls by the indirect‐detecting method, which increases load power in the cable system. The results of simulations obtained by using a 275‐kV cable system model and a performance power system model show that the use of this control technique can produce a good effect despite the allowances made for the opposite effect, i.e., a decrease in the capacity of power capacitors resulting from voltage drop at the tertiary voltage of a 500‐kV transformer. This study is carried out to examine the possibility of lightning control using a photoionized plasma produced by a UV laser without an optical air breakdown. As the fundamental experiment, the characteristics of a laser‐triggered spark gap (LTSG) are examined, where a laser beam is not irradiated on the surface of the electrodes. In this experiment, the KrF excimer laser is very effective in increasing the plasma density ne and the reduction ratio p of 50 percent breakdown voltage against the self‐breakdown voltage. The relation between ne and p is increased by generating a long and high‐density plasma parallel to the discharge axis.On the other hand, the abnormal discharge process in triggered lightning using a rocket is examined, and it is indicated that the most important condition to trigger a lightning discharge is the production of a plasma channel of length 200 m and density about 1019 m−3. It is suggested that such a plasma channel could be produced by a KrF excimer laser with an energy of only about 3.67 J.