Implementation of low voltage compensation control in medium voltage distribution network

Abstract: Voltage is an important assessment criterion of power quality. The low voltage phenomena (LVP) frequently appeared in the power distribution network especially at the rural areas of China, which had been key technical problem to be solved by the local departments of State Grid Corporation of China (SGCC). However, LVP happened mostly at the end of the rural medium voltage distribution system in the peak season, by which the electric power consumption of farming and farmers were seriously affected, and also lay behind the development of agricultural economy.Insufficient primary voltage of the distribution transformer was the main cause of rural low voltage phenomena. Increasing rural substation sites or the conductor section could also improve the power quality, but the investment cycle was too long and the rate of return lower. It is not suitable for large-scale popularization and application in rural areas. The thesis presented a synthesized optimal dynamic compensation method for low voltage in the whole electric power line, which was adopted practically and led in Xifeng medium voltage distribution network of Liaoning. First, based on the line voltage-regulation theory with voltage regulator and the terminal voltage monitored by feeder terminal unit (FTU), the voltage level of the whole electric power line was up to the national criteria with the power on-load tapping voltage regulator controlled by the remote host computer. In the meantime, at the basis of reactive power flow of the head line, and with the constraint condition of voltage in the nodes of reactive power compensators installed, the reactive compensation commands were sent by the remote host computer. The total reactive power capacity was 440 kvar (kilovolt ampere reactive) in each node of compensators，in which 50 kvar was as static compensation and the other as dynamic separated into 4 groups. According to the output of reactive power tide at the transformer substation, 1 static and 4 set of dynamic capacitor banks were composed of 17 different combinations in every compensation node, which was optimized for grouping parallel capacitor switch by the remote host computer based on the principle of reactive balance. Finally the national supervision standards of reactive power dynamic balance were reached after above computerized dynamic adjusting measures taken in the whole experimental power grid. The experimental results showed that the line power factor increased to 0.99 from 0.97 under the maximum power flow after the synthesized compensation implementation, and 10KV line active power loss rate decreased by 6 percent compared with before, and distribution transformer primary qualified voltage rate rose to 100% from original 22%. In the paper, several theories and methods of wireless communication and computer control and line-automation were integrated into the practical application example of comprehensive voltage compensation, which effectively improved the voltage level and fluctuating range, the qualified voltage rate and the power loss rate in the rural low and medium voltage distribution network.It has good reference value of engineering. The proposed methods also come up with new solutions for the intelligent development of reactive power compensation of rural substation.