Study On Voltage Quality Of District Grid Containing Distributed Generation

In remote mountain areas even with abundant hydropower resources,there are power grids with generally longer power supply radii,and the developed small runoff hydropower stations are connected to the 10 k V main power lines in T-shape,which has brought a great impact on the voltage quality of the distribution network.This results in the overall overvoltage of the distribution network during the peak period of power generation,which halts the production of users,and even leads to the burning out of electrical equipment.Besides,the overall voltage of the distribution network is too low during the power generation trough,which seriously disturbs the normal life and production of users.As a consequence,there are extreme concerns of the power supply bureau about how to mitigate the voltage impact of small hydropower networks on the power grid as well as promote the voltage quality of users.In Baipenzhu mountain area of Huidong,small hydropower stations are sparsely connected to different power lines in T-shape,which has a serious effect on the power safety and power quality of the distribution network.Meanwhile,it gives rise to the difficulty of distribution network operation and line loss management.In order to solve this problem,the thesis firstly studies the large range voltage fluctuation mechanism and influencing factors of10 k V power lines in remote areas where there are dense small hydropower stations with large installed capacity.By means of the field research and modeling and simulation of power flow calculation,it aims at finding out the reasons why there is a periodic variation of voltage of three power lines in Baipenzhu area,that is,there is overtension in wet period and low tension voltage in drought period.What’s more,it tries to advance the power management of power lines,stagger the peak power,and device the in-situ relative power balance scheme such as strengthening network power management,staggering peak power and installing shunt capacitors and reactors,the reactive power regulation scheme with line bidirectional automatic voltage regulation and the power network optimization scheme of35 k V substations.Besides,the parameters are selected and verified on PSASP simulation platform.Based on reactive power balance princple,the analysis of the 35 k V substation optimization scheme is put great emphasis on.How to select the sites of 35 k V substations is a key problem.Considering technical guidance planning,power loss reduction and implementation feasibility,this thesis rationally selects the sites of 35 k V stations,so that the power line voltage level reaches the standard while the power supply stablity can be greatly increased and power loss decreased a lot.At the same time,to ensure that on the premise of improving power network voltage effectively and upgrading the power quality of users at the terminal of power lines in low voltage transformer area,it developes an auxiliary tool for rapid resolution of power supply radii,which helps managers analyze power supply situations of transformers,and thus rapidly screen the ones in need of renovation,for optimizing quality of power supply and fulfilling the requirement of energy conservation and loss reduction.In the end,this thesis puts forward the optimal comprehensive treatment scheme in Baipenzhu area by integrating the in-situ relative power balance scheme,the reactive power regulation scheme and the power network optimization scheme in place,and considering the stablity of power supply,power loss reduction and improvement of voltage quality: The bidirectional automatic voltage regulator（BSVR regulation range is ± 10%）is installed in the middle of Baipanzhu lines.Meanwhile,one group of shunt reactors（capacity: 0.5mvar +0.5mvar）are installed at segment#63 of Baima branch line and one group of shunt capacitors（capacity: 0.5mvar）at pole#47 of the main dam branch line.Xinan lines are divided into three sections by building a new 35 k V Xinfeng station and installing small capacity reactors on the new line under the condition that the transformer taps are adjusted to-5%.A set of shunt reactors（capacity: 2Mvar）are installed at pole#56 of Hengzhai branch line of Hengkeng lines.The optimal scheme was verified on Baipenzhu PSASP simulation platform,and the optimization effect completely met the system requirements.After the operation test of power supply bereau,the scheme has achieved a good effect on governance,which proves that the scheme is reasonable and feasible,and can provide a reference for constructing small hydropower stations in other areas.