Research On New Problems Of Safe Operation In Active Distribution Network

In the active power distribution network,when the workers are in the maintenance work,the wrong power transmission happens suddenly,which will lead to the ground short circuit fault,which will also have some impact on the personal safety of the workers.However,at present,there are few reports on the quantitative research on the safe operation of active distribution network.In this thesis,10 k V distribution network was selected as the research object,and the grounding resistances of soil were obtained through experiments,and the correctness of soil model parameters was verified.Combined with MATLAB/Simulink and Comsol simulation software and contact voltage experiment,the short circuit fault and safe operation of active distribution network were studied.Firstly,the short-circuit fault analysis and safe operation of active distribution network were theoretically analyzed.The calculation method of ground current in safe operation of distribution network was not only introduced,but also compared with the traditional calculation method.The calculation methods of two indexes of safe operation-contact voltage and step voltage were also introduced.Then,through the joint simulation of MATLAB/Simulink and Comsol,the influences of buried depth of grounding electrode,soil type,neutral grounding mode and distributed power type on safe operation indexes(contact voltage and step voltage)were studied.After comprehensive analysis,it was found that neutral grounding mode without grounding and grounding through arc suppression coil is the safest for maintenance personnel,while three-phase closing power transmission mode is the best way for low resistance grounding system.In the neutral point through the small resistance grounding system using single-phase power transmission conditions,the deeper the buried depth of the grounding electrode,the greater the influence of the second moist soil.When the buried depth is 0.8 m,the contact voltage can be within safe voltage(36V),as long as the grounding point is less than 1.6 cm away from people and people does not touch the grounding wire.The type of soil and the access of distributed generation have relatively little influence on contact voltage and step voltage.The reason why distributed generation has little influence on contact voltage and step voltage is further explored,it is mainly related to the contact resistance of grounding device.In the case of single-phase power transmission,even if the penetration rate reaches 75% while the contact resistance is 0.015Ω,the short-circuit current of ground fault increases by only0.36%,compared with the distribution network without distributed generation.When the contact resistance is 1Ω,the short-circuit current of ground fault increases by 10.6%.Finally,the Back Propagation(BP)network algorithm was used to learn and train 630 samples with 10 attributes,such as voltage level of distribution transformer,neutral grounding resistance,load power,type and capacity of distributed generation,and a dynamic BP structure was proposed to adapt to the variability of structural parameters of active distribution network.It is of practical significance to build a safety operation data prediction platform to invoke and predict the model,to realize better human machine interface,and to facilitate the maintenance personnel to conduct safety check on site.