The Research On Type Design And Insulation Coordination Of Single Phase Parallel Gap For 10kV Overhead Transmission Lines

The reliable operation of 10 kV overhead lines directly affects the economic benefits and electricity consumption of the majority of users,while there are few lightning protection measures available for 10 kV distribution network.In the previous study,it is proposed that the single-phase installation method of parallel gap can effectively improve the lightning withstand level of 10 kV overhead bare wire line and reduce the lightning trip rate.However,after the installation of single-phase parallel gap,the single-phase grounding caused by gap discharge does not cause line tripping,resulting in power frequency continuation is not easy to extinguish,which affects the stability of the distribution network.At the same time,the insulation level difference between lines and equipment is further expanded after the single-phase installation of parallel gap,and the distribution equipment is more vulnerable to damage.Therefore,it is necessary to study the method of parallel gap with rapid arc extinguishing ability and adjusting the insulation level difference between lines and equipment.Based on the principle of magnetic fluid,considering the coupling effect of temperature,air conductivity and atmospheric pressure(such as thermal buoyancy),the motion simulation model of AC arc on parallel gap is established.Taking the parallel gap of 10 kV overhead transmission line as an example,the AC arc motion process is simulated.The calculation results show that the AC arc motion has the characteristics of ’zero break’,complex arc column bending,arc root jumping and different movement rates of upper and lower arc roots,which are consistent with the experimental results.Taking the movement rate of AC arc on the parallel gap and the time required for extinguishing non-reignition as indexes,the influence of different inclination angles of the guide arm on the arc motion law under 10 kV asymmetric rod-shaped parallel gap is calculated.It is concluded that the inclination angle structure of the lower guide arm at 45 °is the best,which provides methodological guidance for the design of parallel gap with rapid arc extinguishing function.Aiming at the problem that the insulation level difference between lines and equipment is further expanded and the distribution equipment is more likely to be damaged after the singlephase installation of 10 kV overhead lines with parallel gaps,this paper comprehensively analyzes the different ways to adjust the insulation level difference,and adopts the method of installing coupling ground wire at the end of 10 kV lines to solve this problem.The shunt principle of coupled ground wire is studied,and it is considered that the number of towers across and the grounding resistance of towers are the main factors affecting the shunt effect.Based on ATP-EMTP over-voltage calculation platform,the over-voltage simulation model of 10 kV overhead bare conductor line under the single-phase installation mode of parallel clearance is established.The calculation results show that in the typical configuration of 10 kV overhead line,when the induction point of the induced lightning is in the four base towers before the distribution transformer,the maximum over-current energy flowing through the MOA at the high voltage side of the distribution transformer exceeds the threshold value of its safe operation.At this time,the coupling ground wire is set up on the two base towers before the distribution transformer,and the tower grounding treatment is not required.The over-current amplitude and thermal charge transfer value flowing through the high-voltage side MOA can be limited to below the safety threshold,which are reduced by 69.4%and 83.5%,respectively.The proposed method plays an important role in reducing the failure rate of distribution equipment and adjusting the insulation level difference between lines and equipment.By designing the single-phase parallel gap with fast arc extinguishing characteristics and adjusting the insulation level difference between 10 kV overhead lines and equipment,it has important theoretical significance and practical engineering value for the distribution network to promote the use of single-phase parallel gap,reduce the lightning trip rate of 10 kV overhead lines and the failure rate of distribution equipment.