| In recent years,with the rapid development of power system,the scale of 10 kV distribution network has gradually increased,and the types and quantity of distribution equipment have increased greatly.10 kV distribution transformer,as the contact equipment between different voltage systems in the distribution network,is an important part of the distribution network.As the operation mode of distribution network system is easy to change due to load change and low-voltage side fault,10 kV distribution transformer,as an important terminal node of distribution network,often suffers from switching overvoltage impact caused by load mutation and no-load closing;at the same time,a large number of 10 kV distribution transformers are distributed outdoors,and the operation environment is bad,so it is easy to pass through 10 kV Transmission Lines in thunderstorm days Circuit conduction,suffered from lightning invasion,withstand lightning overvoltage impact.Most of the power supply areas of Chongqing Jiangjin power supply company of State Grid are located in mountainous and hilly areas.The soil composition in hilly area is complex,and the temperature difference in four seasons is large.In the ridge or gully,due to the long and narrow terrain,accompanied by strong wind all year round,frost is easy to form in winter.In hilly area,the operation environment of 10 kV distribution network and distribution transformer is quite bad.Especially in thunderstorm season,it is more and more common for 10 kV distribution transformer to be damaged due to voltage impact.In particular,the 10 kV Jinping distribution station area is located in the deep mountains and has a long power supply radius.According to the statistics of the dispatching center,the 10 kV distribution transformer has been burned for more than 10 times in recent three years,which has caused huge economic losses and seriously affected the reliability of power supply.Therefore,it is of great significance to study the transmission mechanism and influence of overvoltage impulse in 10 kV distribution transformer,and find protection methods to prevent transformer accidents.This paper mainly analyzes the electromagnetic transient coupling mechanism and frequency characteristics of overvoltage conduction in the transformer when the distribution transformer in the 10 kV Jinping distribution station area is subjected to overvoltage impact,and the corresponding protection methods are studied(1)The electromagnetic transient coupling mechanism and harmonic oscillation characteristics of different theoretical models of 10 kV distribution transformer are analyzed theoretically,including common transformer high-frequency electrostatic coupling model and low-frequency electromagnetic conversion coupling model.The correctness of the broadband equivalent model of distribution transformer considering the electromagnetic coupling characteristics of high and low frequency band is verified by field test and software simulation.The impact of transmission line corona on overvoltage waveform is analyzed,and a complete overvoltage simulation theoretical model of 10 kV Jinping area distribution network is established.(2)Based on the research of 10 kV distribution transformer model,aiming at the situation of switching overvoltage and lightning overvoltage in 10 kV distribution network,the impulse response and frequency characteristics of overvoltage in different transformer models are studied and simulated.According to the structure and parameters of the 10 kV Jinping area distribution network,the overvoltage simulation model of the substation area is built by using the software atp-emtp.The frequency characteristics of the overvoltage conducted to the low-voltage side of the transformer when the high-voltage side of the 10 kV distribution transformer is invaded by different frequencies of overvoltage is simulated and analyzed.The frequency applicable range of different transformer models is calculated,and the field test is verified Data and theoretical research results.(3)Based on the theory analysis of overvoltage electromagnetic coupling mechanism,frequency response characteristics,field test and software simulation results of distribution transformer broadband equivalent model,the overvoltage suppression protection method of installing lightning arrester at high and low voltage side,installing inductance at high voltage side and reducing grounding resistance is studied.According to the actual situation of 10 kV Jinping distribution station area,it is suggested to install lightning arresters at both high and low voltage sides and reduce grounding resistance to reduce transformer damage caused by lightning overvoltage.And the overall economic benefits of protective measures are briefly analyzed.. |
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