Modelling And Simulation Analysis On Distribution Transformer Under Lightning Stroke

Distribution network plays an important role in modern power system, and is a key aspect to ensure power supply reliability and power quality. According to survey, over 95% power failures in whole power grid were caused by distribution network faults. And almost half of power loss of the whole grid happens in distribution network. Besides, because of the complex construction and poor insulation, lOkV level distribution network is threated by lightning strikes. As the terminal equipment of distribution network, large amount of distribution transformers are connected with power users and are easily stroke by lighting. Therefore, distribution transformer’s lighting protection is necessary to safe power consuming. This paper’s works include following aspects:Equivalent wide bandwidth distribution transformer model which is suitable for lightning stroke is established including following parts:inductance which can react to overvoltage transfer relationship in low frequency band, stray capacitance which can present overvoltage capacitive coupling relationship in high frequency band, and resistance which can present power loss. The paper calculates these parameters and proves the correctness through simulation.Usually, lightning faults include direct lightning stroke and induction lightning stroke. To simulate direct lighting stroke, current lighting model is established; To simulate induction lighting stroke, voltage lighting model is established using controlled current source.Basing equivalent wide bandwidth distribution transformer model, direct lightning stroke simulation and induction lightning stroke simulation of distribution transformer, using PSCAD/EMTDC and MATLAB, are carried on respectively. After that, primary side’s voltage and secondary side’s voltage can be analyzed in time domain and frequency domain. At last, by analyzing the overvoltage inside distribution transformer, the poorest insulation point in distribution transformer can be obtained.According to different conditions, which are distribution transformer with arrester only installed in high voltage side and installed in both high and low voltage side, the overvoltage inside and outside distribution transformer have been obtained by simulation respectively.At last, the lightning stroke simulation is carried on at Beimen I line distribution area. The paper analyzes the overvoltage of both sides of distribution transformer and the overvoltage inside distribution transformer. Meanwhile, the overvoltage data of 38 monitoring points is recorded, and by comparing every overvoltage amplitude of each point under different lightning stroke, dangerous points in this system have been found out, then some warning measures have been proposed, too.