Study On High Frequency Transient Overvoltage Of Medium Voltage Cable Collecting System In Offshore Wind Farm

With the exhaustion of non-renewable energy and the worsening of the environment,the advantages of new energy are constantly emerging.As a new type of energy,wind energy has a strong competitiveness in many renewable energy sources,and it has received extensive attention from researchers at home and abroad.The installed capacity of the wind turbine is increasing year by year,and the wind power generation has entered a rapid development stage,and it has become an important part of the power grid.Therefore,the stability and reliability of the wind power system in the process of operation can not be ignored.Since the wind farm consists of the middle and low voltage power system with low insulation strength,the existence of overvoltage will destroy the normal operation of the system and cause the insulation damage of the equipment.The study of the problems in onshore wind farms is relatively mature,but the transmission network of the offshore wind farm is fundamentally different from that of the onshore wind farms.Due to the particularity of the environment,a large number of cables are used as transmission lines for offshore wind farms.When a vacuum circuit breaker causes the fan to enter or exit the system,traveling wave will propagate in the cable and catadioptric phenomenon occurs,resulting in transient overvoltage in the system,resulting in insulation damage of power equipment.Firstly,the offshore wind farm operating over voltage generating mechanism and characteristics are described,and the system of the main power equipment model is built using the electromagnetic transient simulation software PSCAD/EMTDC,including vacuum breaker,cable and transformer,and establishes the system simulation model of offshore wind farm.The effects of closing mode,closing phase and two kinds of protective devices on overvoltage are simulated and analyzed.Finally,the simulation model is verified by the method of simulation test,and Some waveforms of switching overvoltage at different phases are collected,and the effect of closing phase on the amplitude and steepness of transient overvoltage is analyzed.The results show that the inhibition effect of RC snubbers on overvoltage is better than that of absorption capacitor,it can also reduce the vacuum circuit breaker restrike overvoltage frequency and amplitude and steepness of the overvoltage.At the same time,for the closing operation in the peak voltage,the overvoltage amplitude and steepness is highest,the pre-strikes the most obvious.The more closed to the zero voltage at the switching overvoltage,the amplitude and gradient of the response is low,the pre-strikes phenomenon is weak.