| Transmission lines icing,as a common natural disaster in southern China,is extremely harmful to power grid security.Especially in the 2008 ice disaster,many transmission lines in the most of southern province of China suffered great damage,and huge economic losses resulted from it.Therefore transmission lines melt-icing technique is early focused and researched by electric research staff.Nowadays,the methods of AC and DC short-circuit deicing are widely used.However,the former is limited by reactive capacity of ice-melting power supply,so it’s right for 220 kV transmission lines and those below the voltage level,or the short power lines.And an expensive DC ice-melting power should be used in the latter,so it is not economic namely and is appropriate for high-voltage and long-distance transmission lines.The new high-frequency deicing method is more efficiency,especially with smaller deicing current needed and little power failure.But the related basic theory needs to be further researched,and the high-frequency excitation power supply device of melting ice also needs to be developed.For the problems to be researched urgently of high-frequency deicing method and the existing defects of AC short-circuit deicing method,this thesis studied the high frequency excitation melting ice method and the frequency resonance melting ice method,and made a comparison analysis.An depth research on transmission line deicing based on high frequency excitation is conducted at the first: based on establishing the physical model of melting ice under the high frequency condition and carrying on several kinds of connection mode of melting ice,how to select the optimal excitation frequency and voltage with considering the attenuation of melting ice power is presented.After choosing Sanxia-Wanxian 500 kV AC transmission line as the object of melting ice,the feasibility of melting ice with a high-frequency excitation power supply parameters for 3kHz/11 kV is researched.Above it,the AC-DC-AC three-phase voltage type inverter cascaded H bridge structure with CPS-SPWM control technique is proposed as high-frequency melting ice power solution,and it’s identified by MATLAB simulation.On the other hand,in order to solve the problem of AC shorted melting ice application limitation,a kind of frequency AC deicing method is proposed based on the principle of series resonance on the icing transmission line: thefundamental principle of the deicing method is analyzed,then the physical model of transmission line icing is built in this thesis.In view of several typical lines,the cases are analyzed.The feasibility of the deicing method is proved by analyzing the melting ice resonant voltage quantitatively.The preliminary design program is given,mainly for the frequency AC power of melting ice and series compensation equipment.At last,based on the above research,four typical transmission lines are considered as the research objections.The main technical indexes of high frequency excitation melting ice,frequency resonance deicing,and DC shorted deicing are analyzed and compared through ANSYS simulation.And the technical characteristics as well as applied scope of three deicing methods are obtained,for the purpose of laying the foundation of the practical application of the former two methods.The method which decides the optimal excitation frequency and voltage with considering the attenuation of melting ice power is more actual to reality in this thesis.And the high frequency power supply design can reliably output high frequency voltage with low harmonic content and switching loss.The frequency resonance deicing method firstly proposed solves the problem that conventional AC shorted deicing is required to provide an excessive reactive power.Meanwhile,the frequency power and even series compensation capacitors could be introduced from the power system.As a result,the cost of deicing is low and the problem of transmission line icing also could be solved effectively. |
PDF Full Text Request