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 This paper introduces a new kind of variable polarity plasma arc welding (VPPAW) process in which plasma arc current of positive and negative half waves flows in separate paths. It can be used adequately for welding aluminum, magnesium and their alloys. Compared to the VPPAW in which plasma arc is supplied by one power source and current of positive and negative half waves shares the same path, the significant difference of this method is that the current of positive and negative half waves is... This paper introduces a new kind of variable polarity plasma arc welding (VPPAW) process in which plasma arc current of positive and negative half waves flows in separate paths. It can be used adequately for welding aluminum, magnesium and their alloys. Compared to the VPPAW in which plasma arc is supplied by one power source and current of positive and negative half waves shares the same path, the significant difference of this method is that the current of positive and negative half waves is supplied by two independent power sources. This method makes the current of plasma arc and pilot arc in negative half wave to flow in separate paths. This practice not only avoids the current instability caused by interference between plasma arc and pilot arc, but also makes the negative half wave current of the new method on weld formation. It is found that positive half wave is the main factor influencing the weld formation, while negative half wave has less effect on the weld formation, and its main function is cleaning the oxide film on the work surface.  介绍了一种适合于铝镁及其合金焊接的变极性等离子弧焊新技术．此技术与由一台逆变电源为主弧电流供电、主弧正负半波共享一个电流通道等离子弧的传统技术相比，最大的不同是主弧正负半波电流由２台直流电源供电，正负半波电流分别流经２个不同的电流通道，对工件（铝）实现了变极性电流焊接．它的负半波不仅避免了传统技术因主、维弧相互干涉而造成的电弧不稳定，而且具有可靠的阴极清理作用．正负半波对焊缝成形的对比实验表明，正半波对焊缝成形起决定性作用，而负半波的影响很小，主要作用是完成对工件氧化膜的清理．  A timed electricity pricing model for power corporation with independent power source such as independent power plant and pumped storage is proposed as the result of study on electricity price, which is based on timed electricity pricing form and marginal cost. In the model trading price and trading quantities of all operations are considered as model parameters, as well as operating income as model objects. At the same time, the response of user aroused by electricity price fluctuation, generation... A timed electricity pricing model for power corporation with independent power source such as independent power plant and pumped storage is proposed as the result of study on electricity price, which is based on timed electricity pricing form and marginal cost. In the model trading price and trading quantities of all operations are considered as model parameters, as well as operating income as model objects. At the same time, the response of user aroused by electricity price fluctuation, generation cost curve and unit parameters of independent power plant and pumped storage are considered as restriction. The simulation result indicates the model is reasonable and the algorithm is effective.  以电价为研究对象 ,针对带有独立电厂和抽水蓄能电厂等独立电源的电力公司 ,在综合分时电价形式和边际成本定价方法的基础上 ,提出了其相应的分时电价模型。模型以电力公司日运营收益最大为目标 ,考虑了用户对电价波动的响应以及独立电厂、抽水蓄能电厂的发电成本曲线和机组参数等约束条件。仿真结果表明了所建立的分时电价模型的合理性和算法的有效性  Regarding DC system,as an independent power source,it is not influeuced by generator auxiliary power and system operating mode.We demostrated DC system reliability to safty operation of power plant.It is the ensurement of power plant safty operating.  针对直流系统是一个独立的电源,它不受发电机、厂用电及系统运行方式的影响,结合安阳发电厂分析直流系统的运行方式、故障危害,说明直流系统可靠与否对发电厂的安全运行起着至关重要的作用,是发电厂安全运行的保证。  
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