Research On Capacity Increase Of Power Transmission And Transformation Equipment Based On Reliability Of Composite Generation And Transmission System

In recent years,the total electricity consumption in China has shown a steady growth trend.Existing power systems are faced with the problem of insufficient transmission and transformation capacity.The construction of new power transmission and transformation equipment,on the one hand,is long-term planning and on the other hand requires a large amount of funds and land resources support.Therefore,it is a preferable solution to alleviate this problem that the objective and underutilized capacity of power transmission and transformation equipment is used to increase its capacity.At the same time,the capacity increase of power transmission and transformation equipment enables it to have stronger power transmission capability at the peak of power consumption and N-1 power grid fault,and reduces the amount load shedding to the users,thereby improving the reliability of the transmission system.Thus,based on the basic requirement of improving the reliability of composite generation and transmission system,this work studies the capacity increase of transmission lines and transformers,which are the key components of power transmission and transformation equipment in composite generation and transmission system.The main contents and innovations are as follows:(1)Static capacity increase of power transmission and transformation equipment based on time-varying constraints method is proposed.The heat transfer characteristics of transmission lines and transformers are analyzed based on heat transfer theory and their heat transfer agent models are established.Subsequently,the agent models are applied to the proposed capacity increase method,which does not need to add new monitoring equipment or retrofit existing equipment,and can realize the capacity increase of the power transmission and transformation equipment in a short time.The results show that this capacity increase method can reduce the amount of load shedding for users in the event of less serious system failure,thus improving the reliability of the composite generation and transmission system.(2)In order to study the dynamic capacity increase of power transmission and transformation equipment,a new method to stabilize time series is proposed.This method works for that variance of series is not proportional to the development of the series.The simulating models of the main meteorological conditions(ambient temperature,wind speed and sunshine intensity)affecting the capacity of power transmission and transformation equipment are established.The results show that the simulating models established in this work can better reflect the characteristics of the real meteorological state.(3)In order to improve the reliability of composite generation and transmission system,the decision-making of dynamic capacity increase of power transmission and transformation equipment is studied.Firstly,the mathematical model of dynamic capacity increase of power transmission and transformation equipment is deduced.Combined simulating models meteorology established in the part(2),two transmission lines and two transformers with the highest average load power are selected respectively to simulate the process of dynamic capacity increase.Finally,the reliability of the composite generation and transmission system is evaluated by the sequential Monte Carlo method.The results show that the equipment capacity increase for large average load power can significantly improve the reliability of the entire composite generation and transmission system.However,the capacity increase of power transmission and transformation equipment with small average load power may not improve the reliability of the power transmission system at all.In addition,the simulating models of meteorology in different locations have a significant impact on the dynamic capacity of transmission and transformation equipment.In summary,this work started from the point of view of improving the reliability of composite generation and transmission systems,and studied the capacity increase of power transmission and transformation equipment from the perspective of heat transfer characteristics.The research results obtained above can provide a theoretical basis for the static capacity increase method of power transmission and transformation equipment,and provide a reliable method for the decision-making of dynamic capacity increase.