Load Management Optimization Strategy Of Buried Transformer Substations Considering Underground Heat Accumulative Effect

In the urban core areas where land resources are scarce and expensive,it is difficult to expand the distribution infrastructure,and the cost of power supply keeps rising.The emergence of buried substation effectively alleviates or completely solves the above problems.However,whether it is a direct-buried transformer substation(DBTS)or semiburied transformer substation(SBTS),the transformer is placed in an underground prefabricated confined space.Due to the difference in the thermodynamic and physical characteristics of the underground soil environment and the air environment around the traditional overground substation,it is easy to lead to the phenomenon that the power consumption heat of the substation accumulates in the surrounding soil during the external transfer,which will affect the temperature rise during the normal operation of the transformer.Under the background that DBTS have been widely used,it is of practical significance to study the influence of underground heat accumulation effect on the loss of life(LOL)assessment,capacity allocation and load management optimization of substations for the safety,stability and economic operation of distribution network.The study of this research is outlined follows:An extended thermal circuit model of a DBTS considering the underground heat accumulation effect is established,which improves the calculation accuracy of the hot spot temperature(HST)of the direct-buried transformer windings.Firstly,the soil thermodynamic properties are studied by the heat transfer theory,and the heat transfer process of the DBTS revealed.Secondly,based on the heat-electricity analogy,the heat flow exchange and energy balance process of the main equipment in the station,such as the transformer and the medium and low voltage distribution cabinet,is modeled by using the thermal circuit model method,and the transformer winding HST is obtained.On this basis,combined with the Arrhenius theory,a LOL assessment method suitable for DBTS is proposed.The case study results show that the underground heat accumulation effect makes the response of the HST to the load rate change have a significant thermal lag,and the proposed method effectively improves the accuracy of the transformer LOL assessment.An optimization model of DBTS capacity configuration considering the transformers LOL is constructed.Firstly,the actual power consumption behavior of an office building in Hunan Province is analyzed,and uses the life cycle cost method to configure the transformer capacity of the load.Based on the result,HST calculation and LOL assessment were carried out to study the influence of underground heat accumulation effect on transformer capacity configuration.On this basis,combined with the life cycle cost theory,construct a directburied transformer capacity configuration model considering the transformer LOL.The results show that the HST of the transformer with the optimal capacity selected by this model has smaller out-of-limit degree,shorter out-of-limit duration,and the annual average load rate is closer to the economic load rate.An optimization strategy for DBTS load management considering the access of distributed photovoltaic and energy storage systems(ESS)is proposed,which reduces the electricity cost of two-part electricity price users.Firstly,the influence of photovoltaic access on the utilization rate of transformer is analyzed,and the influence of ESS access on the energy consumption economy of two-part electricity price users and the system peak-valley difference are studied.The proposed load management optimization model considers that the energy storage system uses the peak-valley price difference and the peak-normal price difference to adjust its own charging and discharging strategy.The simulations indicate that the proposed optimization strategy can reduce the energy cost of users and improve the transformer utilization rate.In summary,this paper proposes a prefabricated DBTS load management optimization strategy that considers the underground heat accumulation effect,which improves the LOL assessment accuracy of the DBTS,reduces the energy cost of users.It provides theoretical reference for the load management optimization of the DBTS and the popularization of the two-part electricity price in the general industrial and commercial users.