Study On Leakage Fault Detection And Diagnosis Of Variable Flow System In Branched Heat Supply Network

In recent years,with the implementation of metering heating,the user can control the indoor temperature according to their own needs.The active adjustment of the user and the full utilization of free heat change the flow of the system end and the network.The operation of heating system turns from constant flow to variable flow,which can greatly save the energy consumption of circulating pump.At present,the main research of heating pipe network leakage is focused on the constant flow system in China.The research of variable flow system is still not enough.Therefore,based on the establishment of the mathematical model,this paper studies the detection and diagnosis method of leakage fault in variable flow system of branch heating pipe network by theoretical calculation method.In this paper,the mathematical model of variable flow system which is controlled by near-end constant pressure control method was established based on the graph theory.The hydraulic condition of the system under different leakage conditions was simulated by using this model.It is found that,in the condition that the available pressure difference meets the requirements of the heat transfer stations,the inlet pressure and the available pressure difference of the heat transfer station are reduced when the water supply pipe of the network is leaked.But the outlet pressure is basically unchanged.And the greater of the leakage,or the leak point closer to the end of the transfer station,or the heat transfer station located farther away from the heat source,the greater the pressure reduction.The change of leakage does not affect the trend of pressure change,only to change its range.When the leakage increase to a certain value,some of the heat transfer station located in the downstream of the leak point will appear the phenomenon that the available pressure difference is insufficient.With the increase of leakage,the leak point is closer to the end,the number of heat transfer station which is lack of available pressure difference is bigger,the heat transfer station which is the largest increase of flow is closer to the heat source.When the water return pipe of the heating pipe network is leaked,the available pressure difference of heat transfer station is increase,the export pressure decreases.But the inlet pressure is basically the same.The change of the leakage does not affect the trend of pressure change,only change its range.According to the law of leakage conditions,this paper used the total supply pipe flow,the total return pipe flow and the sum of each heat transfer station’s flow as the detect parameters for judging whether the leakage occurs,and the inlet or outlet pressure of each heat transfer station,the change of each station’s supply pipe pressure as diagnostic parameters for judging the location of the leakage.The mathematical model of leak point positioning is established by pressure gradient theory.That established a leakage fault detection and diagnosis system for variable flow system of branch heating pipe networks.At the end of this paper,the program which can be used to detect and diagnose leak fault out line is written by Visual Basic6.0 and be verified its correctness.