| Affected by freezing weather,the transmission line is seriously covered with ice,which has caused great harm to social stability and national economy.PST is used for line ice melting because of the power flow regulation of phase shifting transformer(PST).However,PST access will change the distribution of line voltage,current and impedance and increase the line elements,which are the important basis for the configuration and setting of relay protection.In order to ensure the safe and reliable operation of the PST system with melting ice,this paper will study the influence of PST access on relay protection.Firstly,the compensation mode,phase angle adjustment mode and main structure of PST are studied.The PST series access line with symmetrical double core structure is selected for ice melting.In order to understand the control and protection system of PST,the circuit structure and operation mode of the ice melting PST system are designed.Secondly,in order to analyze the influence of PST on relay protection,the configuration schemes of line protection,bus protection and transformer protection are studied,and the corresponding simulation models are built.In order to realize the dynamic simulation test detection of protection configuration,a power system relay protection experimental platform based on hardware in the loop simulation is designed.Based on the test examples and projects specified in gb/t 26864-2011,the rationality and integrity of the protection configuration scheme are tested by using the experimental platform.Then,the paper analyzes the mechanism of PST access to relay protection.For line zero sequence current protection,through analyzing the zero sequence characteristics of PST,it reveals that PST is equivalent to a constant resistance sensitive element in zero sequence network.For the line longitudinal current differential protection,according to the structure of PST,the phase shifting characteristics and superposition theorem of PST to each sequence network fault component,combined with the protection logic algorithm of zero sequence current differential protection,steady-state split phase current differential protection and split phase sudden variable current differential protection in line pilot protection,the mechanism of PST access to the action characteristics of line longitudinal protection is analyzed.For line distance protection,according to the phase-shifting characteristics of PST to the fault components and the equivalent impedance of each sequence network of PST,the influence of PST access to grounding and phase to phase impedance measurement algorithm is analyzed.For the automatic reclosing,in order to analyze the influence of PST access on reclosing,the coordination and cooperation relationship between the automatic reclosing and line protection,PST body protection and breaker state are studied.For bus protection and transformer protection,it is found that the influence of PST access on them is related to the installation position of voltage transformer and current transformer which provide protection electrical information.The correctness of the theoretical analysis is verified by simulation analysis.Finally,according to the influence of PST on relay protection,combined with the influence mechanism of PST and the actual engineering situation,the improvement measures of zero sequence current protection,current differential protection,distance protection and automatic reclosing are proposed.At the same time,the effectiveness of the improvement measures is verified by simulation analysis. |
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