Owing to the uncertainty of sampling value(SV)packet transmission delay in switches

sampling synchronization is mainly achieved by the unified synchronous clock in the smart substation

resulting in network synchronization heavily dependent on the external clock. It also violates the basic principles of protection not relying on external synchronization system. Sampling synchronization technology is the key to whether the network sampling mode can really be practical and whether the network structure of smart substation can be greatly simplified if the sampling synchronization problem is to be well resolved. This paper gives a detailed analysis of the advantages and disadvantages of various sampling methods and puts forward a new type of synchronous sampling principle based on delay measurement of switch data transmission. The principle is simple and reliable; the correctness check of delay measurement of the switches can be achieved by evaluating the rationality of the equivalent merging unit data receiving time. The scheme has very good promotion prospects.