In order to improve the reliability of a relay protection system based on a communication system

a synchronization method based on the compensation for transmission delay is studied to achieve synchronization of network sampling independent of an external clock. The transmission delay composition and its features are analyzed first. Then the method of measuring and recording the switching delay is presented

followed by the development of the switch model. A prototype of the switch with the functions of switching delay measuring and recording is also developed. An experimental and theoretical analysis is conducted to study the accuracy of the switching delay measurement

and the results show that the switch developed has fairly high switching delay measuring accuracy. The principle of synchronization of network sampling is then presented. With a bus protection system as an example

the application of network sampling synchronization is tested

which shows that the proposed method is capable of effectively achieving synchronization of network sampling in ensuring reliability of the relay protection system. This work is supported by National Natural Science Foundation of China (No. 51377026) and Guangdong Provincial Natural Science Foundation of China (No. S2013010012885).