This paper provides a new synchronization method named Multi-Node Echo Method (MNEM), which settles the problem of data/clock synchronization even with asymmetrical channels by relaying echo messages among multi-node loops. Based on MNEM, the paper further provides a method to detect symmetrical status of a communication network, a method to detect asymmetrical status of any channel in a communication network, and a method to calculate the sending and receiving delay values of any channel in a communication network, even when the channel is asymmetrical. The proposed synchronization method based on MNEM is independent of GPS, and is especially useful for line differential protection in power system. © 2011 IEEE.

A method based on three sequences is proposed for break-conductor fault analysis on double-circuit transmission lines. Considering possible different phenomena of the two circuits in real-world situation,the relationship of the three sequence networks and characteristics of the sequence electrical quantities are studied first. Then combining with the boundary conditions of the disconnected ports,a new approach for calculating the post-fault electric quantities is presented. In order to simplify calculation process and make the characteristics of fault sequence voltages and currents more intuitive,a method of interconnections of sequence networks is presented and drawings of interconnections of sequence networks for typical break conductor fault types are given. The method has a definite physical meaning and is simple in calculation. It can serve as a basic theoretical approach for studying fault transient process and protection action characteristic in open-phase operation state on double-circuit transmission lines.

It is difficult to make fault analysis on four-circuit transmission line on the same tower because of the complexity of its parameters. A ccording to the characteristic of practical tower structure and conductor distributing order, a n algorithm based on matrix transformation theory is put forward for decoupling the parameters of the line, which are transformed into one set of double equidirectional sequences and three sets of double opposite sequences. I t has a clear physical meaning and easy to calculate .A ccording to the decoupling algorithm, a method based on interconnection of sequence networks is put forward for fault analysis on four-circuit transmission line,and then interconnections of sequence networks for 4 typical fault types in one circuit line are presented.The method, considering the character of the sequence quality of four-circuit lines on the same tower, lays a theoretical foundation for the studies of new protection principle and setting scheme.Simulations on EMTDC verify the correctness of the approach. This work is supported by National Natural Science Foundation of China (No.50477037 and No.50607014).

For short circuit fault analysis on double-circuit transmission line, a method based on three sequences is put forward. Combining with the boundary conditions of fault, a new approach for calculating the faulty electric quantities is presented, and the interconnections of sequence networks of typical fault types are given. Because it keeps the independence of the two lines, it can serve as a basic theoretical approach for studying the process of fault inception, tripping and reclosing on double-circuit transmission lines with some special line construction modes such as different line parameters or voltage classes of the two circuits on the same tower. ©2010 State Grid Electric Power Research Institute Press.

The independent compensation schemes for dual lines have limited compensation degree,higher recovery voltage and difficult secondary arc elimination,for which,a shunt reactor compensation scheme for dual parallel transmission lines on the same tower is presented.The shunt reactor compensation degree under traditional compensation mode is analyzed and the range of neutral point small reactor and its selection are discussed.The integrated compensation scheme for dual parallel transmission lines is proposed based on the analysis of line recovery voltage.Theoretical analysis and simulation show that,the proposed method realizes the ideal compensation degree selection,decreases the recovery voltage of trip phase and speeds up arc elimination.The selection of shunt reactor parameters and the most withstand voltage calculation of neutral point small reactor are discussed for different compensation modes.

Based on the analysis of the transmission capability of double-circuit transmission lines on the same tower in fault states and unbalanced states using six-sequence component method,an optimal trip scheme for double-circuit transmission lines on the same tower is proposed.Compared to the traditional trip schemes,the proposed scheme has advantages on maintaining the system transmission capability,and restraining the unbalanced components injected into system.It is available to improve the system stability,and creates better operation conditions for auto-devices like auto-recloser.Dynamic simulation and BPA simulation have proven the conclusions.