In recent years, with the rapid development of urban rail transit, Communication Based Train Control system is very important to improve the operation efficiency and ensure the traffic safety. Before urban rail transit lines are put into operation, they need to be tested strictly. In view of the lack of unified test standards, specifications and low test efficiency, a formal test sequence generation method for CBTC system is proposed. Firstly, the test line is divided into several test segments; secondly, analyze the constraint conditions of test cases and get the expression of constraint relationship of test cases; thirdly, analyze the characteristic quantity that can represent the line characteristics, and get the line characteristic expression; and then match test cases with test segments using matching algorithm; finally, concatenate test cases into test sequences using the concatenation algorithm. The results show that the test sequences generated by this method meets the test requirements of CBTC system. The test sequences cover all test cases. And the method can effectively improve the test efficiency.
The structure of conventional distribution system is radial, and overcurrent relays are widely used as primary protection. When a large number of distributed generations (DGs) are introduced, the system becomes an active distribution network. It is necessary to study new protection schemes applicable to active distribution network. This paper proposes a pilot protection scheme for active distribution network considering branches. The relationship of current phase variation direction and load power flow direction are used to build a criterion. Simulation results show the protection scheme can accurately identify the faults.
With increasing integration of distributed generation (DG) to the active distribution systems, the existing grid structure and protection configuration cannot meet the requirements of reliability. Adopting closed-loop configuration and reasonable protection schemes, it is possible to reduce the range of power outage and ensure continuous supply of DG. Firstly, an IED (intelligent electronic device) based complete protection structure consisting of several protection functions is proposed, including line protection, load protection and node protection. The protection principles of each protection function is described. The paper also studies the single-terminal weak-infeed issue of closed-loop distribution system by theoretical and simulation analysis. It is proved that the current phase variation based line protection function is not affected by the magnitude of fault current. It could correctly identify the fault under single-terminal weak-infeed condition.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.