Investigation Into Fault Analysis And Some Problems On Dc Traction Power Supply System For Urban Railway Transit System

With the improvement of the economic and enlargement of city scale, the construction of urban railway transit system in many metropolises has been on schedule. Safe and reliable operation of DC traction power supply system are the basis of whole urban railway transit system, it is very important to do research work on DC traction power supply system fault analysis, protection and relative problems.- The rectifiers are the key points of DC traction power supply system. The model construction and analysis of rectifiers are the basis of DC traction power supply system fault analysis. The tensor analysis has been utilized to simulate the rectifier operation. In this paper, the operation characteristic of the 6-pulse and parallel 12-pulse bridge rectifier, and the effects of the parameters of AC and DC system on DC fault transient have been analyzed in detail.- The third rail and running rails impedance model is very important for DC fault transient analysis, because of them used to feed / return the current from moving vehicles to rectifier substation. The steel rails are very susceptible to skin effect and saturation because they are large, magnetic conductors. The nonlinear magnetic characteristic of the steel complicates the current waveform because the increase in impedance due to skin effect is a function of the conductor permeability, which in turn is dependent on current. In this paper, the equivalent solid cylinder model of the rails according to the equal perimeter principle has been proposed, and a technique for calculating the fault current / time profile for DC traction power grid has been presented. Traditionally, a single value of resistance either measured at DC or at power frequency has been used with a single value of inductance, for calculating the current / time short circuit fault profile. With a comparison between a calculating profile and practically measured results obtained on a metro system, it is shown the technique presented in this paper is demonstrated to be accurate, and it is also shown the method based on DC resistance / power frequency inductance is not allowed to calculate the fault transient current profile.- It is becoming more difficult to detect the remote short circuit faults of DC traction power supply grid, particularly high impedance faults and arcing faults. The principles based on increment of current and rate of rise of current have been analyzed, and the mechanism of charging current has been investigated deeply when train crosses the power-off area. A new method based on charging current block has been proposed, which deals with the protection nuisance trips when the train crosses the power-off area, and a new principle, based on the rate of rise of current / increment of current and the voltage mutation detection, has been presented to identify the faults which happen in charging current block. When the arcing faults occur, the disturbance lowers the sensitivity of the rate of rise of current, so the principle based on timed increment of current has been presented. A new integrated relay was developed and passed the experiment on spot. The results show that the protection device can reliably and sensitively detect short circuit faults.- It is necessary to design a good digital filter when the relay is developed. Because the traction current signal contains a plenty of harmonic noise, they make a great influence on relay. In this paper, a new integration digital filter, based on multi sampling theory, has been presented, which can erase the harmonic noise effectively.