Study On Novel Protection And Location Schemes For Traction Power Supply System

With the development of electrified railway in our country and the construstion of high-speed railway (HSR) and dedicated passenger line (DPL), the protection and control for traction power system becomes important safety guarantee increasingly. There are several power supply modes, such as direct power supply mode, boost-transformer (BT) power supply mode and auto-transformer (AT) power supply mode. Series compesators are added in some direct power supply system, so the power supply capability can be enhanced. There are single-track-line and double-track-line mode in these power supply modes. The double-track-lines with parallel connections are on a large scale applied to AT power supply system in the HSR and DPL in our country.In our country, the direct power supply mode and AT power supply mode are mostly applied to traction power supply system, which is the research object, and research directions are following:AT substation were reconstructed or constructed in some railways, and Scott transformers were adopted. According to the current transform relation, three differential protective equations of the Scott transformer are proposed. It shows that three kinds of equations can operate correctly under all possible situations. By means of comparison of the influence of inrush current, sensitivity of protection and setting of three equations, it shows that the strongpoint and disadvantage of three wiring of current transformer (CT). The third differential protection scheme applied in Japan early can operates by phase respectably. It is better than others in reliability and sensitivity when correct operation guaranteed.The mal-operation of differential protection for traction transformer is easily caused by CT transient saturation. According to the CT connection and the variational quantity characteristic of differential current and restraint current, when inside or outside fault occurs, a new criterion to recognize CT transient saturation is proposed based on that the variational quantity sum of differential current and restraint current of three phases.Wrong-phase-coupling fault in the power traction system is one kind of normal short circuit faults. The current fault component waveforms of two phases are symmetrical based on the analysis of wrong-phase-coupling. This characteristic can be acquired by correlation analysis. According to the characteristic of power traction system, a new protective scheme is established based on the correlation analysis of fault component.When fault occurs on power supply system with series-wound compesators sets, there is more than one fault point corresponding to one reactance based on the reactance-distance table. A method to identify the fault is before or behind series-wound compensators is proposed based on the R-L-C model. Based on the mathematical morphology, the identified principle of detecting the short circuit of the discharge gap is proposed.The series-wound reactor on shunt compesators is short of necessary protection, especially the one against inter-turn fault. Based on the analysis of this kind of fault and its impedance characteristic, together with the particularity of power system in electrified railway, a new protection against inter-turn fault is proposed based on the measured impedance or the ratio of reactor voltage and bus voltage.Acorrding to the characteristic of AT power supply system with parallel connections, based on the generalized method of symmetrical components, the calculating method of impedance of this power supply mode is proposed. It is illuminated that fault location with reactance method is invalid.The fault location principle based on the ratio of boosting currents of ATs is still valid in this power supply mode and the principle is analysied and simulated. Based on the generalized method of symmetrical components model, the principle of ratio between upper line current and down line current and parallel line currents ratio were proposed. The two principles are compared to boosting currents ratio of ATs. It showes that the location principle based on parallel line currents ratio is better.