| With the fast development of electrified railway, the safety and reliability requirements for traction power supply system have been improved. Taking traction power supply system as the subject to be studied, it is significantly important to research the protection principle of traction power supply system theoretically and systematically. At the same time, maloperation and refuse operation of traction power supply system occurs time to time. In order to reduce damage to electrical equipment, high-speed railway demands protection action as quickly as possible once faults occur. So a new algorithm is needed to reduce the operation time of relay protection based on current protection operation time so that faults can be quickly identified and protection can operate immediately, which can better satisfy the speed characteristic of relay protection.Mathematical morphology is another new digital signal processing tool following the wavelet analysis, and is also an important tool for analysis and description of geometric morphology. The biggest difference between mathematical morphology and other algorithms is that the signal waves analyzing and processing are completely going on in time domain, besides, the processing itself just depends on the local characteristics of signals. What is more, morphological transformation only includes addition, subtraction and comparison operation, therefore, the computing is simple and time delay is small, which has a great application prospect in relay protection field.First of all, the traction power supply system and the protection configuration are introduced. The composition of power supply system, power supply modes and connection forms of the traction power supply system are explained. Both transformer and feeder protection schemes are expounded and different protection principles are analyzed, which can lay a solid theoretical foundation for discussions towards protection problems of traction power supply. Furthermore, basic theories about mathematical morphology are introduced in detail, meanwhile, a new criteria for distinguishing faults is put forward according to practical waves the traction transformers record and the simulation results. In addition, voltages and currents edge detection is realized by extracting the sudden change moments of voltages and currents, which verifies that the decrease of voltage will be followed by sudden current increase in low voltage protection.Secondly, fundamental theories of longitudinal differential protection are interpreted, which points out the key problem of transformer protection is how to correctly identify magnetizing inrush current and internal faults current. Transformer inrush current and internal faults current can be recognized according to the current waveforms characteristics extracted using mathematical morphology gradients method. At first, asymmetric inrush current can be distinguished according to the peaks and bottoms of waveforms located through mathematical morphology, and then magnetizing inrush current and fault current can be distinguished by comparing internal fault current area with symmetrical inrush current area after morphological gradient transformation.Lastly, owing to traction transformer protection maloperation caused by CT transient saturation, it is concluded that asynchronous method can’t effectively identify the extra-regional fault by comparing stalling current change and differential current change. The principle of differential protection based on time difference method is expounded, and the interval from the sudden change of phase current to the occurrence of differential current can be used to identify internal faults. Through comparing faults occurrence time and differential current generation time detected by mathematical morphology, differential protection can be latched up effectively, which will successfully solve the problem of traction transformer differential protection misoperation caused by CT saturation. |
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