Study On Protective Relay Of Traction Power Supply Systems For High Speed Railways

Traction power supply system is the power source of Multi-Units (MU) trains of high-speed railway, and protective relaying system plays a key role in reliably supplying power to MU trains from traction power supply system. Owing to the differences in system structure, power supply modes and power loads, protective relaying principles in traction power supply system differs a lot from that in electric power system. Due to the applying of cross-coupling Auto-Transformer (AT) power supply, V/x connection transformer and some other new techniques and MU trains, the fault and load characteristics of high-speed railway power supply system are different from that of normal-speed railway power supply system. Under the background of railway operating distance increasing fast and high-speed railway techniques stepping abroad, it is crucial and necessary to the continuous study on traction power supply system and its protective relaying principles and scheme configuration, which has both practical significance and social economic value. Main works of this thesis are as follows:Fast intertripping protective principle is studied in which feeding section is taken as a unit. Owing to the applying of cross-coupling AT power supply mode, both up and down feeding sections will be tripped when a fault occurs in traction supply network, which does not meet requirements of selectivity and quickness. Through deducing the short circuit currents expressions and short circuit impedance expressions at Substation (SS), AT post (ATP) and Section Post (SP) in cross-coupling AT power supply mode, it is found that the magnitude and direction of the measured currents and impedance can identify the fault which is close to them. On the theoretical basis gained above, feeding section intertripping protective principles are presented based on current and impedance characteristics, and also setting equations of all criteria are given. The simulation results of every kind fault occurs in the traction supply network show that at least one protective element installed in SS, ATP, SP can trip and intertrip the faulted feeding section, the non-fault feeding section is reliably not to be isolated and supplying power continuously.Backup distance protection and overload protection of traction transformer are also studied. When fault happens in the traction power network, the influence of power source impedance and traction transformer impedance on bus bar voltage is analyzed. Owing to the use of 220kV power source and large-capacity traction transformer, low-voltage starting overcurrent protection of high-speed railway transformer cannot reliably backup the relays of traction supply network. it is put forward that distance relay could be used as backup protection of transformer, of which protection configuration and setting principles are also given. Regular phase-to-phase impedance and phase-to-ground impedance could not correctly reflect the impedance value from relay installment place of Scott transformer to fault point due to the existence of phase rotation of the currents and voltages between high voltage and low voltage sides. Backup protection impedance relay models which applied to Scott transformer are built on the basis of analyzing the influence of mutual inductor wiring on measured impedance. Simulation results show that when the measured impedance at both high voltage and low voltage sides are very different from that under normal working condition, which validate the effectiveness of distance backup relaying. As to the overload requirements and traction load characteristics of traction transformer, the disadvantages of definite time and inverse time overcurrent relays being used as overload protection of traction transformer are analyzed. Based on hot point differential calculation given in standard GB1094.7-2008 "oil immersed type electric transformer load guide", an overthermal protective principle is presented. The simulation results show that overthermal relay based on thermal model is more available to reflect the overload status of transformer which traction load fluctuates frequently.The instrument transformer supervision criterion of traction power supply system is researched. Traction power supply system is a single-phase system, in which the instrument transformer supervision criteria based on sequence component in electric power system could not be applied. The influence of a fault location on current and voltage values in SS and SP is analyzed, which show that the existing voltage instrument transformer supervision criteria could maloperate and block the relays in end-coupling power supply system and cross-coupling AT power supply system. A supervision criterion can be used both for voltage transformer and current transformer is presented based on the characteristic that the voltage changes synchronously with the current change when a fault happens, but not in instrument transformer fault condition. The simulation results show that the presented criterion can reliably reflect voltage transformer fault and current transformer fault.At last, feeding section intertripping protective principles based on current and impedance characteristics are planning to apply in digital substation automation testing system of mid-south railway. As to different working modes in cross-coupling AT power supply network, including normal power supply and emergency power supply, specialized protection configuration and setting calculation principles are given. A lot of testing results based on RTDS show the correctness of interipping protective principles.