Abstract
The location of ground faults in railway electric lines in 2 × 5 kV railway power supply systems is a difficult task. In both 1 × 25 kV and transmission power systems it is common practice to use distance protection relays to clear ground faults and localize their positions. However, in the particular case of this 2 × 25 kV system, due to the widespread use of autotransformers, the relation between the distance and the impedance seen by the distance protection relays is not linear and therefore the location is not accurate enough. This paper presents a simple and economical method to identify the subsection between autotransformers and the conductor (catenary or feeder) where the ground fault is happening. This method is based on the comparison of the angle between the current and the voltage of the positive terminal in each autotransformer. Consequently, after the identification of the subsection and the conductor with the ground defect, only the subsection where the ground fault is present will be quickly removed from service, with the minimum effect on rail traffic. This method has been validated through computer simulations and laboratory tests with positive results.
Highlights
High-speed trains demand a power of about 12–16 Messenger wire (MW) to be able to reach speeds over 300 km/h.The normal method to provide such high levels of power comprises two power supply conductors and a grounded return one, which is called a 2 × 25 kV traction system, there are other power supply systems with differently rated voltages [1].This power supply system has a positive conductor at 25 kV AC voltage with a positive polarity with respect to ground, and a negative voltage conductor at 25 kV AC voltage with a negative polarity with respect to ground
When the tripping command given by the protection relay P127 is in response to the currents provided by CT1C or CT2C, the output free of potential contact RLP1 or RLP2 is activated at the corresponding P127 protection relay
A new method for identification of the subsection and conductor with a ground fault has been presented in this paper
Summary
High-speed trains demand a power of about 12–16 MW to be able to reach speeds over 300 km/h. These protection relays are usually installed at the traction substations and measure the impedance as the ratio between the voltage of the catenary and the difference of the catenary and feeder currents Such traction power systems with ATSs (2 × 25 kV) do not make use of ground fault location based on the linear ratio between the impedance (Z) seen from the traction substation and the distance to the ground fault. When a ground fault happens, the distance protection relays register an impedance value lower than their settings values and a tripping command is released to the normally used double pole circuit-breakers in the substation, with a consequent interruption of the power supply in all subsections and ATS’s of the section with the defect. As this information is sent to the control centre immediately, automatic or manual decisions can be taken to restore the power supply to the subsections without any ground fault
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