Selecting a suitable controlling algorithm for a regulated electric drainage

Electric drainage is used to protect devices which are buried underground (such as piping) from the negative effects of DC electric traction induced stray currents. In places where stray currents leave the underground device and return into rails, they contribute to the corrosion of buried devices. Electric drainage is one of the possibilities to minimise these negative effects. Electric drainage is a conductive connection between the buried device and electric traction rails, which ensures that current does not flow from the device into the ground, but it flows through this connection instead. Currently, the most widely used type is regulated electric drainage. In most cases, current is regulated by pulse width modulation (PWM). When this modulation is used, the current flowing through the drainage contains harmonic components with different frequencies. Track circuits are often used on railways, as an important part of the track security system. For secure operation, it is necessary to make sure that frequencies generated by the drainage do not interfere with track circuits. This paper deals with the design of a regulated drainage control system, with regard to its compatibility with track circuits. The paper contains results of computer simulation, as well as those of on-site measurements carried out on a prototype installed on a tram track.