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The VLD class 2.2 from Rudolf Waechter is a bipolar voltage limiter of the VLD-O (or VLD-O+F) type designed for DC and AC traction or their combinations. Its exceptional repeatable electric parameters predetermine it for all types of modern railways with powerful power stations and high operating and short-circuit currents. The VLD class 2.2 consists of a set of high-energy varistors connected in parallel with two antiparallel electronically controlled power thyristors. The role of the A2 varistors is to protect the surroundings as well as internal semiconductors of the VLD from pulse voltage (especially lightning strikes, etc.); with a short delay the thyristors then react to the impermissible touch voltage, which, by switching on, will establish an equipotential connection between the rail and the ground, thus protecting passengers (and the varistors from destruction). The reaction of the thyristors is set during assembling the control electronics and is two-stage. If the voltage potential at the VLD terminals exceeds the voltage limit UTi, the thyristor typically switches with a delay of 1ms. If the voltage potential is lower than UTi but at the same time higher than UTn, the thyristor response is typically 10ms. However, the voltage and time switching levels can be set to other values ​​according to the customer’s needs upon agreement during production (of course within the limits set by the EN 50122-1 standard). Bipolar VLD class 2.2 can be connected to the track via any terminal regardless of the traction polarity. The VLD body is manufactured by precise CNC milling in order to achieve exceptional electrical parameters. A special aluminium alloy is used for VLD body production, which is resistant to acidic and salty atmospheres. The voltage limiter is also equipped with sensors that monitor the maximum operating temperature of the thyristors and can be connected to a radio module that is capable of remotely indicating device overload. The main function of the VLD-O is to protect passengers, crews and technology from non-permissible touch voltage that may occur on the return conductor (rail) during normal train operation, especially at greater distances from substations (the reason is the higher voltage drop on a long return conductor). The exceptional repeatable electrical load parameters of the VLD Rudolf Waechter predetermine its use with advantage also as a repeatable VLD-F (i.e. in the VLD-O+F mode), which is a modern trend, because the VLD-O+F with sufficiently high repeatable loads minimizes the risk of fatal VLD failure during train operation and especially during OCL failure (short-circuit), which allows minimizing operating costs for periodic measurements and VLD replacements after fatal failures and, last but not least, optimizes the protection of the traction infrastructure against corrosion caused by stray current flow through damaged VLD. This effect can be further enhanced by remote wireless signalling of the VLD failure state thanks to integrated sensors connected to a wireless transmitter. The combination of our VLD class 2.2 with a voltage and current monitoring module and wireless remote data transmission often allows the replacement of significantly more expensive VLD class 4 on most traction sections. If you are not sure about the suitability of using class 2, please, contact our technical support. We will consider the situation together and recommend a suitable solution.