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VLD
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Voltage Limiting Device

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VOLTAGE LIMITING DEVICE In DC traction systems, potentially fatal touch voltages may occur between the return circuit and the earth structure due to operational currents and short-circuit currents. VOLTAGE HAZARD In such cases, a short-circuit device must be used as a voltage limiting device between the return circuit and the earth structure in order to prevent the presence of dangerous touch voltages. RUNNING RAIL EARTH General The Voltage Limiting Device (VLD) fulfills all the criteria of EN50122-1 standards. The VLD is used for: Protection of personnel Prevention of unacceptable voltage...

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• Basic VLD with contactor: VLD-B 3 VM: Sécheron voltage measuring amplifier 4 MIU: Sécheron current measuring amplifier A Earth B Negative Customer benefits: • Cost efficient • Simple installation through compact design • No commissioning required as the system is supplied ready for operation • Hybrid VLD with contactor and thyristor: VLD-H 1 Earthing contactor 2 SEPCOS: Sécheron protection and control unit 3 Trigger board 4 Anti-parallel thyristor 5 VM: Sécheron voltage measuring amplifier 6 MIU: Sécheron current measuring amplifier 7 Limiting resistor Customer benefits: • Low maintenance...

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Operation VLD-B: Protection functions: 1. Closing of the contactor in case of Umax - or Umax + detection 2. Control of the current value during 120s - If I < 40 A during 7s: Re-opening - If I > 40 A after 120s: Lockout (permanently in closed status and only resettable by manual operation) Closing of the contactor and lockout in case of Umax -- or Umax ++ detection This protection prevents continuous repetition of the sequence of closing and opening in case of fault protection followed by an automatic re-opening. The number of automatic re-opening is fixed to 3. The counter of re-opening is...

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