Description

Voltage relays for traction power supply systems

Whether during scheduled maintenance work on a traction power supply system or in an emergency – for example, if emergency services need to approach live parts of the system in the event of a fire – before anyone connects components or enters an area where operating voltage may be present, it must be established beyond any doubt that the system is actually de-energised. This verification is not optional, but follows the established electrical engineering safety principle of ‘verifying absence of voltage’ – one of the five safety rules for working on electrical installations – and is also firmly enshrined in railway-specific regulations for emergency situations: Even after a catenary has been switched off, residual voltage may still be present, which is why emergency procedures in the railway sector require a verified confirmation that the system is de-energised before staff or emergency services intervene. The WITT-TVM traction voltage relay handles this safety-critical monitoring entirely autonomously: It requires no external auxiliary voltage, but draws its power directly from the measurement voltage being monitored – this saves on cabling and installation work and reduces potential sources of error. As we configure each unit at the factory with up to eleven customer-specific threshold parameters, there is no need for time-consuming on-site commissioning; You receive a relay precisely tailored to your operational requirements rather than a standard product. Simply submit your enquiry via our online configurator; we carry out the parameterisation exclusively at the factory and then perform 100 per cent testing on every single unit – this rules out operator errors during configuration and ensures the maximum safety for life and limb that is essential when working in live electrical areas.

Benefits for the business

• Reliable during maintenance and in an emergency: a dependable indication that the circuit is de-energised – the fundamental safety principle on which railway-specific emergency procedures (e.g. in the event of a fire) are also based.
• No additional installation work required: self-powered from the measurement voltage; no external auxiliary voltage required.
• Reduced commissioning risk: Factory-set, customer-specific configuration of up to eleven threshold parameters instead of on-site programming.
• Operator error ruled out: As the parameters are set at the factory – rather than by on-site staff – the most common source of error in safety-critical configurations is eliminated.
• Tested safety: Every device undergoes a 100 per cent inspection before dispatch – ensuring maximum safety for life and limb in live electrical areas.
• High operational reliability: Designed to meet the most stringent safety requirements, with a breakdown voltage of up to 2,100 V DC/5 ms.
• Durable: Relay contacts rated for > 1,000,000 switching cycles.

Function of the TVM traction voltage relay

The WITT-TVM is an analogue voltage monitor designed to meet the most stringent safety requirements and, in functional terms, forms part of the safety system for protection against electric shock in fixed railway installations. It is connected directly to components carrying traction voltage, has a high dielectric strength for traction voltages (750 V/20 ms, 1,000 V/15 ms or 2,100 V/5 ms) and is powered entirely by the measured voltage – no external auxiliary voltage is required. Specialised signal filters ensure that even the pulsating traction voltage of a DC railway is correctly detected and analysed.

When the factory-set threshold values are reached (up to 11 parameters, including the switch-on threshold UTn > 250 V DC with a switch-on delay ta of 1–6 s and the switch-off threshold Uoff > 200 V DC with a switch-off delay tv of 0.1–2 s), the measuring unit activates two separate, potential-free changeover contacts (NC/NO) and signals when the value is exceeded or falls below the threshold via a separate signal contact in each case (signal duration Son/Soff 2–20 ms). A yellow LED indicates the switching status (ON/OFF).

Configuration & Quality Assurance

The customer submits their configuration request via the online configurator: in it, they describe their application and the desired threshold values. The actual parameterisation of up to eleven threshold parameters is carried out exclusively by us at the factory – not by the customer on site. Every single device undergoes a 100 per cent inspection prior to dispatch. This procedure systematically rules out operator errors during configuration and ultimately serves one purpose: to ensure maximum safety of life and limb when working on or near live railway power supply systems.

For further information, see the configurator