WITT WB-CM 4 Cable Monitoring System for DC Cables

Description

Application of cable fault monitoring

A power cable failure incurs high costs and damages a company’s reputation. The WB-CM4 cable fault monitoring system continuously and autonomously monitors return conductors and power cables in DC cable systems, detecting cable faults at an early stage – before they lead to an operational outage or a safety risk. It thus makes a significant contribution to the operational safety and availability of cable systems, particularly in the catenary and power supply infrastructure of electrified railway lines.

In the case of monitoring shielded power cables, the WB-CM4 fulfils the requirements set out in VDV Publication 515, Issue 4/1993, for monitoring cables with a concentric shield or conductor and an insulating outer sheath.

Benefits for the business

• Greater availability: Damage caused by external factors or ageing cables is detected before it leads to unplanned outages.
• Lower maintenance costs: Continuous condition monitoring enables a targeted, predictive maintenance strategy rather than fixed inspection intervals.
• Enhanced security: Early fault detection reduces risks in critical infrastructure.
• Expandability: The system can be adapted in a modular fashion to meet future requirements using the optional WB-CM41 measurement channel and additional sensors for temperature and humidity.

Applications of cable monitoring

1. Light rail (subway, streetcar, etc.)
2. Charging stations for trains, buses and lorries
3. Battery buffer systems
4. Solar systems

Function of cable monitoring

The WB-CM4 is designed for insulation monitoring of power cables and return conductors in direct current systems. It enables standard insulation monitoring between the conductor and the shield, and between the shield and earth, supplemented by monitoring for breaks between the shield and the conductor. The unit is housed in a plastic casing suitable for wall or DIN-rail mounting.

Connection and measurement principle

The conductor (A1) and shield (A2) are connected to the WB-CM4 via auxiliary leads; at the end of the cable, a terminating resistor ensures a reliable measurement. The device continuously measures the voltage between the conductor and the shield, as well as between the shield and earth, and analyses these readings. Insulation is assessed by applying voltages and specific frequencies; the evaluation algorithms used – which have been tried and tested for many years and are continuously refined – ensure that different types of cable faults are detected at an early stage.

To achieve defined measurement conditions, resistors are connected in parallel across the insulation sections; their rating limits the nominal shield voltage to approximately 40 V and the measurement current through the shield to approximately 1 mA.

Error messages

A break in the screen will trigger a ‘ground fault’ (screen–earth) or ‘internal short’ (conductor–screen) signal. A loss of track voltage is also signalled via a dedicated potential-free contact. All signals are available as potential-free relay contacts and can be integrated into a higher-level control or signalling system.

Extensions and additional functions

The WB-CM4 can be expanded to include the WB-CM41 measurement channel; the WB-CM4 continues to handle data analysis. A 5-segment display can be used to indicate the setpoint and actual status. Optionally, both systems can also measure temperature and relative humidity inside the control cabinet; remote sensors also enable the measurement of cable temperature and ambient relative humidity, e.g. in a cable duct. Measurement data can be transmitted via standard protocols; programming is also possible via an actual value analysis.

Key technical specifications

• Measurement of conductor and shield
• Measuring the shield and earth
• Monitoring the screen for interruptions
• Monitoring the conductor for breaks
• Input voltage up to 1,500 V DC, continuous load
• Measurement data transmission via protocols
• Can be expanded to include one additional measurement channel (WB-CM41)
• Programming is possible through actual value analysis

Inputs and outputs

• Potential-free relay contacts for fault signalling (internal short circuit / earth fault / loss of track voltage)
• Optional external display unit (bar graph)
• Enclosure for wall or top-hat rail mounting