A pantograph is an apparatus mounted on the roof of an electric train to collect power through overhead tension wires, known as the catenary. Over the years, reliable pantograph monitoring has become an important discussion point, as this is the dominant form of current collection for modern electric trains.
For reliable operation of trains, the pantograph and catenary must maintain proper contact at all times to ensure minimal electrical energy losses, limit wear and tear, and reduce the risk of current transmission disruptions to the power unit of the train. This contact is dependant on the vertical position, horizontal position, and the tension of the catenary. Continuous monitoring of these factors is crucial for successful preventative maintenance as it allows early detection and timely repair of irregularities and avoids severe infrastructure damage. Different continuous monitoring methods have been tried and tested with various levels of success.
Traditional methods for pantograph monitoring
The first and most traditional monitoring method makes use of specially equipped overhead line measurement wagons that periodically check the position and tension of the catenary. However, due to the size of railway networks, the interval between these line inspections are lengthy, and changes are not detected in time or even remain wholly undetected.
The second solution is to instrument standard commercial pantographs to measure the contact forces between the catenary and pantograph. This instrumentation enables trains to gather measurement data during day-to-day operation which is combined with GPS data to form a continuous health monitoring system. The system can identify the location of problem areas and provide warnings of maintenance requirements. However, reliable results are hard to obtain because the pantograph operates in a high voltage environment (15-25kV) that influences signal leads from conventional sensor technology. Following this, it’s clear that there is a need for technology that can instrument the pantograph to make this monitoring system more reliable.
Pantograph monitoring using Fibre Bragg Grating (FBG)
Finally, after many years of research, it became possible with the advancement of fibre-optic measurement technology such as strain gauges using Fibre Bragg Grating (FBG). A study conducted by the Austrian Research Promotion Agency (FFG) proved the concept of FBG-based sensors in this application, as glass fibres are naturally non-conductive and can deliver reliable force and acceleration measurements in a high voltage environment. Due to this, it’s possible to measure the pantograph’s contact forces, including lateral displacement of the overhead contact wire, momentary vertical contact forces, and detection of impermissible force peaks and loss of contact.
Based on this, HBM developed compact, low-weight, FBG-based sensors that can cope with the harsh environment of railway applications. First is a force transducer that, mounted between the pantograph head and the contact strip, achieves direct force measurement. The second is a fibre-optic accelerometer that considers the effect of inertia on the contact strips.
A complete onboard pantograph monitoring system
Together, these robust and reliable FBG-based sensors form a complete onboard pantograph monitoring system that’s suitable for any electric train. HBM’s QuantumX multi-channel data acquisition is the data backbone of this system, allowing integration of FBG-sensors, analog sensors, cameras, GPS, and vehicle data.
Measurement data is communicated to data centres or the Cloud through open connectivity via wi-fi, ethernet, or mobile data networks, enabling continuous condition monitoring and automated maintenance notifications via an event-triggered SMS or e-mail.
HBK’s pantograph measurement system meets the following criteria:
- measure the sideways movement of the contact wire
- detect undesired peaks in contact force between the catenary and pantograph
- detects contact force relief of the pantograph
- localise obtained results to a position (+/- 1 m) on railway track record data
- monitor thresholds to provide immediate notice in critical conditions
- fully autonomous, 24/7 operation
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