01.01.07
Fluke Thermal Imagers help keep the trains on time
So many overheating connections and fuses may currently go undetected that they could lead to very expensive train stoppages. It is therefore hardly surprising that the arrival of fully radiometric thermal imaging cameras offering easily identifiable diagnostic images, like the Fluke Ti20, has led to their widespread use in trackside preventative maintenance.
Steve Kennedy, signalling support engineer at Hither Green, has been using one of the new line of portable Fluke thermal imagers for the past 12 months. He is very enthusiastic about the benefits that the product has brought to his team.
“I had been keen to buy a professional thermal imager for a number of years, but the prices had always been so prohibitive. When our specialist distributor showed us the Fluke thermal imager and allowed us to trial it for a couple of weeks, I knew it was the solution for us. In the past year it has identified many hotspots for us before they have caused downtime on the network. My team has the responsibility to investigate frequently recurring faults which the regular maintenance team are finding particularly difficult to solve. We now use the Fluke thermal imager every day and are continually finding new preventative maintenance uses for it”.
Steve says that the instrument has some particularly successful applications. “High resistance fuses in relay bases in the Hither Green relay room kept failing due to overloading. Imbalanced traction returns can cause unnecessary red signals. Busbars in location cases may overheat and cause problems with signalling, points control and the train protection and warning system. And points heating elements may fail without warning. Most of these events trigger changes in localised temperatures in advance, and the thermal imager can register these problems from a safe distance before they cause major downtimes and hold ups in the train network.”
Overloaded fuses
In a typical relay room there will be rows and rows of relays with high resistance fuses in their bases. In time, the resistance wire and its connections to the end sleeves will gradually deteriorate until they run hotter and hotter and eventually blacken and burn out. But when there are rows and rows of them which could overheat and fail, how do you predict which will go next? An overheated fuse shows up clearly on the Fluke thermal imager screen and can easily be identified physically from the rest.
Imbalanced traction returns
The track circuit requires the running rails to be divided electrically into sections by means of insulated block joints, so that the current position of a train can be electrically detected within a particular section of track. In order to complete the electrical traction circuit from the sub-station via the live rail, through the train’s motor and back along both running rails to the sub-station, impedance bonds are located at the junction of each section of track. The impedance bonds are linked to both running rails either side of the insulated block joints by 4 large side leads which may carry up to 500A DC. Inevitably, over time the connections suffer from problems such as corrosion and vibration, causing an increase in resistance, and the cable itself may deteriorate. This leads to an electrical resistance imbalance between the parallel traction returns.
The track circuit uses an AC signal in the circuit between two successive impedance bonds and along the parallel running rails. Even a small resistance imbalance in these traction returns may lead to a voltage drop in this section which is sufficient to revert a signal to red incorrectly creating a signal passed at danger (SPAD).
But this can be avoided by regular inspections with the Fluke thermal imaging camera. Poor connections and cables will show up clearly as high temperature zones on the screen, enabling maintenance work to be carried out well in time before SPADs are invoked.
Points heaters
With around 66,000 sets of points on the complete UK rail infrastructure, each with their own heating elements to prevent freezing, preventative maintenance becomes a big chore in the run up to winter. A quick check that each heater is still working can now be done at a distance with the Fluke thermal imager. No hand contact with the rails, no walking on slippery sleepers. It can all be done from the side of the track, even from overhead bridges.
Other preventative maintenance uses of the Fluke thermal imager
• points are typically powered by rechargeable batteries. Corrosion to the battery terminal connections will eventually lead to high resistance and failure to provide enough energy to operate the points. But high resistance means high temperatures and again thermal imaging can easily pick this up in advance
• busbars in trackside location cases which control systems like signalling, points and the TPWS, will sometimes overheat prior to failure of a component such as a fuse. An overheated busbar can easily be spotted by opening the door and taking an image of the complete case
• the continuing operation of heaters in location cases to prevent the build up of moisture can quickly be checked with a thermal imager, and over-temperature location cases in high temperature locations can be identified at a distance.
Reporting
All the images captured by the Fluke thermal imager can be stored for later downloading to a PC. Easy-to-use software provided with the camera offers detailed temperature analysis as each calibrated point on the screen stores a temperature reading. Previously captured images can be compared with the latest image, and images can be imported into a report if required.
Summary
Steve Kennedy concludes, “It all comes down to our key objective - keeping the trains running on time. The Fluke thermal Imager is proving to be a very valuable tool to identify the need for preventative maintenance. If we can see a problem developing before it actually creates a trackside fault, then the train operator is not affected, the passengers arrive on time and the operator of the rail infrastructure is not penalised financially. This is all made possible with a handheld tool which can be operated at a safe distance. Customised on-camera inspection routes can be set up if required.”
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