TRACK TECHNOLOGY
lised a moulded plug and socket arrange- ment, which connected each heater to the multicore cable to feed off track. This ar- rangement became the weak link in the whole installation and invariably failed in service, requiring the technician to attend site and gain access within the ‘4 foot’; not easily achieved on an operational railway.
To resolve this problem, Graybar introduced two types of off-track junction box for termi- nating the heater power supply cables.
These junction boxes are positioned safely off the track in the cess, can be post-, base- or wall-mounted and are available in a small and large box size with terminals lo- cated within. Network Rail-approved dura- ble heatshrink glands complete the assem- bly and this method ensures easy access for the maintainer while providing a securely sealed unit.
Control Cubicle
An integral part of any point heating sys- tem is the control cubicle that stands at the side of the track and distributes the power supply to each set of heaters on the point ends.
This cubicle, known as a ‘PHCC’ contains a weatherstation and the circuit protective devices and is used with all types of electric strip heating.
However, a further major benefit when using our self-regulating heaters is that the transformers do not have to be placed along the track, contained within large heavy steel tanks, but can be placed within the PHCC itself as a physically smaller unit resulting in a number of advantages.
Firstly the maintainer can gain easy access to the 110 volt power supplies without hav- ing to walk trackside, very often at night, at greater potential risk to safety than be- ing in one location at the cubicle. A further advantage is in the monitoring of the cur- rent draw of each heater, which provides instant evidence of a cut cable for instance. The internal transformers, naturally air- cooled and placed conveniently on shelves, are typically rated at 5kva and are less than half the cost of jelly-filled trackside trans- formers.
In addition, there are no armoured cables to run alongside the track in dedicated troughing routes and no undertrack cross- ings (UTX) are required because all the ca- bles can be surface laid.
Finally, there are no bonding issues to consider, because there is nothing metallic
between the PHCC and the heaters them- selves.
The Graybar integral type control cubicle, or PHCC, is designed specifically for self- regulating point heating, and is simple in its functionality; for example, there are no rail temperature probes required because the heater itself ‘senses’ the rail tempera- ture along its length and draws the correct power accordingly.
The cubicle-mounted weatherstation pro- vides the necessary control from the sen- sors and is mounted on the rail sidewall of the PHCC. It detects low temperature and/ or precipitation of the local area weather conditions. It is essential that any weath- erstation will give early prediction of the changing weather conditions in order to activate the point heaters in good time, rather than wait for the rail temperature to fall below zero degrees with the potential for a resultant points operation failure.
Remote condition monitoring (RCM) can also be added within the points heating control cubicle and can provide various levels of monitoring, from a simple moni- toring of the power supply to the heaters to a sophisticated, fully-integrated system where the PHCC can be remotely interro- gated and controlled from a central control room.
As the heaters are individually fed from the control cubicle, this provides a unique abil- ity to measure each individual heater pow- er draw and alarm the system as required.
Cable management Until recently, point heating systems uti-
Being of GRP construction with insulated glands and using non-armoured cables, the junction boxes do not require any electrical bonding to the PHCC.
The popular post-mounted junction box part numbers are GBK 1774P, NR PADS 0055/020813 (small size) and the GBK 1493P, NR PADS 0055/021034 (large size) and these are now becoming the standard method of terminating all points heater tail cables.
Other applications for the self-regu- lating element
Rail head heating
Among the many benefits of the self-reg- ulating heater elements is the ability to have long lengths of a single element. This is possible because the element is flexible, with a parallel circuit. The construction of the heater allows for a circuit length of up to 25 metres for the 110 volt product. This avoids having many short lengths of heater and associated management of the cables.
In certain locations, steep gradients bring adhesion problems for modern lightweight rolling stock and therefore there is a need to keep the head of the rail as dry as pos- sible. Our self-regulating heater element is an ideal solution to this problem as it can easily be mounted against the web of the running rail, under the rail head, where it can inject enough heat to keep the rail head dry under adverse conditions such as rain or heavy dew. The control method is rather different to points heating as the heating is initiated in this case by a dew point detec- tor mounted adjacent to the rail at the same height as the track being heated.
rail technology magazine Apr/May 11 | 163
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