AWS system. Introduction, Layout, Installation and Testing. Copyright F. M. Spowart

Transcription

1 AWS system Introduction, Layout, Installation and Testing This document is not endorsed by Network Rail. It is NOT for installation, commissioning, testing or maintenance purposes, it is for information only. Network Rail s own documents must be followed at all times, however; this contains re-written extracts from railway standards. All pictures are copyright of the author. Copyright F. M. Spowart March 2015 Version One

2 AWS system Introduction, Layout, Installation and Testing Introduction: The AWS system was introduced in the 1950 s as a reminder device for the driver and a means of stopping a train if the driver did not acknowledge the signal not clear warning. The AWS is fail safe and only needs power to give a clear warning by means of a bell in the cab, meaning the signal head was showing a green by the signal DR* relay being energised. If the DR is de-energised i.e. the signal is at double yellow, single yellow or red it would sound a horn in the cab of the train. The driver has 4 seconds to acknowledge this warning and start to apply the brakes or they would come on automatically. Unlike the more modern TPWS system it will not stop a train if it passes a signal at red or if it is speeding, it is also unlikely to prevent a SPAD. Operation: To give an all clear bell warning, the electro magnet (also known as an Inductor) at the rear (travelling direction) is energised by either 12, 24, 60 or 110v via the signal DR energised *OR the semaphore arm is between 25 and 65 degrees. (60 and 110v green magnets only). The front magnet called the permanent magnet is always a naturally powered magnet unless it is suppressed. On single or bi-directional lines the permanent magnet may be replaced with a magnet that is powered (see last page). This is called a suppressed magnet; this is so it is turned off when a train is travelling in the opposite direction to the signal it is protecting. As the train passes over the permanent magnet (south pole magnet) it is picked up by the train, almost immediately it passes over the electro magnet (north pole). If the train only picked up the permanent signal it would sound a warning horn, however, if the electro magnet was energised, the signal from this magnet would cancel it out and give an all clear proceed at linespeed indication. In the cab along with the horn or bell signal, a dial known as a sunflower (pictured below) displays the state of the AWS. An all black dial signifies an all clear notification, whereas a black and yellow display signifies a warning to start to apply the brakes.

3 Where and how it is mounted: The normal location is usually 200 yards (180m) on the approach to the signal it is protecting. However depot magnets used to test the receivers on trains are mounted at set places according to local requirements. Also advanced warning AWS s are mounted beyond the signal. These are not copying the signals but are actually energised by a track circuit. If a train passes over them and gets a warning, it means the track circuit has failed to occupy and the train must stop. These unusual installations are used at junctions where the exit point (from a power station for instance) maybe be rarely used and suffer from rusty rail failures. The AWS comes in various fittings, and coloured either yellow for 12 or 24v DC operation or green when powered by 60 or 110v AC. The green inductors are higher powered for lines where third or fourth rail is fitted. The AWS is mounted in the four foot on either wood, concrete or steel sleepers. If mounted on wood it is secured to the sleeper by 5x 3/4 coach screws, with the height adjusted using packing discs. If mounted on concrete, mounting plates are used. These are fixed to the sleeper by Hilti rawl bolts which when fully tightened the red cap snaps off indicating they are at their correct torque. Holes for these are drilled using a 18mm masonry bit and drill powered by a 110v generator. The holes can only be drilled centrally using a marking template as reinforcings in the sleeper prevent drilling off centre. When mounting on concrete, the plates are reversible for the correct height. For sleepers that have a level top, the plates are mounted flat side down so the lugs are facing up. If the sleeper is indented which curves down after the pandrol (or other) fixings, the plates are mounted so the lugs are face down and the flat surface of the plates are upper most. The bolts used to fix the actually inductors and ramps depends on which way around the plates go. Pan head bolts for when the plates are mounted lugs down, or flat head bolts when the plates are mounted flat side down. The bolts are also various lengths as the inductors are thicker in depth than the ramps. Fitting to steel sleepers requires the sleeper drilling and using special hook bolts which are slid into the holes and then a special two pinned tool is inserted to open out the hooking mechanism so the locking nut can then be tightened whilst the hook stops the bolt pulling through. Ramps are fitted on the approach side on the AWS or both sides if on single or bi-directional lines. Special extension brackets and/or bridging brackets are also used to close the gap where ramps are fitted up to the electro magnet on these lines. The cabling to the AWS is usually with 2.5mm squared 2c cable, but always check the diagrams as some maybe connected with 10mm squared. A dis box must be provided before it is terminated into the AWS, orange pipe is no longer used, so the cable is cleated to the sleeper. The AWS magnets are to be set at +/- 12mm from the top of the rail. This is checked by a piece of string and a treadle gauge over the magnets. However, if it is above rail height, a straight piece of wood or similar can be used and then the treadle gauge used on the rail head to take the measurement. A measurement must be stated on the record card, writing level is not acceptable. ROSE requirements state that the cable entry into the inductors are properly sealed and the lid on the termination boxes are sealed using a silicon type sealant.

4 The Layout: Green electro magnet Green permanent magnet Termination box Mounting plates (shown flat side down and lugs facing up) Ramp This is a high powered AWS mounted on concrete. One ramp signifies it is on a uni-directonal line. It would look exactly the same if yellow magnets were used. Note: orange piping is no longer used to secure the cable; it must be cleated to the sleeper.

5 Permanent magnet, this may be suppressed (see last page) One of two Mark Two electro magnets Special bridging plate One of two ramps Special extension piece Mounting plates, this time shown lug side down, flat side up This yellow AWS installation is on a bi-directional line so there is a permanent magnet, two ramps, special plates to close the gaps. On this particularly installation because two signals are close to each other both electro magnets are installed together. This is the maximum amount of fittings in one installation possible. This is a suppressor inductor, which has a sump type bottom which the ballast is dug out.

6 The fittings: These are the different types and lengths of bolts used. On the left are flat head bolts, and on the right are pan head bolts. Their use depends on which way around the mounting plates will go. Flat head used when plates are flat side down so they are counter-sunk into the plate and the antiturn tab is locked into the slot to stop it turning when tightened. Pan head bolt used when the plates are lug side down. They then don t need to be flush. Again the anti-turn tab locks into the slot.

7 This is a rubber adhesive mat that fits under the plates when mounted lug down onto concrete. This is the special packing plate used to lift the height if required when mounted directly to the wooden sleepers. The coach screws for mounting the magnets directly to wooden sleepers. The Hilti rawl bolts used to fix the plates to concrete sleepers. The heads of the Hilti bolts snap off when tightened indicating they are at the correct torque. Testing: This is the marking template to centre the AWS when installing for the first time. It fits in between the pandrol clip housing. The clips will need removing beforehand.

8 Testing: The SMTH must always be used when testing a magnet after any work. Consult the current SMTH specification as it may change. The testing of a AWS is carried out using a strength and polarity meter, known as an S&P meter or Flux meter. Green coloured is for testing green extra strength inductors, and gold for testing yellow inductors as shown below. Moving strength needle Polarity window Measuring strength: The strength of the inductor is measured using the coloured sectors. The meter is placed onto the centre of the inductor and reading observed, note that if the inductor is an electro magnet the signal must be displaying a green aspect or off if a semaphore. The needle in the green sector indicates the magnet is healthy and no further action required. If in yellow sector it is failing and needs replacing as soon as possible. If the needle is in the red sector the magnet has failed or no power is getting to it. Check power is ok and if so, sign out the AWS and restrict the signal to double or single yellow by disconnecting the DR relay links. If the permanent magnet has failed its strength test, the signal in rear must be restricted to red as a permanent magnet not working will not stop a train if it has failed. However permanent magnets failing are extremely rare. Measuring polarity: The small window is for the polarity, (which also measures the poles). In that window a letter E or P will be displayed depending on the magnet tested, i.e. E for electro and P for permanent. No letter is displayed if either it is not being used, or the polarity is incorrect. If the meter is placed on a magnet and no letter is displayed when it should be, then check for power and if power is present check the 2c cable is the correct way around and the internal strapping plate is also correct (SMS Part Z for strapping arrangement). Fault codes as used by Control are used to determine a reported fault. Codes 5 and 7 are wrong side failures. All codes are listed on a RT3185 form. Fault conditions may be caused by no or low strength in the magnets, polarity incorrect, no power to electro or suppressed magnets, (blown fuse/tj, cable cut or stolen/dr contacts faulty/loose or missing links etc), or incorrect height of the AWS; so although strength is indicating good on meter, the magnets are too low for the train to receive. Maintenance: The AWS is now subject to ROSE restrictions and once it has passed ROSE criteria, the AWS is no longer maintained. Consult the SMS ROSE section for more details and current maintenance regime.

9 The basic circuitry: 110v AC 101 DR V D1 D2 101 DR V D3 D4 101 (AWS) TJ BX110 NX110 1A v DC 101 IJ (AWS) I BOTTOM TOP 2 3 The basic circuitry shows the TJ, the energising DR contacts, the diode and the inductor which should state the termination details and also the internal strapping depending on voltage used. Note that on older circuits, the DR contacts may be on the right and after the TJ. The diode is used in the circuitry to stop damaging back EMF voltages blowing the TJ when the AWS is powered down. Also note that if controlled by a semaphore, the DR contacts will be replaced by off circuit breaker contacts. On suppressed AWS circuits, the DR will be replaced by special controls such as (SUP)R contacts, or if on a single line with direction lever it may be controlled by (ACC) LR contacts, see your own diagrams to check for the specific controls. Not all permanent magnets may need to be suppressed. If two signals are close to each other on a single line the magnet will act as permanent for both signals, and either electro will cancel it out when associated signal is at green, as indicated in the diagram below. Permanent magnet not required to be suppressed (signals close together): Direction of train Electro energised (de-energised if train going the other way) Permanent acts for both signals Electro de-energised (energised if train coming other way) Permanent magnet required to be suppressed (signal on its own): Direction of train Electro de-energised as the train is going away from the signal Permanent is now a suppressed magnet so it doesn t stop a train travelling in the direction shown. It will energise when signal is cleared/or when route is cancelled.