TPWS Train Protection & Warning System Basic information including configuration, parts, how it works, specs and testing. This document is for information ONLY. It is NOT for testing, design, commissioning, faulting, maintenance or installation purposes. Always consult the railway standards, SMTH and SMS for installation, maintenance and testing.

F. M. Spowart Version 1.0

February 2017

TPWS Train Protection & Warning System – Page One of Eight

Contents

1. Overview 2. How it works 3. Parts 4. Types of Modules 5. Failure (Indication) 6. Specifications 7. Testing & maintenance

1. Overview The TPWS system consists of aerials (also known as loops, sensors, grids or “toast racks”) in between both rails. For the purpose of this document, the aerials are referred to as ‘loops’ from this point onwards. They are split into the following configurations; TSS: ‘Train Stop System’. These are back to back loops positioned at the signal it protects with the centre line (where both loops meet) normally within 0.6m of the centre of the signal post. (See picture below of a TSS configuration).

OSS: ‘Overspeed System’: These are the same sized loops as the TSS’s; however, these are positioned on the approach to stop signals or permanent speed restrictions. The distance is set by the linespeed, so it is imperative that if they are removed for engineering work, their location is securely marked beforehand and replaced in the same position within 0.5m. The picture below shows the OSS set-up. Due to the short distance between the OSS’s seen here, the linespeed here will be relatively low.

Extreme care should be taken when mounting loops near other on-track equipment that could interfere with the loop’s frequency output, this includes, but is not exclusive to; AWS’s (including the ramps), TI21 and Aster TC equipment, 25kV red bonds. Steel sleepers must have insulations fitted under the rail. TPWS fitment is strictly prohibited with some types of track circuit systems. See document NR/SP/SIG/10138 page 45 & 46 for more details.

TPWS Train Protection & Warning System – Page Two of Eight

The loops are configured into an arming loop, which is the first loop in the direction of travel and trigger loop which is the next loop. This is the same regardless of type of use. The diagram below shows a standard layout of the TSS and OSS with the possible distances. Note that the distance for TSS to OSS is taken between the centre line of the TSS arming loop to the leading edge of the OSS trigger loop. Some installations have only a TSS, and don’t always have an associated OSS. The minimum set speed for OSS is 15mph. Signals with an attainable speed of less than 20mph, is unlikely to be fitted with an OSS. TPWS protects trains up to 75mph. TPWS+ protects trains up to 100mph. Even though some lines have a linespeed at over 100mph, a train would be expected to be slowing down considerably when approaching a red signal, so normal TPWS would normally be sufficient enough even on higher speed lines. TPWS+ consists of an extra pair of OSS loops on the approach, these are known as OSS+ loops; see the bottom diagram showing the layout. The actual positioning of TPWS loops at initial installation is quite complex and certain criteria has to be met. This is not covered in this document. Please see document NR/SP/SIG/10138 for positioning guidelines.

TPWS normal layout:

TPWS+ (with extra OSS loops):

TSS Arming Loop

TSS Trigger Loop

OSS Arming Loop

OSS Trigger Loop

15 to 350m

Nom. (MAX

450m)

6 to

36m

Direction

of travel

OSS+ Arming Loop

OSS+ Trigger Loop

Up to 900m 6 to

36m

TSS Trigger Loop

TSS Arming Loop

OSS Trigger Loop

OSS Arming Loop

=> 3.5m from centre of TSS loops to

replacement IBJ. This can be less if

other equipment on the track

restricts positioning. See section 11

of NR/SP/SIG/10138 for more

information.

TPWS Train Protection & Warning System – Page Three of Eight

Where inner signal (AB123 in the example below) protecting a junction has a short overlap and cannot guarantee that a train will stop at it at danger, the TPWS will be positioned at the signal in rear. Outer signal AB125 will be held at red where no forward route is set. This is known as TPWS ‘OS’ (outer signal) and is termed ‘conditional double red’. The protecting signal (AB125) may also have OSS and OSS+ loops (not shown here). In some situations, signal AB123 will also have a TSS fitted. See NR/SP/SIG/10138 page 16 for more information.

On bi-directional lines, the loops are configured differently, but work in the same way (arming first

and trigger second for its associated signal for the direction of travel). It is imperative that these are

replaced in this specific order, or a train could be brought to an abrupt emergency stop if the cables

are replaced the wrong way around on the TSS at signal BA987.

In the example above, the normal direction of travel is left to right, so when signal BA123 is cleared,

the loops at it will be suppressed. The loops for BA987 signal will remain active, this is because they

are at a different frequency and will be ignored by the train.

If a train was now travelling in the opposite direction from right to left, signal BA987 will be cleared

and the loops at it will be suppressed, the loops at BA123 signal will remain active as these are,

again, at a different frequency.

The frequency is set by different coloured modules in the controlling loc and all the frequencies are

shown in the table below. The colour in the boxes signifies what modules are fitted in the controlling

location box. See page 7 for more details.

Direction Loop Arming Frequency Trigger Frequency

Normal Direction (ND) OSS 64.25 kHz 65.25 kHz

Normal Direction (ND) TSS 66.25 kHz 65.25 kHz

Opposite Direction (OD) OSS 64.75 kHz 65.75 kHz

Opposite Direction (OD) TSS 66.75 kHz 65.75 kHz

Always consult diagrams for your own areas local requirement and operation.

Signal BA123

Signal BA987

TSS (ND - Normal Direction) Trigger Loop at 65.25 kHz

TSS (ND) Arming Loop at 66.25 kHz

Trains run either way

AB123 AB125

TSS Trigger Loop

TSS Arming Loop

TSS (OD) Trigger Loop at 65.75 kHz

TSS (OD - Opposite Direction) Arming Loop at 66.75 kHz

Arrows will be shown on the diagrams

showing direction the TSS/OSS relates to.

TPWS Train Protection & Warning System – Page Four of Eight

Note that the frequencies are identical for OSS & TSS trigger for normal and opposite direction, this

is so the trains brakes will be applied if it detects both frequencies together after detecting an

arming frequency. So a train will always be trying to detect an arming frequency regardless of which

loop transmits it, providing the speed of the train is excessive or a SPAD has occurred.

The picture & next diagram shows the TPWS in use at a buffer stop at a station bay platform or

dead-end siding. Mini-loops (for OSS only) are used for this purpose, this was due to an operational

error when full-sized loops were first used, see later for an explanation in the ‘how it works’ section.

The OSS loops are positioned to give an activation of the trains brakes if it goes over 10mph.

The next diagram shows the TPWS used for permanent speed restrictions. OSS loops used for buffer

stops or permanent speed restrictions are always permanently energised and active, so a permanent

power supply is needed. However, when in remote locations a local power source is provided by

primary batteries. These are known as self-powered OSS (SPOSS) and the system requires a treadle

to turn on the power when required to preserve the dry-cell battery supply.

OSS Trigger Mini-Loop

OSS Arming Mini-Loop

Bay Platform

Normally 55m Normally

5.5m

65

Treadle OSS Trigger Loop OSS Arming Loop

It should be noted that the SPOSS is not permitted for use

with buffer stop mini-loops, as it has a speed range of 15 to

110mph.

TPWS Train Protection & Warning System – Page Five of Eight

Additional controls for complex layouts: Some TPWS’s are suppressed using the lie of points ahead. When this is used, it is known as “a complex approach”. See document NR/SP/SIG/10138 page 23 for more information. When the insulated block joints are close to a signal (less than the required 3.5m minimum distance), there is a chance that a brake activation may occur due to the signal going to red with the train-borne equipment still passing over the loop, this is known as ‘self-reversion’. For layouts like this, another relay, the V(SUPP)R is used in the controls to suppress the loop until it has fully passed over it or it may be permitted to move the TSS, but this must be approved beforehand and documented.

2. How it works When a train’s receiver passes over an arming loop a timer on the train begins to count down. If the trigger loop is passed before this timer has reset, the TPWS system will activate the brakes immediately by emergency brake application. TPWS is only active and in protecting status when its corresponding signal is at red (signal HR is de-energised), or for mechanical signals; the lever is in the normal (signal at danger) position. For the OSS the timer on different trains has two settings, one for a passenger train which is set at 974ms, and a freight train which is set at 1218ms, both +/- 2ms. This is due to the weight characteristics and braking force differences between the two. Because the TSS loops magnetic fields overlap due to their closeness, a brake application is immediate if a SPAD occurs. Earlier buffer stop TPWS used full sized loops like the ones for mainline running, and this caused a significant operational error where many trains had brake applications with no reason for one. This was due to the low speed of trains approaching the buffer stops in which the train was still over the loops whilst the trains timer had completed counting down and thus applying the brakes. To overcome this, mini-loops were later installed to give a reduced detection area.

3. Parts Due to the various sleeper types such as wood, steel or concrete and the differing track fastenings there are various types of brackets needed. Also because the TSS has two loops close together, they use different fixing kits to the OSS loops and the OSS mini-loops have their own unique brackets. A few examples are shown below:

Bracket on concrete with

Pandrol fixing (mini-loop

shown)

Bracket on concrete with

Fastclip fixing

Bracket on wood with coach

screw fixing

TPWS Train Protection & Warning System – Page Six of Eight

Loops & Brackets

Type Part Number Cat Number

Full sized type 3 604369-02 62/015031

Mini-loop 604369-12 62/015067

Mounting Bracket 804524-00 62/015025

Cable (length determined on order) & TPWS Specific Jointing Kit

Type Size Cat Number

0.75mm2 A4 6/120050

2.5mm2 A4 6/120051

2C with Earth Drain Wire 2.5mm2

C3 6/160086

Joint kit for TPWS 2c 2.5mm (for 6/160086) 54/037093

Loop Fixing Kits For TSS

Rail Fixing Type* Part Number Cat Number

Orange Pandrol 608035-21 62/015032

Black SHC 608035-23 62/015040

Brown Timber 608035-24 62/015044

Brown other concrete 608035-25 62/015048

Green Fastclip 608035-26 62/015147

Blue Vassloh 608035-27 62/015122

Red Fastclip 608035-29 62/015126 *Note: the colour stated does not represent the actual track fixing clip colour; this is just a colour coding to signify the fixing kit.

Loop Fixing Kits For OSS

Rail Fixing Type* Part Number Cat Number

Orange Pandrol 608036-21 62/015033

Black SHC 608036-23 62/015041

Brown Timber 608036-24 62/015045

Brown other concrete 608036-25 62/015049

Green Fastclip 608036-26 62/015148

Blue Vassloh 608036-27 62/015123

Red Fastclip 608036-29 62/015127

Rail Clips (some kits do not come with the track fixing clips)

Pandrol (PR427A)

57/048245

Fastclip (FC1504)

57/048055

E clip (e2001)

57/048239

Meter and test equipment

TPWS Capable Meter (with kHz scale) 94/013008

Test Aerial 62/015609

Test Jig for Maintenance/Faulting 62/015071

Plug coupler removal/reinstall tool 62/015131

TPWS Dis Boxes

Type Cat Number

3 way 86/010761

6 way 86/010762

TPWS Train Protection & Warning System – Page Seven of Eight

4. Types of Modules

Colour Used for Cat Number

RED Power supply and failure indication 110v

AC 62/015118

WHITE Power supply and failure indication 24v

DC (used for modular signalling installations only).

62/015134

YELLOW OSS Normal Direction 62/015117

BLUE OSS Opposite Direction 62/015120

GREEN TSS Normal Direction 62/015119

BROWN TSS Opposite Direction 62/015121

For a comprehensive list of parts required, please put this link into your browser:

https://www.thalesgroup.com/en/united-kingdom/what-we-do-uk-transportation-train-

protection-warning-system-tpws/products-equipment

5. Failure indication units (FIU) Depending on what type of controlling system there is will decide how the failure of the TPWS is indicated.

In a power signalbox (PSB), the TPWS failure is indicated by its associated signals red aspect going black (but not on the ground) which will also activate the first filament alarm. The failure will also hold the previous signal at red. Some newer PSB’s will have unique indications. An additional relay called a trainstop proving relay or VCR, has its contacts cut into the signals EKR circuit to cause the blackout. As soon as the affected signal clears to a proceed, the failure of the TPWS will be temporarily cleared and will be ignored until the signal is back at red where the failure will indicate again.

In a mechanical signalbox, a separate FIU master and slave is provided. One master and a

slave for each signal fitted. Failure will be indicated by a blue flashing light and an alarm. Acknowledging the alarm will cease it sounding and the light will turn into steady blue. Below is an example of a master unit (the bottom module) and three slave units for three different signals. The signaller is required to test the modules at the start of each shift or every 12 hours and record the result in their TRB.

For Westcad (or similar) systems, the associated signal number will have a blue box highlighted over it when failed, plus loss of its red indication. The failure will also hold the previous signal at red.

For TPWS’s at buffer stops, the circuit is cut into the platforms starter EKR circuit and black

out the aspect.

TPWS Train Protection & Warning System – Page Eight of Eight

6. Specifications

Warning: always consult the SMTH and SMS’s for the latest specifications as these stated below may be outdated.

Loop signal strength when energised 29mV to 53mV

Loop NOT energised 2mV MAX

Loop Frequency MAX deviation +/- 0.010kHz

Tolerance between OSS trigger and arming loops to prevent false activation

+/- 0.5m

12v supply on FIU Master & Slave Unit 9 to 15.6v

SPOSS Primary Dry-cell Batteries 11.5v min for 30 seconds

AC Input Voltage 95v MIN to 121v MAX

Securing Bolt on Loop Brackets Tightened to 8Nm MAX

Cable lengths (plug coupled) 15 or 35m

MAX cable length from loc to TSS/OSS or OSS+ Dis box

500m

MAX cable length loop feeder cable for self powered OSS (SPOSS)

100m

TSS centre pivot (where loops joined) to signal distance

+/- 0.1m

Centre line of loop to both rails +/- 10mm

Loop Height MIN 60mm, MAX 100mm For a useful TPWS test card layout and what readings to expect; go to www.nremployeesite.yolasite.com and click on ‘Information Record Cards’.

7. Testing & maintenance Testing of the TPWS can become complex depending on the nature of the failure and may not always be the actual on track or trackside TPWS equipment, but could be the interlocking (SSI modules etc) or a fault with the train that reported a brake activation, especially if the failure affected just one train. However, all failures must be investigated. There have also been incidences where a train has had a brake activation and the driver has still reported it even though they have also admitted they were going over the linespeed. In this case the TPWS has done its intended job and further action may not be required. Your Line Manager will advise on the course of action, this is usually after the data has been downloaded from the train to determine the actual train speed. Because there are many flowcharts included in the SMTH failure and incident test guides, there is no need to repeat them on this document. Please go to SMTH section Part05/FF12 & 13 for the failure flowchart and guidelines. Where a wrong-side failure is confirmed or suspected, please refer to SMTH Part05/T019 for guidelines. Equally, maintenance is covered by the SMS’s and is a controlled document, so please refer to SMS TP11 and test 025 for the latest specification and testing.

By F. M. Spowart Ver1.0 March 2017