Radar BetuweRoute

Market Focus: Industrial Safetywww.engineersonline.nl12th December 2006

Next Generation Radar Sensors for Tunnel Project

Author: Robin ZanderDutch-English translation by Google Translate and Brendan Funnell

As everything goes according to schedule, the Betuweroute will be operational on January 1 next year.

The delivery of a 160 km long route from the port of Rotterdam to the German border represents one of the most exciting general infrastructure projects around. It is expected that one billion euros will be invested over the course of the project.

Safety is crucial at many levels in this project. One innovation is the application of a new generation of radar sensors.

Figure 1. The Sophia Tunnel is 8km long, including a 4km bored section - the longest tunnel in the Betuweroute.

Both socially and technically, the Betuweroute is a controversial project.

Together with HSL (High Speed Line), the Betuweroute is one of the first two lines in the Netherlands with a 25kV AC overhead power supply, instead of the standard 1500V DC used elsewhere on the Dutch Railway Network. This increased power allows longer and heavier trains to be used.

The Betuweroute is also one of the first lines in Europe to use the European Rail Traffic Management System (ERTMS). In conjunction with the European Train Control System (ETCS) on the train itself, ERTMS monitors and controls the traffic on the line as a whole.

Communication between ERTMS, ETCS, the traffic and the driver takes places through a dedicated railway GSM network – GSM-R (Railway).

With ERTMS and ETCS in place, the positions and speeds of trains are known at all times, meaning that maximum speeds and required braking distances are continuously calculated, and trains can safely run closer together.

Furthermore, all crossings on the Betuweroute make use of flyovers, eliminating the risk of collisions with other vehicles or people.

Sophiatunnel

In the route from Rotterdam - three quarters of which runs parallel to the A15 - there are five tunnels: the Sophia, the Botlek, the Giessen, the Pannerdensch and the Zevenaar. Part of the line that travels through the city of Barendrecht is also covered.

The Boltek tunnel was the first to be bored in the Netherlands. The Sophia tunnel pictured here (figure 1) runs from Zwijndrecht to Papendrecht and is the longest in the Betuweroute with a total length of 8km.

The Sophia tunnel consists of a central bored section of two tunnel tubes, 4km in length, running between the towns of Henrik Ido Ambacht and Oud Alblas. On one side of this bored section is an open cut tunnel, and on the other a closed cut tunnel. A tunnel underneath the Pannerdensch canal is also a bored tunnel.

Weir

The Sophia tunnel runs underneath the reclaimed island reserve of Sophiapolder (the tunnel’s namesake) and also the two waterways which encircle it - the River Noord and its parallel stream the Reitbaan. The location of this tunnel section alone demands particular care and consideration.

In the unlikely event of leaks on both sides of the island, hydraulic slides can deploy in order to seal the tunnel and prevent the island (which is below water level) from flooding. (Figure 2,3.)

Disaster Scenario

Another potential disaster that will hopefully never occur is a burning train within the tunnel. If a train were to catch fire inside the tunnel, every effort would be made to bring the train to an exit. If that is not possible and the burning train stops, then it becomes very important to quickly extinguish the fire. The entire tunnel is equipped with sprinklers, but only in the event of a stationary fire are they activated, as a moving fire would require too great a quantity of extinguishing agent to be stored.

Because only freight trains operate on the Betuweroute, the primary aim of the fire extinguishing system is to prevent damage to the tunnel itself – damage that is most likely if a fire is concentrated in one position.

To assist train operators in escaping a fire, cross connections between the two tunnels, and shafts to the surface are also provided.

Figure 3. One of the hydraulic sliding doors. If the water were to leak in from the Noord or the Reitbaan, the doors would close and prevent the polder from flooding.

Figure 2. (left)

The Sophia tunnel (in red) crosses the River Noord, the island of Sophiapolder, and the Reitbaan.

Detection

Before any fire can be managed or extinguished, it must first be detected. Located on the tunnel ceiling, either side of the overhead power wires, are two multimode fiber optic cables in a stainless steel housing. This system, which is divided into measurement areas of 15 meters, determines if there is a fire anywhere in the tunnel by sensing temperatures in excess of 58 degrees centigrade. However, this system is not able to reliably distinguish between a slow moving train and one which has stopped, nor is it able to pinpoint the exact location of the complete train within the tunnel. Tunnel builder GTI Infra BV (now Fabricom) and technology partner Rockwell Automation Ltd have joined forces to find a reliable way of obtaining the data required. Nevertheless, there have been some worries about costs.

Too Slow

Initially, ultrasonic sensors were trialed. For a variety of reasons they proved to be a less than ideal solution. The primary reason is that ultrasonic sensors can be slow. A stated requirement for the detection system was that three distinct velocity ranges can be reliably distinguished.

Arrest (slower than 1 m/s)Crawl ( 1-10 m/s)Moving (faster than 10 m/s)

Due to the relative slowness of sound waves compared with electromagnetic radiation, it was found that ultrasonic sensors were not able to reliably detect trains in the upper range of speeds experienced in the tunnel (up to ~120km/h).

Reflector Undesirable

Furthermore, the use of an ultrasonic sensor demands that the sensor be aimed at a reflective plate. Because the primary aim is protecting the tunnel, it is undesirable to attach more objects to the tunnel wall than is strictly necessary. In addition, the ultrasonic signal must strike the reflector at an exactly perpendicular angle. Not only is it time consuming to install these sensors in such precise alignment, it is a challenge to maintain the alignment with freight trains rumbling through the tunnel.

In trials, it also became apparent that the pressure wave generated by the train in the tunnel could cause the signal to be ‘pushed.’ Thus it is possible that a train could be detected in the wrong location, or with an inaccurate length.

Magnetic sensors can also come in for some criticism, the magnetic field of the overhead wiring being one proven source of inaccuracies.

FMCW Radar Sensor

Ultimately, the search centered on a new generation of radar sensors. These sensors from Banner Engineering were in the prototype stage last April, but are now fully developed. In The Netherlands, these sensors are distributed by Turck BV, working closely with ORLD Banner Engineering.

The R-Gage is a radar vehicle detection system that works according to the principle of Frequency Modulated Continuous Wave (FMCW – see Figure 4). This means that continuous signals of different frequencies are broadcast - in this case using the 24-24.25GHz range. The relationship between the frequency of the emitted and received signals determines the distance between the sensor and the detected object. Important additional benefits of this radar technique are a relative immunity to dust, soot and pollution, the lack of requirement for a companion reflector, and the simple ‘teaching’ procedure required.

Stationary Objects

Unlike Doppler radar sensors, FMCW radar sensors are capable of detecting stationary objects. A Doppler radar sensor works with a single frequency signal. Incoming and outgoing objects create reflections of slightly higher or lower frequencies, and my measuring these discrepancies a velocity and direction may be measured. However, with a stationary object, the frequency does not change, and it is therefore impossible for a Doppler mode radar sensor to distinguish between a stationary object and no object at all.

Another common technique is to use pulsed radar. Pulsed radars measure the time between when a radar pulse is sent and when it is received. This technique is mainly used for level measurements. However, even with fast pulses it is possible that a pulse could pass between two moving wagons, resulting in an unreliable signal. It must also be taken into account that a typical pulse radar does not measure continuously, but about once per second.

Figure 4. Important additional benefits of the radar sensor are an insensitivity to dust and soot, the lack of requirement for a reflector card, and the quick, easy ‘teaching’ procedure.

SCADA – Supervisory Control and Data Acquisition

With the R-Gage, GTI Infra management obtained a state of the art FMCW radar sensor that satisfies their specific requirements. In the tunnel, radars are installed at a rate of one every 30 meters. An exception to this is beneath the two waterproof doors, where double sensors are used to ensure that a train is not present before the doors are closed. In each tunnel, there are 202x R-Gage sensors in total.

The signals from the sensors are transmitted via remote I/O over fiber to the PLC (Programmable Logic Controller). On the parent RSView SE SCADA system – like any applied PLC system from GTI Infra partner Rockwell – the various inputs are combined and monitored. In conjunction with a GTI Infra developed algorithm, the speed, length and current position of each train is derived. Notably, the system is capable of detecting and managing up to simultaneous two fire events per tunnel. This means that even in the event that a burning train becomes separated, the system is ready to respond.

Figure 5. A passing train, seen here in the Botlek tunnel. In the RSView SE SCADA system from Rockwell, the speed, direction and length of trains are derived from the signals from the sensors.

Green lights show where a train is detected.

Four Million Liters

When excessive temperature is observed, and the radar sensors confirm that the burning train is stationary, the system will engage and fight the fire. The automatic sprinkler system is able to draw from up to four million liters of water, plus an appropriate amount of foaming agent. Sprinklers activate along a 120m stretch, directly above the fire, pouring down water and foam.

As a secondary measure, large fans can also be activated if a fire is seen to be spreading. Extra sprinklers will activate upwind of the fire, creating a dense extinguishing mist that is then blown onto it. This system not only assists with fighting the fire, but also helps to cool the tunnel wall and limit or prevent any damage to the tunnel itself.

Availability

The R-Gage sensors, in combination with the operating system designed by GTI Infra, make an important contribution to the safety of the tunnel. With the implementation of these sensors in the Betuweroute, GTI Infra are clearly setting a new standard.