1. LABORATORY INVESTIGATION OF THE SWEDISH TRAIN DETECTION SYSTEM Åke Wisten Luleå University of Technology

2. Lab tests of the train detector system
The Swedish train detection system has been tested in a laboratory.
1. Testing the delay times for switching the signals : red to green, green to red
2. Testing the influence of a lightning strike in the neighbourhood of the rails

3. 1. Testing delay times
Testing delay times for switching the relays, corresponding to the entrance of a train, and the departure of a train, from an I-rail-section.

4. Feeding voltage of the I-rail
Voltage feeding of the I-rail: The I-rail is always connected to a 6 V DC battery, with very low internal impedance, and a very big inductance (0.3 Henry) in series. The low voltage side of the inductor is permanently connected to the I-rail. The negative pole of the battery is connected to ground (ground = the S-rail).
During the lab-test the breaking of the I-rail feeding circuit was done between the battery + 6VDC pole and the inductor. The voltage was measured between the battery and the inductor.

5. The train detector circuit
The I-rail voltage is controlling a relay. The I-rail is connected to the primary port of the relay. When the I-rail voltage is 6 V, the secondary contacts are closed. When the I-rail voltage is 0 V, the secondary ports are open.
In the detector circuit there is an adjustable resistor, and a very big inductor in series with the primary port of the relay. The adjustable resistor is needed for adjusting the switching voltage level. The inductor is needed to protect the relay from fast changes in currents. For safety reasons there are two relays on each I-rail section.

6. Breaking the 6 V feeding voltage
Voltage measured at the I-rail feeding 6VDC circuit. The primary 6 V DC-circuit is opened at time 0.1 seconds. A spark is closing the circuit again for a short moment (shows as an 8 V peak). Then the circuit is definitely broken – and the voltage goes to zero.

7. A train is entering the section
Voltage at an output port of the relay. Delay time for switching from ”no train on the section ” to ”train on the section”: – 0.1 s = 0.23 seconds

8. The train is leaving the section
Voltage at an output port of the relay. Delay time for switching from ”train on the section” to ”no train on the section”: 1.45 – 0.1 s = 1.35 seconds

9. 2. Testing lightning strikes
Testing implications of a high voltage discharge, similar to an indirect hit by lightning in the neighbourhood of the I-rail
A 30 kV, 6.2 nF capacitor was discharged against the I-rail. The purpose was to investigate if the train detection relays were influenced by the “lightning strike”.

11. Testing lightning strikes
When the 30 kV capacitor was discharged at the I-rail a 3 cm spark was generated. The time-duration of the spark was measured by means of an optical fiber between the spark and a photodiode.

12. Duration of the lightning spark
Measuring duration time of a spark. The signal from the photo diode, showing the duration of the spark. The duration of the spark was about: 4 us.

13. Duration of spark in detail
Measuring duration time of a spark. The duration of the spark was measured by means of a photodiode. The duration of the spark was approximately 0.4*10 us = 4 us. The rise time was approx. 0.2 us.

14. Sparc interference on left relay output
Voltage at a secondary port of the left relay, when the spark was hitting the I-rail. The maximum interference-voltage was 15 V.

15. Sparc interference on right relay output
Voltage at a secondary port of the right relay when the spark was hitting the I-rail. The maximum interference-voltage was 18 V

16. Sparc interference on relay input
Voltage at the input port of the left relay when the 30 kV discharge was applied at the I–rail. The maximum voltage in this case was 12.5 kV. The width of the pulse was about 0.1 ms.

17. Test conclusions Conclusions.
The delay time for switching green light to red light was 0.21 seconds, and from red to green 1.35 seconds
When a very strong lightning-discharge was applied on the I-rail no disturbance on the functioning of the train detection relays was noticed.
The experimental lab setup can be used for checking computer models of the train detection system.