**2. Description of the problem**

Disturbances in electric and electronic circuits are problems that appear while designing and implementing a system. Bearing in mind the presence of electrical disturbances (radiated or driven) systems are design in order to avoid or lessen the effects of these phenomena.

In the case of existing railway services there are not effective preventive measures since the electrical 50 Hz disturbance problem was not present while designing those equipments and facilities for the railway line. So preventive measures have to be developed and implemented long after the line is in service. The main measures that are carried out in order to lessen or avoid these problems are:


The presence of these high speed lines have two main ways of electrical interfering with the

• Disturbances in the existing lines due to 'direct contact' between both systems. This occurs when a train transits between both systems. This usually takes place in the gauge

• Disturbances in the existing lines due to the presence nearby of a high speed line. This electrical disturbance is related to magnetic induction and electrostatic electric fields. The Centro de Investigación en Tecnologías Ferroviarias, CITEF (Research Centre on Railway Technologies) that belongs to Universidad Politécnica de Madrid has a long dated expertise dealing with this disturbance matters that affect existing railway lines in the Spanish case. CITEF expertise is required in order to analyse and calculate the determined probable disturbed sections so preventive actions can be carried on well ahead before disturbance can affect those facilities. Once the new railway lines are totally functional and before open them to commercial services, CITEF engineer are required to perform electrical in-field measurements in the disturbance-susceptible sections in order to validate that the disturbance levels can't act against the safety of the railway line. There are singularly important measurement points that are those that confirm the border between the protected

so called 'conventional lines'. These interferences can be split into two main blocks:

railway line zone and the unprotected against these electrical disturbances zone.

This chapter is structured following a usual approach. First of all there is a description of the disturbance problem, why it is important to detect and apply measures in order to mitigate or eliminate those effects. After that there is a section where there is a description of the physical principles that intervene originating the disturbances and those physical principles that can help to solve them. This section is the most academic part of the chapter with the use of formulations and equations. The next section gives a guideline referring what to do in

The following section shows the methodology used in order to measure the effect of the disturbances in the 'conventional' facilities and equipments. Some results of these measurements are showed in the next section of the chapter, precisely called 'results'. To finalise the chapter there is one section to cope with the conclusions that summarises the chapter most important aspects and the final section that shows a list of references in this

Disturbances in electric and electronic circuits are problems that appear while designing and implementing a system. Bearing in mind the presence of electrical disturbances (radiated or driven) systems are design in order to avoid or lessen the effects of these phenomena. In the case of existing railway services there are not effective preventive measures since the electrical 50 Hz disturbance problem was not present while designing those equipments and facilities for the railway line. So preventive measures have to be developed and implemented long after the line is in service. The main measures that are carried out in

• Exchange the old equipment that can be affected by new equipment immune against

• Provide ways of protecting the existing services changing only parts of it (usually

changing environment.

order to lessen the effects of the disturbances.

**2. Description of the problem** 

order to lessen or avoid these problems are:

wires) immunizing the system against disturbances.

disturbances.

field.

There are different effects of the disturbances that affect different victims. Victim is the usual term while talking about electrical disturbances for the affected element. Disturbances can be grouped into two main groups:


The term noise is used when the effects of the disturbance can cause malfunction of the equipments. When the disturbance can affect human health or can provoke a fail against safety, the usual term is safety hazard. The victims of these disturbances are also different ones:


Usually radiated disturbances are related to quite high frequencies in usual EMC treatises but in this case and due to the high power consumption – up to 8MVA for each high speed train – and the antenna like structure of the railway line that make it possible to emit 50 Hz electromagnetic disturbances and to be affected by them in the case of the conventional lines fed in DC.

Crossings between high speed lines and conventional lines are another special disturbance point. The angle of the crossing have a special relevance since the small this angle is, the more effect will have in disturbing the already existing systems, while if the cross is right angled the effects of the disturbances will be almost negligible.

Since a way to lessen current return by earth in DC configurations is to isolate the rail from earth, high voltages can appear between the rail and earth. This problem can also appear if railway lines are fenced. If the fence is not properly earthed, high induced voltages can appear between fence and earth. In DC lines shielded cables are used, but they are often earthed in just one edge in order to avoid DC return through them finding a less impedance way back to the feeder station. This way of earthing wires is effective against electrostatic disturbances (capacitive coupling). Electrostatic field does not disturb the wires inside the shielding, but this way of shielding does not protect against induced electromagnetic fields (inductive coupling). This problem has to be carefully identified because a compromise between inductive coupling and DC current return by the shielding earthed in both extremes of the wire.

Another problem in order to determine the effects of the disturbances is to identify the currents that can flow through the high speed line overhead wire system. This is not an easy task since signalling and electrification branches in major railway infrastructure management companies or administrations are not related and obtaining information from the electrification branch from the signalling part can be difficult. So trying to obtain shortcut currents or fault duration is not an easy task for signalling engineers. Determine

Electrical Disturbances from High Speed Railway Environment to Existing Services 165

The resulting induced voltages in the victim system, in absence of protection, can cause hazards to personnel, material deterioration, problems in the proper functioning as

Fig. 1. Coupled inductors and coupled capacitors between the disturbing line and the

To explain the phenomena the induced voltages in a victim wire will be studied. The development will be done considering the generic catenary pole of Figure 2, composed by:

unexpected operation of railway signaling installations.

disturbed line

• 2 catenary wires; • 2 contact wires • 2 negative feeders; • 2 return current wires;

• 4 tracks (considered as active wires).

Fig. 2. Structure of a catenary pole

these currents will affect – as can be easily seen – to the determination of the boundaries between affected and not affected equipments, facilities or systems. This status quo is changing in the last years, at least in Spain, so current limits are defined taking into account electrification systems information.

Conducted disturbances have a major impact in two aspects: the rise of the voltage between the rail and earth and the disturbances that may cause to the 50 Hz track circuits that might be present in the line. The effects on the track circuit are highly affected by the impedance balance of the two rails. If the impedances of both rails are unbalanced a 50 Hz voltage will appear between the rails and depending on the relative phase between the 50Hz signal of the track circuit and the conducted one the operation of the line (if a false track circuit occupation occurs) or even a failure against safety if a shunted track circuit (occupied) due to the disturbance signal will give a false unoccupied information. CITEF, ADIF and the major Spanish 50Hz track circuits suppliers have carried out test to determine these effects and both of the above related cases can occur depending on the rail impedance unbalance and the relative phase of the signals. The location of feeder stations has also an impact in the distribution of currents along the rail and also affects the propagation of the effects.

These conducted disturbances might appear when a train unit is contacting both lines while crossing through a gauge change facility or a transition zone from AC to DC fed lines or electrified to non electrified lines. The train unit might be fed by AC through the pantograph and some of the returning current might, depending on the train configuration, end returning through the DC rails. In order to avoid this undesired current return isolation rail joints and impedances are used.

There are other signalling systems – like for example electronic block – that might be disturbed by harmonics originated by traction units. Electronic block depending on the used technology can be established between stations using a modulated signal of few kilohertz. Rolling stock modern composition for high speed lines do usually use asynchronous electric engines controlled with frequency shifters in order to enhance the performance and lessen the losses. Asynchronous engines are more efficient for the same weight than other electric engines and very easy to maintain so they are thoroughly used in train units using electronic controllers. These units can emit a series of harmonics that can interfere with such systems as electronic block.
