**1. Introduction**

160 Electrical Generation and Distribution Systems and Power Quality Disturbances

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New high speed lines are becoming more and more frequent. These new lines due to their power needs are constructed with a new electric system in order to be able to meet the power demands of the rolling stock and to lessen the electrical losses of the system. There are special cases like the Spanish one where new lines are built in parallel with the existing ones due to lack of space when entering populated zones. This line deployment is more usual in the access to the railway stations in big cities. In this case both lines interfere with each other for several kilometres. The Spanish case is especially interesting because both railway systems work together and there are also points of rolling stock transference between both lines due to the gauge changing facilities and train units that allow trains to operate in both systems.

The main cause of electrical disturbances for the already existing services is the electrification system of the new high speed lines. These lines are electrified with 1x25 kV or 2x25 kV 50 Hz systems. These systems, since they use AC, provoke electromagnetic disturbances in the nearby environment.

The most prone-to-be-affected systems among the existing lines are the track circuits that use 50 Hz for train detection and the wired signalling and telecommunications systems that run in parallel to the railway line.

Track circuits are the most used elements in order to detect train presence in a track section of the line. There are other systems like axle counters that are also used to detect train presence in a section. Most of the deployed track circuits use a 50Hz signal in order to detect the train. Modern track circuits use audiofrequency signals for this purpose and this kind of elements are used in the new built lines, but since is a very reliable safety item there's no need to replace them unless new disturbances can affect this safety related equipment.

The effects of these electrical disturbances can be also affect people. Induced voltages or currents can exceed the limits of the standards or laws. For example **EN 50122: Railway applications. Fixed installations. Protective provisions relating to electrical safety and earthing** defines the limits for AC and DC transients and continuous voltage in the railway environment.

Electrical Disturbances from High Speed Railway Environment to Existing Services 163

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

• Radiated disturbances: these disturbances appear when there's a source of disturbance emits a electromagnetic wave that can be coupled by the victim with the air acting as means of transportation. This is usually called radiated noise in EMC terminology. • Conducted disturbances: these disturbances occur when there's a direct electric contact between the source of disturbance and the victim. This is usually called conducted noise

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

• Communications and signalling equipment: these are mainly affected by sections of

• Detection equipments: these equipments are basically track circuits and these can be

• Rail workers and passengers: people in general can be affected if induced or conducted voltages in the metallic elements that can be accessible are above the limits established

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

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

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

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

be grouped into two main groups:

in EMC terminology.

parallelism and voltage inductions in the wires.

affected both by radiated and conducted disturbances.

angled the effects of the disturbances will be almost negligible.

ones:

by norms.

extremes of the wire.

fed in DC.

The presence of these high speed lines have two main ways of electrical interfering with the so called 'conventional lines'. These interferences can be split into two main blocks:


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 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 order to lessen the effects of the disturbances.

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 field.
