**6. Measurements methodology**

CITEF has performed several measurements campaigns in order to determine whether the systems and facilities used in conventional lines described above are well protected against disturbances or not. A measurement methodology was used and will be presented here. This methodology has been enhanced with the experience acquired and the analysis of the results. Measurements were carried out in the following elements:


In order to obtain good accurate results a pole is disposed in a determined position of the high speed line to shortcut the electrical overhead wire system and the rail. Calculations are made in order to determine that point considering the position of the feeder stations, the impedance of the rail and the impedance of the overhead wires. 1x25 kV scheme is adopted even if electric trackside facilities are 2x25 kV. This is made so because this electrification scheme is more disturbing and return impedance is higher. This is done this way in order to obtain a steady state current as close as possible as 1200 A. This current is determined by the estimated amount of energy needed when two double train compositions accelerate at full throttle simultaneously in the same electrical section. This is an ADIF (Spanish Railway Infrastructure Manager) requirement. Sometimes because of the topology of the line, the situation of the feeder stations and the electric network, that current level cannot be obtained. In that case, lower currents are considered and measured.

In order to determine the position of the short-circuit pole, calculations are performed using a CITEF self developed application that implements these electrical calculations, but this calculations can be estimated easily knowing the impedance of the elements (rail and overhead contact line), the voltage level in the feeder station and the position of the feeder stations in the line.

There are other elements that have similar problems like the wire fences used to prevent intrusions in high speed lines. Also metal structures in big stations like metallic shelters that are not adequately earthed can have accessible voltages that have to be measured in order to

In order to keep the accessible voltage or the touch voltage below the established limits, and as is reflected in the standard EN 50122-1, voltage limiting devices (VLD) can be connected between earth and rail, fence or structure. These devices keep both parts isolated from each other until the voltage between them exceeds a certain defined value, then it connects both parts so there is an electrical circulation between both systems and after that the VDL opens

Another solution that cannot be used for rails is to have a good earthing circuit. Metallic shelters or metallic fences should be adequately connected to earth in order to prevent

CITEF has performed several measurements campaigns in order to determine whether the systems and facilities used in conventional lines described above are well protected against disturbances or not. A measurement methodology was used and will be presented here. This methodology has been enhanced with the experience acquired and the analysis of the results.

• 50 Hz track circuits placed in the boundary section between 50 Hz track circuits

• Communication wires between stations. They are measured at each end of the electrical

• Signal aspects. In this position, a lit aspect and a switched off aspect are measured in

• Touch voltage in the metallic elements like fences, signal posts, point engines, lampposts, etc. surrounding the measurement position and of the rails according to EN

In order to obtain good accurate results a pole is disposed in a determined position of the high speed line to shortcut the electrical overhead wire system and the rail. Calculations are made in order to determine that point considering the position of the feeder stations, the impedance of the rail and the impedance of the overhead wires. 1x25 kV scheme is adopted even if electric trackside facilities are 2x25 kV. This is made so because this electrification scheme is more disturbing and return impedance is higher. This is done this way in order to obtain a steady state current as close as possible as 1200 A. This current is determined by the estimated amount of energy needed when two double train compositions accelerate at full throttle simultaneously in the same electrical section. This is an ADIF (Spanish Railway Infrastructure Manager) requirement. Sometimes because of the topology of the line, the situation of the feeder stations and the electric network, that current level cannot be

In order to determine the position of the short-circuit pole, calculations are performed using a CITEF self developed application that implements these electrical calculations, but this calculations can be estimated easily knowing the impedance of the elements (rail and overhead contact line), the voltage level in the feeder station and the position of the feeder

pairs or quads and loaded with the characteristic impedance of the line.

order to determine whether or not are affected by disturbances.

50122-1 Annex E: Measurement methods for touch voltage.

obtained. In that case, lower currents are considered and measured.

check that there are not over the limits established by the standards.

the circuit and checks the voltage between both parts.

Measurements were carried out in the following elements:

unmodified and audiofrequency track circuits.

accidents or electrocutions.

stations in the line.

**6. Measurements methodology** 

The use of this shortcut steady state current is of great value in order to assure the repetitiveness of the measures. A real traction unit won't allow a steady state current to be maintained in order to measure the effects in the determined elements.

To measure touch voltage the **EN 50122-1 Annex E methodology** is used. The methodology described in the standard can be summarized in the following aspects:


In order to perform the measures a quad is used. This quad is loaded in the determined ends with the characteristic impedance of the wire that is usually a value between 500 to 600 Ω depending on the wire. These measures are carried out with the shielding of both ended connected and with one of the ends unconnected in order to determine the disturbance induced when the shielding in not properly connected.

These measures are usually done by two measurement teams each one of them placed at each one of the ends usually in a station communication facility. In order to comply with the measurement procedure a continuity of the shielding from one end to the other of the wire needs to be achieved. This was not always possible because DC stray currents could be a more important problem than preventing AC disturbances. In these cases, only prevention against electrostatic field was achieved since only one end of the shield was correctly earthed while the other end was unconnected.

The differentiation between electromagnetic shield and electrostatic shield needs to be clarified. In order to prevent electromagnetic disturbances both shields must be connected between them and connected to earth according to the standard **ITU K14 Provision of a metallic screen in plastic-sheathed cables.** The electrostatic shield is just a copper conductor. It is enough to earth just one end of the shield to prevent electrostatic disturbances.

When measures were carried out in a 50 Hz track circuit the measured values were:


These measures should be carried out shunting the emitter and without shunting it in order to determine the disturbance in both situations. As said before, one of them –occupancy of an unoccupied track circuit- has operational implications and the other one –liberation of an occupied track circuit- has safety implications.

Electrical Disturbances from High Speed Railway Environment to Existing Services 181

Fig. 10. Graphical representations of the measurements around one signal

measurement items nearby a signal the measured items were:

have to be protected against direct contact.

• Signal (blue) • Point engine (red) • Fence (green) • Pole (yellow) • Farther rail (purple) • Nearer rail (pale green)

**8. Conclusion** 

For Figure 9 current values, Figure 10 offers the registered values for a series of

Some of the items measured had a 10/1 reduction probe. In this case both rails have this relation. This example shows in a very visual way that the effects described in the above sections do occur. These items were measured according to the EN 50122-1 described methodology and some of the obtained values overpass the limits described in the standard. This example shows in a very clear way that the effect does exist and that measures have to be adopted in order to prevent their effects. That figure shows the effect in elements that

Electrical disturbances are close related to power quality, and service quality, and even safety, can be seriously compromised when two linear systems with different electrical

And the measured rms values were:

• Signal: negligible (0V) • Point engine: 1,1 Vrms • Fence: 114,9 Vrms • Pole: 85,4 Vrms • Farther rail: 46,4 Vrms • Nearer rail: 46,6 Vrms

Fig. 8. Measurement scheme for communication wires used in the measurement campaigns by CITEF
