Regulation for Electrical Railway Track Crossings

The required vertical distance between the lowest power line conductor and the railway track, varying based on voltage.

Power lines crossing railway tracks below ground up to 11 kV.

Power lines crossing railway tracks below ground, recommended for voltages up to 33 kV.

The power line crossing the railway track should ideally be perpendicular or nearly so.

The ideal angle for overhead powerline crossings.

Crossing at an angle not more than 30 degrees when necessary.

Authorization for power line crossings deviating from standards.

Electrical inspectors can approve lower heights if space constraints and costs make it difficult.

The base height for overhead power lines of 11 kV to 66 kV is 14.10m.

The transmission line height for powers ranging from 400 kV to 800 kV is 23.4m above the rail.

The required distance between power lines and other objects to ensure safety during maintenance and operation.

The minimum distance between a guard wire and the highest traction conductor, for safety purposes, during powerline crossing.

Voltage induced in a distribution system due to current flowing in adjacent high voltage power lines.

Current induced in a distribution system caused by capacitive coupling with nearby high voltage power lines, due to electrostatic interactions.

The acceptable level of electromagnetically induced voltage, based on access restrictions: 60V for authorized personnel; 25V for public access.

The maximum allowable electrostatically induced discharge current to avoid electrical shock.

The neutral of a 3-phase, 4-wire earthed system should be connected to earth at only one point (the substation).

For long metallic structures (such as fences or overbridges), EMIV should not exceed 25 volts.

The formula for calculating electromagnetically induced voltage is E = 2π.Kr.Kc.M.I.L.

Maintain a minimum of 2 meters of physical space around a 25kv system to ensure maintenance personnel safety.

The voltage rise (E) in an overhead power line due to induction is calculated using the formula: E = 2 * π * f * kr * Kc * M * I * L. Where:

• E is the voltage rise in volts
• f is the frequency of the power supply (usually 50Hz)
• kr is the coefficient based on return circuit type and rail availability (SNCF values available)
• Kc is the cable screening factor (1 for bare conductor, 0.8 for sheathed cable)
• M is the mutual inductance in Henry, affected by conductor-earth distance and earth resistivity
• I is the current in the OHE in amperes
• L is the length of parallelism in meters

kr is a coefficient reflecting the type of return circuit and the availability of rails for traction current. It has been empirically established by SNCF and its values vary based on the number of rails available for traction current and whether the track is single or double.

Kc represents the cable screening factor, which accounts for the type of overhead conductor used. It is 1 for a bare conductor and 0.8 for a lead sheathed underground cable.

M stands for mutual inductance, which is measured in Henry. It quantifies how strongly the magnetic fields of the OHE and the return path interact. It's influenced by the distance between the conductors and the earth's resistivity.

The length of parallelism (L) of an overhead conductor is measured by projecting its path onto the alignment of the OHE. This means the distance between the OHE and the conductor is averaged along the track.

Table 9.1, empirically derived by SNCF, gives voltage rise values for specific conditions: double track OHE, 600A current, earth conductivity of 8x10^-2 S/m. These values are considered safe for most conditions, as earth conductivity is usually higher.

For a single track OHE with only one rail available for return current, the voltage rise obtained from Table 9.1 needs to be adjusted. Since the maximum current is 300A (half of the double track value), divide the value obtained for the relevant length of parallelism by 2.

Earth conductivity plays a role in the mutual inductance (M), which affects voltage rise. Higher conductivity leads to a lower M value, reducing the voltage rise. Table 9.1 is based on an assumed earth conductivity of 8 x 10^-2 S/m, which is typically lower than actual values, ensuring safe results.

The coefficient 'kr' in the voltage rise formula accounts for the return path and the availability of rails for traction current. Different configurations of the return circuit have varying levels of inductance, affecting the voltage rise. Therefore, considering these factors ensures accurate and safe calculations.

The adjustment factor for calculating induced voltage in single-track, single-rail sections is 0.69, used to account for the single return path.

The adjustment factor for calculating induced voltage in double-track, double-rail sections is 0.39, reflecting the multiple return paths.

Using booster transformers and return conductors significantly reduces induced voltage, requiring adjustments for accurate calculations.

The reduction in voltage rise due to booster transformers depends on their spacing. A spacing of 2.66 km divides the value by 2.3, while 4 km spacing divides by 1.7.

The length of the overhead line running parallel to the electrified track significantly influences induced voltage calculations.

The average distance between the overhead line and the electrified track is a crucial factor in determining induced voltage.

When calculating induced voltage, it's important to consider the return path for traction currents. The number of rails available for this purpose impacts the result.

Induced voltage must remain within safe limits to avoid detrimental effects. If exceeding the limit, remedial actions are necessary.

Various methods can be employed to reduce induced voltage, including shifting feed points, sectionalizing lines, installing auxiliary transformers, or relocating the distribution line.

Using lead or aluminium sheathed cables for the overhead line can effectively minimize induced voltage.

Power lines crossing railway tracks must be cabled and placed underground for voltages up to and including 11kV.

Crossing railway tracks with power lines up to 33kV is recommended to be done using underground cables.

Overhead power line crossings must maintain a minimum vertical clearance above rail level, varying based on voltage.

Kr is a coefficient representing the type of return circuit and rail availability, impacting induced voltage calculations. It is determined empirically.

The voltage reduction with booster transformers depends on their spacing. Closer spacing has a larger impact.

The voltage rise (E) in an overhead power line due to induction is calculated using the formula: E = 2 * π * f * kr * Kc * M * I * L.

The minimum distance required between overhead power lines and other objects (like railway tracks) for safety and operational reasons. This distance varies based on the voltage of the power line.

A phenomenon where a changing magnetic field from a nearby power line induces a voltage in an adjacent electrical distribution system.

When a high-voltage power line creates an electric field that induces a discharge current in a nearby system due to capacitive coupling.

The neutral wire in a three-phase, four-wire earthed system should be connected to ground (earth) at only one point, typically at the substation.

The maximum acceptable level of EMI voltage in long metallic structures, such as fences or overpasses, is typically 25 volts.

The formula to calculate voltage rise in an overhead power line due to induction from traction current is: E = 2π * f * kr * Kc * M * I * L. E is the voltage rise in volts, f is the frequency, kr is a coefficient based on the return circuit, Kc is the cable screening factor, M is the mutual inductance, I is the current, and L is the length of parallelism.

'Kc' reflects the type of overhead conductor used. It's 1 for a bare conductor and 0.8 for a lead sheathed underground cable. A sheathed cable shields the electricity better, reducing its influence on the surrounding environment.

The length of parallelism (L) is the section where the overhead conductor runs parallel to the electrified track. It's measured by projecting the conductor's path onto the alignment of the OHE. This gives the average distance between the OHE and the conductor.

The voltage rise for a double-track OHE with all four rails available for traction current is usually calculated first. To adjust for single track scenarios where only one rail is available for return current, the value obtained for the corresponding length of parallelism needs to be divided by 2.

Earth conductivity significantly influences the mutual inductance ('M'), which in turn affects the voltage rise. A higher conductivity leads to a lower 'M' value, reducing the voltage rise. The voltage rise values provided are safe for most conditions because they are typically based on earth conductivity that is lower than what's usually experienced.

'kr' is vital because it reflects the differences in the return path's configuration and the rails available for traction current. Different configurations of the return circuit have varying levels of inductance, influencing the voltage rise. Therefore, considering 'kr' ensures accurate and safe voltage rise calculations.

Various strategies can be used to reduce induced voltage, such as shifting feed points, sectionalizing lines, installing auxiliary transformers, or relocating the distribution line. Utilizing lead or aluminum sheathed cables for the overhead line can also significantly minimize voltage rise.