# Key:voltage

Description v · d · e voltage For describing the voltage of power lines, cables and overhead wires. Group: Power frequency=* power=transformer Q25428 Status: in use taginfo · GB · IE · IN overpass-turbo

For describing the nominal voltage of any high voltage power line and cable. This can be high-voltage transmission line or even a overhead wire of train tracks, or on a street for trolley busses. Used for e. g. powerlines and railway electrification.

Any value should be in Volts without unit itself and without thousand note/delimiter. Value for a 15 kV wire is “15000”. Not “15 kV”, nor “15,000” or combinations of this.

Open Infrastructure Map shows power lines colour coded by voltage range and its exact value, allowing for quick analysis of the OSM data.

Voltages can be safely determined through signage on the support structures (or signs on sites where underground cables run), or the length of insulators used (using the latter is more difficult, as it takes knowledge of the grid voltages used).

For a substation (power=substation) stepping up or down between different voltages, the voltages can be listed, separated by semi-colons.

## Nominal/Rated/Maximum Voltages

There is some disagreement between system operators about "nominal" line voltages. A line which is classified 400 kV in the UK and a one which is classified as 420 kV in continental Europe may be carrying very similar levels of voltage in practice - it is only the nominal voltage designation which is different.

In some areas the "nominal" voltage publicised may actually be the maximum continuous rated voltage, especially as methods for regulating voltage improve so lines can be run closer to their theoretical maximum.

There's no easy way of finding out the actual levels of voltage, so the system operator's designation should be used, but it should be noted that these "nominal" voltages aren't directly comparable between countries.

## Examples

A high-voltage transmission line with a voltage of 110 kV would use the following keys and values.

An electrified railway track in Germany with overhead power supply would use these keys and values.

Nearly the same for a subway with separate rail for power supply.

A street with overhead wires for trolley busses.

A distribution substation, stepping-down voltages for use by houses.

## HVDC-systems

Some HVDC-systems use the earth or a grounded conductor as return. Not only monopolar HVDC-schemes use such a device, it can be also found at many bipolar HVDC-schemes in order to allow an operation of the scheme in monopolar mode, however in most cases with reduced power. The grounded conductor must be always installed with insulators on the support structures as uncontrolled ground currents lead to undesired electrochemical corrosion. The grounding must be performed therefore with specially designed grounding electrodes, situated and designed so, that no electrochemical corrosion occurs.

The grounded conductor, which is called electrode line, when it runs from a converter plant to a grounding electrode, can but must not be mounted on the towers carrying the high-voltage poles of the HVDC-scheme. It can also run on a separate line or fixed on towers of AC-lines. As it runs into a ground electrode, it can serve as ground wire, whereby the insulators must be equipped with lighting arrestors.

If the towers of an HVDC-line carry also a conductor used as grounded return, the voltage must be described with “HVDC-voltage ; 0”, if not than set just the HVDC-voltage. For AC-lines carrying a grounded return conductor of an HVDC-scheme, set as voltage “AC-voltage(s) ; 0” and as frequency “AC-frequencies ; 0”.

Ground return conductors of HVDC-schemes must be always considered at cable count.

The voltage value 0 for such lines is strictly spoken not correct. In fact, it shows a voltage against ground which is equal to the product of the line current and the sum of ground resistance and resistance of line to grounding point, but as the current value depends on the load and resistance values are often not available, the value 0 is a good choice as it implies, it is grounded.