For describing the voltage of power lines, cables and overhead wires.
For describing the 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.
The ITO Map electricity layer shows power-lines by voltage, allowing for quick analysis of the OSM data. The voltage levels shown are currently designed with the UK power grid in mind, but at a minimum the layer will still show whether a voltage=* is present or not.
How to get the voltage of a line/cable without touching it? Simple safety rule for transmission lines is this. The length of the isolator (separating wires from tower) is 1 meter per 100 000 Volt. 380 kV wires have isolators of ~4 meters long. Following this rule a 25 kV overhead wire use 0.25 m long isolators.
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.
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 corrision. 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 thecurrent 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.