Number of electrical circuits in a power line or cable connection
Use circuits=* to note the number of electrical circuits of a transmission line or cable connection. The tag is primarily intended for underground cable connections where the number of physical cables is unknown or has no simple relationship with the number of circuits.
In power transmission a circuit consists of the conductors needed to allow current to flow from a power source to the load and back to the source. Think of a battery and a load such as a light bulb connected by two wires. Current will flow from the battery to the load via the positive wire and return to the battery via the negative wire. For three-phase AC power transmission things are slightly more complex as three different AC currents flow in the three conductors forming a circuit. The currents flowing in the three phase conductors will tend to cancel out one another and unless there is an additional neutral conductor the net current will be zero.
One-phase AC transmission systems are also known. One example is traction power systems for railways using two-conductor one-phase transmissions. Sometimes one-phase systems require just one metallic conductor by using earth as the return conductor. Examples are Single Wire Earth Return systems used in some rural areas and monopole HVDC connections using earth or seawater as the return path.
When to use
The circuits=* tag should be used in the following situations.
- Underground or underwater cable connections (power=cable). The cables=* tag is useless for calculating the number of circuits here since the number of physical cables per circuit varies (typically 1, 3 or 6 cables per circuit). Furthermore the number of physical cables is often unknown to the mapper.
- Overhead power lines (power=line) in the following situations:
- The number of conductors (cables) is not a multiple of three.
- Two apparent circuits (2 * 3 cables) are operated as one effective circuit. This means that the two circuits are wired in parallel and connected to a single bay in the substation.
Otherwise this tag is not needed for overhead power lines as the number of circuits can be derived from the cables=* tag.
How do you know the number of circuits? If an overhead power line connects to an underground cable connection at a cable transition tower the number of cable circuits will normally be equal to the number of power line circuits (one-third the number of cables). When the connection between two substations is entirely underground the data may sometimes be available in public information from the grid operator. However verify that such information is available under a license that is compatible with the ODbL license before using it!
Please note that this tag should not replace the cables=* tag.
|Power line transition to underground cable connection. It is not clear to a non-expert mapper whether two three-phase cables or six single-phase cables are used here. However, it is directly visible that the cable connection comprises two circuits.|