Primarily for Mains power transmission, what voltages, wire configurations and pole types are used to transmit power across the country?

  1. Are three core wires used, with each single wire containing live, neutral, and earth?
  2. Occasionally I see poles with only two cables as oppose to three (three phase), how are these different?
  3. Finally, how is three phase (three cable) converted to single phase for single phase properties?
  • 2
    \$\begingroup\$ Is that Main, Marine or the state of Maine and what countries? Submarine cables to USA? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 13 '18 at 20:05
  • \$\begingroup\$ Wondering what UK and Maine are doing in the same question.... \$\endgroup\$ – Trevor_G Apr 13 '18 at 20:05
  • \$\begingroup\$ Three wires = three phase. Two wires = Single phase. Higher the wire = the higher the voltage. Three phase is split into three balanced single phase circuits with a shared neutral. \$\endgroup\$ – StainlessSteelRat Apr 13 '18 at 20:38
  • \$\begingroup\$ @StainlessSteelRat So with a two wire single phase line, is on the live wire and the other the neutral? Also for the three phase, surely there should be a 4th shared neutral? \$\endgroup\$ – Matt Smallwood Apr 13 '18 at 21:49
  • \$\begingroup\$ Yes. No 4th wire (neutral) needed if loads are balanced. Faults use the earth to activate circuit protection. \$\endgroup\$ – StainlessSteelRat Apr 13 '18 at 22:25

Higher the tower, the higher the transmission voltage. All transmission and the majority of distribution is three-phase (hence multiples of three).

  • Largest steel pylons (275 kV and 400 kV) - Transmission - 3 or 6 cables
  • Smaller steel pylons (132 kV) - Distribution - 3 or 6 cables
  • Wooden poles (11 kV and 33 kV) - Distribution - 3 cables

UK Poles.

Depending on load and remoteness, you also have 66kV and 6.6kV for distribution. Finally stepped-down to 230 (single-phase) /400V (three-phase) for consumers. There are also HV DC Links.

Conductors are uninsulated aluminum conductors with various cores.

9 Players provide power as illustrated by National Electricity Transmission System Performance Report 2016 – 2017.

Transmission/Distribution requires transformers to step-down the higher voltages to lower voltages.
GB Dstributione

They can be wye-wye or delta to delta, but a delta-wye converts from three-phase three-wire to three-phase four-wire. The neutral (Ground in drawing) and each line forms three single-phase 230V circuits (light loads like lights). Feed two single-phase circuiuts to get 400V (heavy loads like stoves/heaters).

Delta to Wye

Power companies go through great effort to balance the load (even as far as reading the obituaries). But at some point remote homes and residential areas do not need three-phase power, so single phase (two wires) or two-phases are used.

Three-phase voltages are phase shifted by 120°, so if the currents are the same, vector addition on currents \$ \overline {I_A} + \overline {I_B} + \overline {I_C} = 0\$. So no neutral is need, which saves copper.

  • \$\begingroup\$ Great! Only slightly confused on why you mean by balancing the load? How does this mean a neutral wire is not needed? Thank you! \$\endgroup\$ – Matt Smallwood Apr 13 '18 at 22:48

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