|
Here you see the so called "S(ingle) W(ire) E(arth) R(eturn)" system. This system is used throughout the world, but mainly in New Zealand and Australia.
When looking at the secondary side of a high voltage step down transformer (e.g. 33 to 12,7 kV); using a conventional phase-neutral or phase-phase transformer system, 2 wires are needed to have a closed circuit.
With a SWER system, on the secondary side, the neutral or second phase wire is replaced with an earth stake. This leaves only the remaining phase wire which needs to brought to the distribution/service transformer, which is meant for customer use (low voltage).
But with only 1 wire, there's no closed circuit, right?
This is solved by placing earth stakes at the distribution/service transformers.
The remaining phase wire, from the secondary side of the high voltage step down transformer, is connected on the primary side of the distribution/service transformer. The other primary connection is connected to an earth stake. When the earth stakes are properly placed (deep into the ground with enough groundwater), the connection is very low ohmic. This means the earth stakes are used as the returning wire (neutral or second phase) from the distribution/service transformer to the high voltage step down transformer, making a closed circuit.
The main usage is for rural (country side) electrification. It lowers the costs for long supply lines, by excluding a return wire.
In this circuit there's a 33 kV generator on the left, with a switch. When switched on, the blue line shows 33 kV in the meter.
After the first (high voltage step down) transformer, the SWER system is shown with the earth stakes (no neutral/second phase wire) to the other 2 (distribution/service) transformers. Both transformers contain a switch. The green line will show 12,7 kV in the meter, when the switch is on.
The 2 distribution/service transformers have a split-phase system on their secondary sides of 120/240 V. The orange line is 120 V.
|
