- #1
Charles123
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Why Single-wire Earth return systems are only used in rural areas? Why not also in urban areas where there is only demand for single phase power?
Why Single-wire earth return systems are only used in rural areas?
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Discussion Overview
The discussion centers around the use of Single-wire Earth return (SWER) systems, specifically why they are predominantly employed in rural areas rather than urban settings, despite the potential for single-phase power demand in cities.
Discussion Character
- Debate/contested
- Technical explanation
- Conceptual clarification
Main Points Raised
- Some participants suggest that cost is a primary factor for using SWER systems in rural areas, as they require only one copper conductor instead of two.
- Others argue that the question remains why this system is not also applied in urban areas where single-phase power is needed.
- One participant posits that in rural settings, the single wire feeds a transformer at each isolated farm, with the return path through the Earth, which may incur losses compared to a copper return.
- Another participant notes that urban areas typically have higher total loads, necessitating balanced three-phase systems, which require a neutral wire for effective operation.
- It is mentioned that in urban settings, it is often more economical to install multiple wires rather than individual transformers for each dwelling.
- One participant clarifies that while SWER pertains to the primary circuit, each customer still has a neutral wire in the secondary circuit from the transformer to their building.
- Concerns are raised about the voltage drop across the Earth return in urban areas due to higher current draws, which could lead to significant voltage regulation issues.
Areas of Agreement / Disagreement
Participants express multiple competing views regarding the applicability of SWER systems in urban areas, with no consensus reached on the reasons for their limited use outside rural contexts.
Contextual Notes
Participants highlight various assumptions regarding the efficiency and practicality of SWER systems, including the impact of current draw on voltage drop and the maintenance of grounding connections over time.
- #2
davenn
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Primary reason I would assume would be cost... you only pay for one copper conductor NOT 2 same as they used to do for out of the way rural phone lines
Dave
Dave
- #3
Charles123
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Of course that would be the main reason for using it, that`s why the question is why not also in urban areas where there is only demand for single phase power?
- #4
NascentOxygen
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I'll venture a guess, to see whether anyone can shoot this down. 
I seem to recall seeing in rural areas that the single wire feeds a pole-mounted transformer as it passes each isolated farm. The mains return is via an Earth at the power pole, and from the transformer the farmer gets both active and neutral wires. I would expect Earth return to involve appreciable losses, compared with copper return.
So, extending this to suburban areas, almost every power pole would have to incorporate a transformer and a buried Earth return, if we were to avoid twin wires running along the streets.
I seem to recall seeing in rural areas that the single wire feeds a pole-mounted transformer as it passes each isolated farm. The mains return is via an Earth at the power pole, and from the transformer the farmer gets both active and neutral wires. I would expect Earth return to involve appreciable losses, compared with copper return.
So, extending this to suburban areas, almost every power pole would have to incorporate a transformer and a buried Earth return, if we were to avoid twin wires running along the streets.
- #5
Windadct
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This was done for cost - and typically old farm houses used very little power. Really there are 2 conductors missing - a Neutral and a Ground - I do not know if they will allow this type of install today - but they used to then make a secure Earth connection ( Grounding rod ) Really every installation has one, but in this single line type connection the ground rod is actually conducting current.
The Grounding rod actually can have relatively low resistance - back to the pole, ~1 Ohm - but the real issue is that the grounding rod will deteriorate over time - high rate of corrosion due to the current - so this connection needs to be checked and maintained.
In Urban or more densely populated areas the total load is greater and the utility will try to maintain balanced 3 phase loads in their system, but also one transformer will be feeding many customers - typically the transformers in an area will be matched and to do this well they need a neutral. Also - modern feed is 240/120 ( here int he USA) - split phase - this also requires the neutral.
The Grounding rod actually can have relatively low resistance - back to the pole, ~1 Ohm - but the real issue is that the grounding rod will deteriorate over time - high rate of corrosion due to the current - so this connection needs to be checked and maintained.
In Urban or more densely populated areas the total load is greater and the utility will try to maintain balanced 3 phase loads in their system, but also one transformer will be feeding many customers - typically the transformers in an area will be matched and to do this well they need a neutral. Also - modern feed is 240/120 ( here int he USA) - split phase - this also requires the neutral.
- #6
256bits
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This Wiki article explains the system.
http://en.wikipedia.org/wiki/Split_phase
You see that the rural residant obtains 2 live wires and a third neutral line that go into his fuse panel. By selection of proper terminals, he/she can have 120 v for lighting and outlets, and 240 v for stoves, dryers just like an an urban residant.
The neutral line could carry a current depending upon how the electrical balance was set up from the fuse panel for circuiitry in the house or other farm building. A ground wire for safety reasons could be set up from the fuse box to the Earth ground.
The main reason for this setup was cost of one wire versus 2 for a long transmission line. And with one resident per transformer, load balance was not that much of a problem. In urban areas, the reverse is true - it is less costly to set up more wires than have a transformer for each dwelling - imagine 10 transformer units on a pole for a 10-unit apartment building.
http://en.wikipedia.org/wiki/Split_phase
You see that the rural residant obtains 2 live wires and a third neutral line that go into his fuse panel. By selection of proper terminals, he/she can have 120 v for lighting and outlets, and 240 v for stoves, dryers just like an an urban residant.
The neutral line could carry a current depending upon how the electrical balance was set up from the fuse panel for circuiitry in the house or other farm building. A ground wire for safety reasons could be set up from the fuse box to the Earth ground.
The main reason for this setup was cost of one wire versus 2 for a long transmission line. And with one resident per transformer, load balance was not that much of a problem. In urban areas, the reverse is true - it is less costly to set up more wires than have a transformer for each dwelling - imagine 10 transformer units on a pole for a 10-unit apartment building.
- #7
Charles123
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Thank you for your answer!
- #8
ajaynejr
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Single wire Earth return pertains only to the primary (19 kv, etc.) circuit from the substation. Each customer still has a neutral wire (grounded/earthed conductor) in the respective secondary circuit from the pole transformer to the building fuse/breaker panel.
In a SWER system one pole transformer can also server multiple customers.
In rural areas the overall amount of current drawn by the primary circuit (at primary circuit voltages) is usually small enough that the voltage drop across the Earth return is not too great. If the current draw got too large for the Earth conductivity, as would happen in an urban or suburban setting, then the primary voltage and therefore the customers' secondary service voltage would drop noticeably. Because the current draw could vary greatly over the course of a day or even an hour, automatic voltage regulation would be needed.
In a SWER system one pole transformer can also server multiple customers.
In rural areas the overall amount of current drawn by the primary circuit (at primary circuit voltages) is usually small enough that the voltage drop across the Earth return is not too great. If the current draw got too large for the Earth conductivity, as would happen in an urban or suburban setting, then the primary voltage and therefore the customers' secondary service voltage would drop noticeably. Because the current draw could vary greatly over the course of a day or even an hour, automatic voltage regulation would be needed.
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