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You are here: Home / Policy / SAGE / SAGE First Interim Assessment / SAGE recommendations on phasing

SAGE recommendations on phasing

This page discusses one of the recommendations from SAGE's First Interim Assessment.  See also more on SAGE generally and on the First Interim Assessment.

Where overhead lines have two circuits, there is a choice about how they are wired relative to each other, called the "phasing". One option, usually a phasing known as "transposed", results in more cancellation between the two circuits and lower fields. More on "phasing" including graphs showing this effect.

SAGE says:

"We recommend that electricity companies be encouraged to choose the optimal phasing (usually transposed phasing) for all new lines, and also be encouraged to convert existing lines where possible and justifiable."

And also

"We do not expect our recommendation to result in any change for the National Grid"

This is because the National Grid (400 kV and 275 kV lines) was built from the start with a policy of using transposed phasing where possible. About 90% is already transposed. The remainder is mainly made up of single-circuit lines, where phasing is not relevant, or situations where three lines meet at a "T" point, where it is infeasible to achieve transposed phasing for all three lines.

For 132 kV lines, SAGE collected rough estimates from electricity companies. Between 70% and 90% (depending on the company) of lines are double-circuit as opposed to single-circuit. Of these, between 70% and 90% were estimated as already transposed. SAGE estimated that 12% of 132 kV lines, 2000 km, are not currently transposed but reasonably could be.

Resulting from SAGE's recommendation, there is now a formal policy on phasing in the UK, and this has led to the electricity industry collecting and reporting more accurate statistics.  We now know that 50% of double-circuit 132 kV lines have optimum phasing.

SAGE estimates the cost of converting a line to transposed phasing as £60k for 275 kV and 400 kV lines or £10k - £30k for 132 kV lines, where it can be done simply by changing the terminations at the end of the line. If it cannot be done that way and requires a new pylon or other new work the cost rises.

SAGE says:

"We do not advocate a rigorous definition of what should be done, nor do we believe it should be enshrined in regulation or should have a specific timescale attached. Instead, we consider this will be most effective if expressed as a general encouragement to electricity companies to take the desired action where possible."

Government response

In October 2009, the Government formally responded to SAGE's recommendations.  See full details of the response.  On this particular issue of phasing they said:

"The Government agrees with the SAGE recommendation and urges industry to optimal phase overhead lines wherever possible and reasonable. We will proactively work with industry to consider how best to take this forward. This might include developing a voluntary code of practice on phasing for voltages of 132kV and above." (para 50)

That Code of Practice was duly adopted in February 2011.

See also:

 

  • More on SAGE generally and the First Interim Assessment
  • More on phasing

Latest news

  • New publication on cancer incidence from the UK electricity industry Cohort Study August 27, 2019
  • How has the reported risk for childhood leukaemia changed over time? February 11, 2019
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  • New studies on leukaemia and distance from power lines June 1, 2018
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Navigation
  • What are EMFs
    • Terminology – an introduction
    • Electric fields
    • Magnetic fields
    • Units for measuring EMFs
    • Measuring and calculating EMFs
      • “EMF Commercial”
    • Adding fields together
    • Radiofrequencies
    • Screening EMFs
  • Sources
    • Overhead power lines
      • Fields from specific power lines
        • 400 kV
        • 400 kV – specific cases
        • 275 kV
        • 132 kV
        • 66 kV
        • 33 kV
        • 11 kV
        • 400 V/230 V
        • Replacing a 132 kV line with a 400 kV line
      • Summaries of fields from all power lines
      • Factors affecting the field from a power line
        • Voltage
        • Current
        • Clearance
        • Height above ground
        • Conductor bundle
        • Phasing
        • Balance between circuits
        • Balance within circuit
        • Ground resistivity
        • Two parallel lines
      • Calculating and measuring fields from power lines
        • Geometries of power lines
        • Raw data
        • On-line calculator
      • Fields from power lines – more detail on the physics
        • Field lines from a power line
        • The direction of the field from a power line
        • Power law variations in the field from a power line
      • Statistics of power line fields
    • Underground power cables
      • Different types of underground cable
      • Fields from cables in tunnels
      • Gas Insulated Lines (GIL)
      • Underground cables with multiple conductors
      • Effect of height on fields from underground cables
      • Screening fields from underground cables
    • Low-voltage distribution
      • UK distribution wiring
      • USA distribution wiring
    • House wiring
    • Substations
      • National Grid substations
        • Static Var Compensators
      • Sealing-end compounds
      • Distribution substations
      • Final distribution substations
        • Indoor substations
    • Transport
      • EMFs from electric trains (UK)
      • EMFs from cars
    • Appliances
    • Electricity meters
      • Smart meters
      • Traditional meters
    • Occupational exposures
      • Live-line work
      • Static Var Compensators
      • Occupational exposures on pylons
    • Field levels and exposures
      • Personal exposure
      • Other factors that vary with magnetic fields
      • Fields greater than 0.2 or 0.4 µT
    • Screening EMFs
      • Screening fields from underground cables
      • EMF Reduction Devices
  • Known effects
    • Induced currents and fields
    • Microshocks
      • Control of microshocks in the UK
      • Microshocks from bicycles
      • Bees and microshocks
    • EMFs and medical devices
      • Standards relating to pacemakers and other AIMDs
    • Effects of EMFs on equipment
  • Research
    • Types of research
    • Epidemiology
    • Animal and laboratory experiments
    • Mechanisms
    • Specific studies
      • UKCCS
      • CCRG
      • French Geocap study
      • CEGB cohort
      • Imperial College study
  • Current evidence on health
    • Childhood leukaemia
      • Survival from childhood leukaemia
      • Childhood leukaemia and Downs
      • Childhood leukaemia and night-time exposure
      • The “contact current” hypothesis
    • Other health effects
    • Scientific review bodies
      • WHO
      • IARC
    • Electric fields and ions
    • Comparing EMFs to other issues
  • Exposure limits for people
    • Limits in the UK
    • Limits in the EU
    • Limits in the USA
    • Limits in the rest of the world
    • Limits from specific organisations
      • ICNIRP 1998
      • ICNIRP 2010
      • NRPB 1993
      • NRPB 2004
      • EU 2004
      • EU 2013
  • Policy
    • UK policy
      • Power lines and property – UK
    • Compliance with exposure limits
    • European EMF policy
    • Precaution
    • SAGE
      • SAGE First Interim Assessment
        • Government response to SAGE First Interim Assessment
      • SAGE Second Interim Assessment
        • Government response to SAGE Second Interim Assessment
        • SAGE Second Interim Assessment – the full list of recommendations
  • Finding out more
    • EMF measurement and commercial services
    • Links
    • Literature
    • Contact us
  • Static fields
    • Static fields – the expert view