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  • 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
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        • Static Var Compensators
      • Sealing-end compounds
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    • 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
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  • Static fields
    • Static fields – the expert view
You are here: Home / Sources / Overhead power lines / Fields from specific power lines / 33 kV

33 kV

33 kV double-circuit line:                   33 single-circuit wood pole:
 thumbnail photo of 33 kV wood poles thumbnail photos of 33 kV wood poles

 33 kV lines are either carried on small lattice steel pylons or on wood poles.  There are many different variants of lines design but they all produce roughly similar fields.

All 33 kV lines are inherently compliant with the public exposure limits - see more details

Magnetic field

The maximum field shown here is produced by a lattice pylon design when the ground clearance is the minimum allowed – 5.5 m – and the loads are the highest allowed – not usually above 1 kA in each circuit but there may be exceptions.  The field also depends on the phasing. 33 kV lines usually have Untransposed (U) phasing.

 graph of maximum field 33 kV

Typical fields are lower than the maximum field because the clearance is usually higher and the loads are usually lower.  The two curves shown here are for an estimate of typical loads, 100 A, the normal U phasing, and two different line designs: a lattice steel pylon (the higher field), and a wood-pole design (the lower field).  In practice, when we measure fields from these lines, we find even lower fields, suggesting that 100 A may be an overestimate of typical loads.

graph of typical fields 33 kV

This table gives some actual field values for the same conditions.

     

magnetic field in µT at distance from centreline

maximum under line10 m25 m50 m100 m
33 kVlarger lines on steel pylonsD
single conductors
r=9.8 mm
maximumclearance 5.5 m
phasing U
load 1/1 kA
25.68610.7422.2740.5940.150
typicalclearance 8 m
phasing U
load 0.1 kA
1.5560.8220.2140.0580.015
smaller lines on wood poleswood pole
horizontal array
+-2 m
maximumclearance 5.5 m
single circuit
load .5 kA
14.7482.9610.5410.1380.035
typicalclearance 8 m
single circuit
load 0.1 kA
1.3250.4710.1030.0270.007

Note:

1. All fields calculated at 1 m above ground level.

2. All fields are given to the same resolution for simplicity of presentation (1 nT = 0.001 µT) but are not accurate to better than a few percent.

3. Calculations ignore zero-sequence current.  This means values at larger distances are probably underestimates, but this is unlikely to amount to more than a few percent and less closer to the line.

4. The “maximum field under the line” is the largest field, which is not necessarily on the route centreline; it is often under one of the conductor bundles.

5. Sometimes, a 33 kV circuit could be carried on a line designed for a higher voltage.  Then the magnetic fields could be larger than shown here.

Electric field

The maximum field shown here is produced by a lattice pylon design when the ground clearance is the minimum allowed – 5.5 m.  The field also depends on the phasing. 33 kV lines usually have Untransposed (U) phasing.

graph of maximum field 33 kV 

Typical fields are lower than the maximum field because the clearance is usually higher.  The two curves shown here are for normal U phasing and two different line designs: a lattice steel pylon (the higher field), and a wood-pole design (the lower field).

graph of typical field 33 kV

This table gives some actual field values for the same conditions.

     

electric field in V m-1 at distance from centreline

maximum under line

10 m

25 m

50 m

100 m

33 kV

larger lines on steel pylons

D
single conductors
r=9.8 mm

maximum

clearance 5.5 m
phasing U

897

46

30

10

3

typical

clearance 8 m
phasing U

543

81

21

9

3

smaller lines on wood poles

wood pole
horizontal array
+-2 m

maximum

clearance 5.5 m
single circuit

505

165

16

2

0

typical

clearance 8 m
single circuit

241

147

21

3

0

Note:

1.        All fields calculated at 1 m above ground level.

2.        All electric fields are calculated for the nominal voltage.  In practice, voltages (and hence fields) may rise by a few percent.

3.        All electric fields calculated here are unperturbed values.

4.        All fields are given to the same resolution for simplicity of presentation (1 V/m) but are not accurate to better than a few percent.

5.        Calculations ignore zero-sequence voltages.  This means values at larger distances are probably underestimates, but this is unlikely to amount to more than a few percent and less closer to the line.

6.        The “maximum field under the line” is the largest field, which is not necessarily on the route centreline; it is often under one of the conductor bundles.

7.        Sometimes, a 33 kV circuit could be carried on a line designed for a higher voltage.  Then the electric fields could be larger than shown here.

Underground cables

33 kV underground cables are usually a single cable: the three cores are twisted round each other in a single outer sheath. Because the cores are so close together and twisted, the fields they produce directly are very small.  Instead, the field comes from any net current in the sheath.  This is very variable and cannot be predicted accurately.

The following graph shows typical fields from the net current in a 33 kV cable.

graph of field from 33 kV underground cable 

Occasionally a 33 kV cable may have separate cores.  Then the field would be more like a 132 kV cable with separate cores.

Underground cables do not produce any external electric fields.

This table gives some actual field values for the same conditions.

    

magnetic field in µT at distance from centreline

0 m

5 m

10 m

20 m

33 kV

single cable

0.5 m depth

typical

1.00

0.29

0.15

0.07

Notes

1. All fields calculated at 1 m above ground level

2. All fields are given to the same resolution for simplicity of presentation (0.01 µT = 10 nT) but are not accurate to better than a few percent.

3. These calculations are for a single, isolated cable.  This is rare in practice.  Other nearby cables would modify the field.

Other voltages:

  • 400 kV
  • 400kV special cases
  • 275 kV
  • 132 kV
  • 66 kV
  • 33 kV
  • 11 kV
  • 400 V/230 V

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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