1 / 21

Mark Davies Trevor Charlton Denis Baudin

New Design Methods to Achieve Greater Safety in Low Voltage Systems During a High Voltage Earth Fault. Mark Davies Trevor Charlton Denis Baudin. Mark Davies – UK – Session 2 – Paper 0376. Background.

sheena
Download Presentation

Mark Davies Trevor Charlton Denis Baudin

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. New Design Methods to Achieve Greater Safety in Low Voltage Systems During a High Voltage Earth Fault Mark Davies Trevor Charlton Denis Baudin Mark Davies – UK – Session 2 – Paper 0376

  2. Background • The transfer potential from HV to LV earth electrodes is an important safety consideration, e.g. in UK TNC-S (PME) systems. • UK practice has been to assume that LV transfer potential is simply the worst case soil surface potential, i.e. where it is closest to the HV electrode. This is an overly cautious approach. • A new calculation approach is described and illustrated via case studies. • The work is part of a wider R&D project funded by UK Electricity Distribution Companies via the Energy Networks Association (ENA). Mark Davies – UK – Session 2 – Paper 0376

  3. Existing Calculation Method (UK, ENA ER S.34) The Transfer Potential from the HV Electrode to each LV Rod Electrode is assumed to be equal to the surface potential at the LV Electrode location Transfer Voltage VT(A) = VA VT(B) = VB B A Mark Davies – UK – Session 2 – Paper 0376

  4. Existing Calculation Method (UK, ENA ER S.34) Earth Resistance of a Hemispherical Electrode Surface Potential at distance x from the electrode RHVHV Electrode Earth Resistance (Ω) ρ Soil Resistivity (Ωm) r HV Electrode Radius (m) ICurrent (A) xDistance from HV Electrode where the Surface Potential is Calculated (m) Mark Davies – UK – Session 2 – Paper 0376

  5. Existing Calculation Method (UK, ENA ER S.34) The Transfer Potential from the HV Electrode to a group of LV Rod Electrodes is assumed to be equal to the surface potential at the LV Electrode closest to the HV Electrode B A Transfer Voltage VT(AB) = VA Mark Davies – UK – Session 2 – Paper 0376

  6. VT RA RB VB VA New Calculation Method Equivalent Circuit Accounts for the effect of the surface potential on each LV Electrode and their relative resistances Transfer Voltage B A Mark Davies – UK – Session 2 – Paper 0376

  7. Part of a Project to Improve Safety at 11kV Distribution Substations Mark Davies – UK – Session 2 – Paper 0376

  8. Application of New Calculation Method Mark Davies – UK – Session 2 – Paper 0376

  9. Comparison of Results from Different Methods (CDEGS MALZ) Mark Davies – UK – Session 2 – Paper 0376

  10. Effect of a Low Resistance LV Electrode This LV Rod Resistance reduced to One Fifth of the Others Mark Davies – UK – Session 2 – Paper 0376

  11. Effect of a Low Resistance LV Electrode (MALZ) (MALZ) Mark Davies – UK – Session 2 – Paper 0376

  12. Application to Different Arrangements Mark Davies – UK – Session 2 – Paper 0376

  13. Application to Different Arrangements Mark Davies – UK – Session 2 – Paper 0376

  14. Practical Example – New Residential Development LV Feeder Underground Cables 11kV Distribution Substation HV Electrode Mark Davies – UK – Session 2 – Paper 0376

  15. Practical Example – New Residential Development Transfer Potential (% of HV EPR) 1 Mark Davies – UK – Session 2 – Paper 0376

  16. Practical Example – New Residential Development Transfer Potential (% of HV EPR) 1 2 Mark Davies – UK – Session 2 – Paper 0376

  17. Practical Example – New Residential Development Transfer Potential (% of HV EPR) 1 2 3 Mark Davies – UK – Session 2 – Paper 0376

  18. Effect of Soil Resistivity & Structure 3m 1m 300Ωm 1000Ωm 300Ωm 100Ωm Mark Davies – UK – Session 2 – Paper 0376

  19. Conclusions • A new calculation method is described which: • More accurately approximates transfer potential between HV and LV earthing systems in distributed LV networks (e.g. PME in the UK). • Accounts for the beneficial reduction in LV transfer potential provided by larger LV electrodes which are located further away from the HV substation (as previously demonstrated by measurement). • Is in good agreement with results from detailed simulation software (uniform soil). • The work is currently being used to develop new guidance / calculation tools for UK standards. • LV earthing design practice should be reviewed. The work suggests that LV electrode should be installed in parts of the network furthest from the HV electrode, e.g. at the end of LV feeder cables. • Work is progressing to evaluate the new calculation method with different arrangements, soil resistivity, etc. Mark Davies – UK – Session 2 – Paper 0376

  20. Application • During the design of MV distribution substations, LV electrodes should be biased towards the areas of the network furthest away from the HV electrode. • In existing networks where there is an unacceptably high transfer voltage on the LV earthing system. Additional LV electrode would be installed at strategic locations in areas remote from the HV electrode. • The approach could be extended to EHV Substations and the transfer potentials which may exist onto other adjacent HV electrodes or telecommunication circuits. Mark Davies – UK – Session 2 – Paper 0376

  21. New Design Methods to Achieve Greater Safety in Low Voltage Systems During a High Voltage Earth Fault Mark Davies Trevor Charlton Denis Baudin Mark Davies – UK – Session 2 – Paper 0376

More Related