National Grid Acton Lane 22kV Substation – Operational Requirements

National Grid Acton Lane 22kV Substation – Operational Requirements

Contents

1Introduction

2Scope

3Abbreviations and Definitions

4Network Diagram

5Site Labelling and Network Diagram Annotation

6Operational Considerations

7Other Supplies

8References

1Introduction

National Grid Acton Lane 22kV (ACTL8)substation is supplied at LV from UK PowerNetworksActon Ln Opp Waxlow Rd National Grid (24843)11kV/400V substation which is also located within the National Grid site. Although Acton Lane 22kV is classified as a COLD site with an earth potential rise (EPR) of 330V (as of 01 November 2013) it is treated as HOT (with an EPR in excess of 650V) for the provision of LV supplies in accordance with EDS082108. This has implications on both the site earthing and the application of circuit main earths.

The earthing associated with the two ring main units (the second is currently unused) at Acton Ln Opp Waxlow Rd National Grid (24843) substation is non-standard.The HV cable screens on the incoming cables, outgoing cables and the cables between ring main units are connected together but are not connected to the National Grid substation earth.

If National Grid Acton Lane 22kV substation has an EPR in excess of 650V then Acton Ln Opp Waxlow Rd National Grid (24843) substation should not be used to apply a circuit main earth to other parts of the UK Power Networks distribution network as there is a risk of exporting the EPR to other secondary substations and onto other customer supplies.

A diagram of the relevant network is shown in Section 3.

2Scope

This document applies to the following UK Power Networks substations in London:

  • Gibbons Road (240).
  • Acton Ln Opp Waxlow Rd National Grid (24843).
  • Waxlow Rd Unit A Centrus (24731).

3Abbreviations and Definitions

Term / Definition
EPR / Earth potential rise – the potential (voltage) rise that occurs on any metalwork due to the current that flows through the ground when an earth fault occurs on the network
ROEP / Rise of earth potential – another term for EPR
HOT Site / A site where the EPR is greater than 430V or 650V (for high reliability protection with a fault clearance time less than 200ms)
COLD Site / A site where the EPR is less than 430Vor 650V (for high reliability protection with a fault clearance time less than 200ms)
Power On / UK Power Networks network management system

4Network Diagram

5Site Labelling and Network Diagram Annotation

5.1.1Warning Labels

Warning labels have been installed at the affected sites as shown in the diagram above to warn operational staff.

5.1.2Power On Annotation

A HOT Site pin hasalso been placed on the Power On diagram at affected sites.

6Operational Considerations

6.1Overview

Special care is needed in the positioning of circuit main earthsto:

  • Prevent the EPR beingexported to other substations and customers.
  • Reduce the risk to field operatives that can arise from simultaneous contact between different earthing systems.

The Distribution Safety Rules shall be followed at all times and insulated working should be considered where applicable. HSS 40 050 (Controlling Impressed Voltages on Underground Cable Systems) provides further guidance on the additional precautions that should be considered when working on unground cable systems and the application of insulated working. National Grid NSI 5 (Insulated Working on Cable Systems) also provides guidance on the insulated working practices.

Standard isolation and earthing arrangements may be used in the following situations:

  • Confirmation from National Grid that the earth potential rise (EPR) at National Grid Acton Lane 22kV substation does not exceed 650V. This information can be obtained from the National Grid Control Centre. Note: If the EPR under standard running arrangements is greater than 630V it may be possible for National Grid to change the running arrangements to reduce the EPR to an acceptable level.
  • The duration of the work is short[1] (i.e. less than one day) and does not involve making or breaking any earth or cable connections and it is also not considered reasonably practical to turn off the supply to National Grid Acton Lane 22kV substation.

However if the above conditions cannot be satisfied the locations/situationsdetailed in the following sectionsrequire particular attention.

6.2Maintenance or Replacement at Acton Ln Opp Waxlow Rd National Grid (24843)

Point of isolation and circuit main earths at:

  • Gibbons Road (240)Panel 48.
  • Waxlow Rd Unit A Centrus (24731).
  • Acton Ln Opp Waxlow Rd National Grid (24843) RMU1 CB (isolation only).
  • Acton Ln Opp Waxlow Rd National Grid (24843) RMU2 CB (isolation only).

Note:To work on the ring main units it may be necessary to apply an earth which may connect two different earthing systems together; therefore the duration of the applied earth should be kept to a minimum.

6.3Maintenance or Replacement at Waxlow Rd Unit A Centrus(24731)

Point of isolation and circuit main earths at:

  • Gibbons Road (240) Panel 48.
  • Acton Lne Hamm Med Res (24650).
  • Acton Ln Opp Waxlow Rd National Grid (24843) RMU1 CB (isolation only).
  • Acton Ln Opp Waxlow Rd National Grid (24843) RMU2 CB (isolation only).
  • Waxlow Rd Unit A Centrus(24731) CB (isolation only).
  • All other HV switches at Acton Ln Opp Waxlow Rd National Grid (24843)should be closed and locked off.

6.4Cable Repair or Replacement between Gibbons Road (240) and Acton Ln Opp Waxlow Rd National Grid (24843)

Point of isolation and circuit main earths at:

  • Gibbons Road (240)Panel 48.
  • Waxlow Rd Unit A Centrus (24731).
  • Acton Ln Opp Waxlow Rd National Grid (24843) RMU1 CB (isolation only).
  • Acton Ln Opp Waxlow Rd National Grid (24843) RMU2 CB (isolation only).
  • All other HV switches at Acton Ln Opp Waxlow Rd National Grid (24843)should be closed and locked off.

6.5Cable Repair or Replacement between Acton Ln Opp Waxlow Rd National Grid (24843) and Waxlow Rd Unit A Centrus(24731)

Point of isolation and circuit main earths at:

  • Gibbons Road (240) Panel 48.
  • Waxlow Rd Unit A Centrus (24731).
  • Acton Ln Opp Waxlow Rd National Grid (24843) RMU1 CB (isolation only).
  • Acton Ln Opp Waxlow Rd National Grid (24843) RMU2 CB (isolation only).
  • All other HV switches at Acton Ln Opp Waxlow Rd National Grid (24843)should be closed and locked off.

6.6Jointing and Cable Connection

All jointing work shall be carried out in accordance with National Grid NSI 5. Also all final connections between different earthing systems shall be made via cable joints and not direct connections onto the equipment.

7Other Supplies

The substation at Acton Ln Opp Waxlow Rd National Grid (24843) shall not be used to provide LV supplies to other customers.

8References

EDS060002 / HOT Site Requirements
EDS 08-2108 / Supplies to HOT Sites and National Grid Sites
HSS 40 050 / Controlling Impressed Voltages on Underground Cable Systems
National Grid NSI 5 / Insulated Working on Cable Systems

EDS 08-2108B Version 2.0

21/09/2017Page 1 of 5

[1] The likelihood of a fault occurring for short duration is minimal and therefore the risk of an EPR greater than 650V is also minimal.