UK BP/SE/NSI 24

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UK BP/SE/NSI 24

• Colin Hepton
• Keadby 400kV Substation

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Scope

• Approaching and Working on Earth Systems (and
  associated conductive parts).
• Incorporates TGN(T) 114 - Replacement of stolen
  Earth Tape.
• Additional Procedures for work on Railway
  Operator Connections.

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Definitions

• Earth Bond - Bonds for purpose of providing Earth
  Continuity on Earth Connections.
• Approved Earth Bond and Pole - Detailed in TGN(T)
  114 and are used to make/break connections in
  Main Earth Systems. Not rated for System Fault.
• Main Earth System - Arrangement of interconnected
  buried or surface conductors providing an
  electrical connection to True Earth, which are
  intended to carry HV fault current.
• Other Earth System - Earth Conductors which are
  part of the system but which are not part of the
  Main Earth System.
• Intact System - Any Earth System in which there
  are no breaks in the Earth Conductors.
• Inadequate System - Any Earth System in which
  there are breaks in the Earth Conductors.
• Poor Weather Conditions - Lightning, Snow Storms,
  Heavy or persistent rain, fog or mist.

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Dangers

1. Differences in Potential (including Step, Touch
   and Transferred - steady and fault) across the
   Earth System in which parts are incomplete,
   segregated or without continuity.
2. Flying Debris due to faults on equipment that is
   inadequately Earthed.
3. Rise of Earth Potential from Earth Faults on
   adjacent systems currents which flow in Earth
   Systems.

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General Principles to avoid Danger.

• Any part of the Earth System must be considered
  to be an Electrical Conductor
• Work must be carried out by a Competent Person
  under an appropriate Safety Document
• Disconnect associated equipment from sources of
  electrical energy which could give rise to danger
• Bonding across before making or breaking any
  Earth System connections
• Insulated Working
• Ensure that remote earths are not introduced
  which could be at a different potential to local
  earth

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Approaching and Working (1)

• No restriction when approaching intact Earth
  Systems.
• For Inadequate Earth Systems
• Concrete Structures
• gt10m where there is risk of system fault
• gt1m where there is no risk of system fault
• In an emergency lt10m is permissible, but gt1m must
  be upheld.

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Approaching and Working (2)

• For Inadequate Earth Systems
• Metallic Structures
• lt1m approach is prohibited
• Same for Surge Arrestors and Cable Sealing Ends
  (where they are independently earthed)
• Buried Earth Tape
• lt1m SAP must perform a RA and identify
  precautions to avoid Danger

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Approaching and Working (3)

• Working on Main Earth Systems
• Make/Break connections can only be made after
  they have been bridged using a connection of
  equivalent current carrying capacity, unless RA
  indicates no significant hazard
• Other Earth Systems
• Requirement for RA applies, any Earth Bond must
  be appropriate for duty.

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Limitations

• NSI 24 not suitable for
• Attachment to copper braided/multistranded
  conductors.
• Repair/connection/disconnection to tape between
  substation and terminal towers

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Application of Earth Bonds to Main Earth Systems

• Application/Removal should not occur where there
  is an increased risk of a System fault.
• Only Approved Earth Bonds and Poles should be
  used.
• One end should be connected to an intact Earth
  System. Approach lt1m can be made to do this, but
  the Earth Bond should be between person and
  connection point.
• Earth Bonds should not be relied upon for tgt2
  months.

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Application of Earth Bonds to Other Earth Systems

• RA and control measures identify the Earth Bond
  to be used and its application.
• Order of application and removal should also be
  made clear.

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Testing

• Testing of Earth Systems should be made in
  accordance with a Method Statement and RA.
• Flowchart for use when making RA.

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THATS ALL FOLKS!