Transcript UK BP/SE/NSI 24

UK BP/SE/NSI 24
Colin Hepton
Keadby 400kV Substation
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.
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.
Dangers
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.
1.
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

Approaching and Working (1)

No restriction when approaching intact Earth
Systems.
 For Inadequate Earth Systems:
 Concrete Structures
 >10m where there is risk of system fault
 >1m where there is no risk of system fault
 In an emergency <10m is permissible, but >1m
must be upheld.
Approaching and Working (2)

For Inadequate Earth Systems
 Metallic Structures
 <1m approach is prohibited
 Same for Surge Arrestors and Cable Sealing
Ends (where they are independently earthed)
 Buried Earth Tape
 <1m SAP must perform a RA and identify
precautions to avoid Danger
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.
Limitations

NSI 24 not suitable for:
 Attachment to copper braided/multistranded
conductors.
 Repair/connection/disconnection to tape
between substation and terminal towers
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 <1m 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 t>2
months.
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.
Testing

Testing of Earth Systems should be made in
accordance with a Method Statement and RA.
 Flowchart for use when making RA.
THAT’S ALL FOLKS!