v6.0
Identification of High Voltage Cables
OwnerName / Peter Vujanic
Title / Head of Health, Safety, and Environment
Signature
Date / 01 May 2016
Authoriser
Name / Dudley Sparks
Title / Operational Safety Manager
Signature
Date / 01 May 2016
This document forms part of the UK Power Networks Integrated Management System and compliance with its requirements is mandatory. Departure from these requirements may only be taken with the written approval of the above authoriser.
Revision RecordVersion number / 6.0 / What has changed?
Document Owner name changed.DSR 01 015 Identification of Points of Work added.
Why has it Changed?
Change of structure.
New procedure
Date published / 01/05/2016
Next review date / 01/05/2019
Prepared by / R Hembling
Version number / 5.0 / What has changed?
Section 8.7 additional use of cable identifier in some circumstances when tracing from a cable end box.
And additional example added to reasons not to spike.
Section 8.10 wording added to allow a second SAP to confirm that spiking is the only option remaining
Section 8.11 wording change for clarity.
Section 8.13 I The word suspended removed
Why has it changed?
Variations to working practices
Feedback from Field operatives.
Actions from Incidents
Date published / 18/03/2015
Next review date / 27/01/2018
Prepared by / R Hembling
Version number / 4.1 / What has changed?
Two sentences added to section 8.4 regarding the use of mobile phones whilst identifying a cable using signal injection.
Why has it changed?
Field use Feedback
Date published / 15/05/2012
Next review date / 27/01/2015
Prepared by / N Saunders
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Contract Manager/Users
Contents
1.0Introduction and Purpose
2.0Scope
3.0Objective
4.0References
5.0Definitions
6.0Responsibilities
7.0Records
8.0Process Detail
9.0Superseded Documents
10.0Appendix A Identification of Cables by Signal Injection
11.0Appendix B Spiking Information
1.0Introduction and Purpose
This document gives the Approved procedure for identifying HVcables, the Approvedspiking procedure and other Approved means, which are required to comply with
DSR 5.9.2.
This document gives the approved procedure for moving a previously identified point of work, to another position on the same cable (or circuit).
2.0Scope
All operations in UK Power Networks Licence areas and on private networks that are owned or managed by UK Power Networks.
If any field operative requires to use any other means, then the field operative must obtain the consent of the DesignatedEngineer.
3.0Objective
To prevent injury to any person who is to work on a High Voltage (HV) cable.
To prevent damage being caused to the network Plant and Apparatus.
To prevent the inadvertent interruption of electricity supply to customers
4.0References
DSR / Distribution Safety Rules (Principally Rule 5.9.2)DSR 01 018 / Identification of LV cables
DSR 01 014 / Excavating near electricity cables
DSR 01 015 / Identification of Points of Work
HSS 40 029 / Unidentified cables
Approved Instrument List
HSS01 139 / Maintenance of spiking guns and cartridge storage
GTRA JHV02 / HV Jointing (including cable identification, stripping and preparation)
GTRA GOP22 / Identification of point of work and issuing of safety documents
GTRA EHV10 / EHV Jointing (including cable identification, stripping and preparation)
5.0Definitions
Spiking / The use of a cartridge operated spiking gun, or other approved device, which causes severe damage to the cable.A conventional cartridge operated spiking gun causes a metal chisel to penetrate the cable, to cause the damage. The method in which the spiking gun is used will depend on the type of cable being spiked.
Hydraulic cutters are not to be used instead of a spiking gun.
Possible consequences of spiking an incorrectly identified cable are given in appendix B.
6.0Responsibilities
It is the responsibility of all UK Power Networks employees and contractors working for UK Power Networks, to comply with the requirements of this procedure.
In particular, it is the responsibility of the Senior Authorised Person (SAP) in charge of the work, to correctly identify the HV cable and prove it Dead.
7.0Records
There are no specific records.
8.0Process Detail
8.1General Requirements
Before any work is undertaken on a High Voltage (HV) underground cable that is a part of the distribution network, then it shall first be made Dead, Isolated and Earthed in accordance with the Distribution Safety Rules, identified at the point of work by an approved method and proved Dead by approved means.
Where the work is to be carried out externally to the metallic Earth sheath (e.g. cathodic protection bonds, insulating sheath repairs etc.), confirmatory spiking is not required. However, it is essential that a Permit-to-Work (PTW) is issued by the Senior Authorised Person. The points of Isolation and Earthing shall be recorded on the document and Danger Notices posted on adjacent Live equipment.
8.2 Cable Records
Cable records give an indication of cable routes, type of construction and voltage. They give no reliable indication of depth, as ground levels may have altered over the years, or a cable’s position may have been changed by a third party without consent and not recorded. They should be seen as providing a guide, rather than a detailed location plan for a specific cable. Records should be used as a first step to locating and identifying a cable.
Cables may be encountered that cannot be identified by reference to cable records. These may be private or abandoned cables that have not been recorded. In these circumstances, the unidentified cable procedure HSS 40 029 should be followed.
8.3Excavation of Joint Holes
Where there are other cables near to the cable to be identified, then any nearby relevant cables (cables that cannot be reliably eliminated) must also be exposed. Signal injection (see 8.4) may be used to identify the cable, in which case a comparison of the signal strength on each cable and whether the signal strength varies as the detector is moved around, or along the cables, will help to determine which cable has been injected with the signal. Particular care is required when using a detector around rather than along a cable. This is because any variations in signal strength may be due to changes in distance from a nearby cable rather than due to the internal twisting of the cores of the cable.
If in doubt, seek advice from a SAP.
8.4Identification by Signal Injection
Signal Injection is the preferred method of cable identification. The cable shall be isolated and earthed in accordance with DSR 4.1.1. A Sanction-for-Test (SFT) must then be issued.
The signal injection instrument (see approved instrument list) has two leads which must be connected between two cores of the cable. This connection is made by the use of test plugs, or integral test connections on switchgear (if available), or to an accessible cable termination such as an overhead line, or cable sealing ends.
The person connecting the instrument must ensure that the connection points have been effectively earthed to discharge all stored electrical charge, before they are approached or touched.
The person conducting the test must consider if a second person is required during the testing. This second person must be competent to avoid danger and must also understand what is being done.
It is essential that the instrument leads are connected between two phase cores, so that the signal does not find alternative earth paths and so reduce the possibility of an unwanted signal on another cable.
The remote end of the cable will usually be in the earthed position. The earth will provide a short circuit path between all phases.
On teed or multi-branch circuits, it may be necessary to remove and apply earths appropriately, so as to be able to identify the correct Branch of the cable (see appendix A).
At the point of work, the signal shall be picked up by the use of a detector. If the detector is moved around, or along, a conventional cable, the signal strength will vary due to the internal twisting of the cores. This variation in signal strength will demonstrate that the signal is in the cores and not in the earth sheath of the cable.
When possible, it is preferable to move the detector along the length of the cable, rather than just around the circumference of the cable. Experience has shown that this normally gives a better result, as the detector traverses a greater distance.
If the signal strength is constant, as the detector is moved around or along the cable, then the cable may not be the correct one. Further tests and investigation will then be required.
If the cable is accessible at a location other than the joint hole, and its identity is known then an instrument that induces a signal into the sheath of the cable may be used. The signal is induced usually into the sheath of the cable by using a Current Transformer and a signal detector is used to detect the signal at the point of work (see also 8.12).
The detector shall be used to listen for the presence or absence, of a signal on all the exposed cables.
Be aware that a signal may be induced from mobile telephones into the listening device. Switch OFF all mobile telephones when using this type of equipment.
Operatives using the signal equipment shall ensure that they are familiar with the equipment and know how to use it correctly.
Following the identification of the cable by signal injection, the cable shall normally be spiked (see 8.6).
8.5Identification of Single Core Cable Circuits
The introduction of polymeric insulation has led to the wide spread use of single core cables. These are mostly used in groups of three to form a circuit, instead of using a composite three core cable.
Additional care is required when identifying circuits comprising of three single core cables, when there are other nearby circuits which also comprise single core cables. There is some possibility that the cores may have incorrectly been placed in groups of three, thereby meaning that the group of three single core cables may not belong to the same circuit. Even if the single core cables are in a duct, or have been tied together, the possibility may still exist that they do not belong to the same circuit.
By attaching the signal injector leads to two phases, it is usually possible to determine which two of the three single core polymeric cables have the strongest signal. By disconnecting the signal injector lead from one of the phases and connecting it onto the phase that was not previously injected, it will usually be possible to then identify the third single core cable which previously did not have a signal. If the signal is weak or non-existent in any of the three single core cables, it is possible that the cables have been incorrectly grouped. Further tests and investigation will then need to be made.
8.6Exceptions to Spiking a Cable
Exceptions to spiking a cable are restricted to the following work (and those detailed in the following sections of this procedure):
Work on pressurised primary system cables that does not involve disturbing the main insulation of the cable, for example:
a)sheath repairs;
b)temporary leak repairs;
c)repairs to apple wipes and band wipes;
d)removal of a fibre glass joint box or heat shrink sleeve for joint inspection;
e)freezing;
f)application of epoxy resin sheath reinforcement;
g)serving repairs on insulated sheath cables
h)removal of a ring of sheath to inspect and repair minor surface impact damage on pressurised cables, where it is considered that a sleeve repair can be carried out ;
(II)The complete break down and remake of a primary system pressurised joint to carry out repair work.
(III)Exception to spiking primary system polymeric and paper solid cables is restricted to the following work only:
- topping up oil filled reservoir joints on paper cables.
- serving repairs.
Where the work to be carried out is of the type described in this section and in the opinion of the SAP it is safe not to spike, it will not be necessary to do so, provided the procedures detailed below are complied with.
At the point of work the SAP will explain to the person who will receive the PTW how the cable has been made dead and where it has been earthed. The SAP will then show that the cable can be identified by reference to records. This will include reviewing any available circuit history accompanying the records, with particular attention being paid to any historic work on a circuit and the impact this work might have had on the cable layout or joint designations at the point of work.
The SAP will inject a signal into the cable and will listen at the point of work as required by section 8.4. In addition where there are adjacent live circuits the listener should also be used to confirm the absence of mains hum in the identified cable when compared with the live cables.
Where (ii) above gives a very positive result, but is at variance with the records and this cannot be explained then, where reasonably practicable, adjacent live cables should be made dead. If this is not reasonably practicable and it is still considered safe not to spike then a second SAP familiar with cable work will be required to visit site and satisfy themselves that all precautions have been taken. The second SAP will confirm that they agree that it is not necessary to spike the cable, and this will be written on the PTW. The second SAP will endorse the issue of the PTW by signing alongside the person issuing the PTW. This will be recorded with Control. Work on the cable will be started under the personalsupervision of both SAPs.
In any case where (i) and (ii) above give ambiguous results or cannot be complied with, or it is considered unsafe to proceed without spiking, with the adjacent cables, then the adjacent cables must be made dead, or the cable must be spiked.
8.7Identification by cable tracing
It may be reasonably possible to trace a cable from a known Earthed position, such as:
- A switchgear cable end box: Care is required due to the different layout of cable boxes on switchgear especially that controlling Transformers and where reasonably practicable the identification shall be confirmed by using signal injection.
- A cable sealing end
- An overhead line
The cable must be positively traced along its entire route from the known earthed position to the point of work. A noose of non-conductive material shallbe run from the known Earthed termination, to the point of work. If it is not possible to use a running noose, then another approvedmethod must be used (e.g. signal injection).
When identifying a cable by cable tracing and the cable passes through a hole in a wall, it is mandatory to run the noose through the hole. Tapping or tugging the cable, using rods, or any other unapproved techniques are prohibited.
Where a cable passes through a duct line, it is prohibited to rod the duct as a method of identification. There have been instances where this technique has failed in the past, when the rod has passed from one duct line into another, so giving incorrect cable identification.
A cable that is identified at the point of work by positive tracing shall normally be spiked. However, where the cable has been identified by positive tracing and the SAP has good grounds not to spike the cable, then the cable need not be spiked.
Three typical examples of good grounds are:
- A physical restriction or difficulty preventing the application of the spiking gun.
- That the spiking of the cable would result in the need to extend the cable, so producing additional work.
- Where the earth connection is clearly visible and the cable has been physically traced from that earth.
8.8Transformer Feeder Identification, by Signal Injection Method (HV/LV)
Where HV test access is not available, to simplify the procedure and avoid the necessity for removing the lid of the distribution transformer, the test signal may be injected into the LV winding, with an earth applied at the source end of the HV cable (see appendix A). Due to the turns ratio of the transformer windings, the signal current produced in the HV cable will be smaller than with direct injection but it is still normally adequate for identification purposes.
A phase to phase connection for signal injection into the LV winding is preferable, although a comparable signal level can be obtained by connecting between phase and neutral. (The primary and secondary windings of the transformer are linked solely by electromagnetic coupling and the presence of a single earth connection on each voltage system i.e. HV cable earth and LV neutral earth connection, will not cause signal current to flow in the cable sheath or via earth return paths).