eds 02-0031

Document Number: EDS 02-0031

Version: 4.0

Date: 21/11/2013

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ENGINEERING DESIGN STANDARD

EDS 02-0031

INSTALLATION OF POWER CABLES AND JOINTS IN AIR

Network(s): EPN, LPN, SPN

Summary: This standard describes the decision making process, methods and materials to be used when cables and joints are required to be installed in air and need to be protected from fire.

Originator: Paul Williams Date: 21/11/2013

Approved By: Steve Mockford Approved Date: 28/11/2013

Review Date: 28/11/2016

This document forms part of the Company’s Integrated Business System and its requirements are mandatory throughout UK Power Networks. Departure from these requirements may only be taken with the written approval of UK Power Networks’ Director of Asset Management. If you have any queries about this document please contact the originator of the current issue.

Document History

(The document history notes below are intended as a guide only and may not cover all of the changes. If you wish to make use of this document it should be read in full.)

Version Date Details Originator

4.0 21/11/2013 Document scope changed to cover all voltages Paul Williams

3.0 12/06/2012 Document reviewed and updated Paul Williams

2.2 22/08/2011 Document reclassified from EI to EDS Don Fossett

2.1 14/02/2011 Document rebranded Don Fossett

2.0 23/06/2009 Document reviewed and updated Paul Williams

1.0 13/01/2006 Original Issue Paul Williams

Installation of Power Cables and Joints in Air Document Number: EDS 02-0031

Version: 4.0

Date: 21/11/2013

© UK Power Networks 2013 All rights reserved 2 of 8

Contents

1 Introduction ............................................................................................................. 3

2 Scope ....................................................................................................................... 3

3 Design Guidelines Flow Chart for Installing Cable and Joints in Air ................... 4

4 Cable Installation ..................................................................................................... 5

4.1 New Cable Installations in Air .................................................................................... 5

Cable Types .............................................................................................................. 5 4.1.1

Cable Spacings ......................................................................................................... 5 4.1.2

4.2 Existing Cable Installations ........................................................................................ 5

5 Cable Joint Installation ........................................................................................... 6

5.1 Transition Joints between Existing Solid PILC and new XLPE Cables ....................... 6

Heatshrink Joints ....................................................................................................... 6 5.1.1

Resin Filled Joints ..................................................................................................... 6 5.1.2

Other Types of Resin Filled Joint ............................................................................... 7 5.1.3

5.2 XLPE to XLPE Joints ................................................................................................. 7

Heatshrink Joints ....................................................................................................... 7 5.2.1

Resin Filled Joints ..................................................................................................... 7 5.2.2

Other Types of Resin Filled Joint ............................................................................... 7 5.2.3

5.3 Transition Joints between Existing Fluid Filled and new XLPE Cables ...................... 8

5.4 Joint Spacings ........................................................................................................... 8

5.5 Existing Joint Installations.......................................................................................... 8


Version: 4.0

Date: 21/11/2013


1 Introduction

The purpose of this engineering design standard is to provide additional detailed guidelines for the actions to be taken when considering, installing and commissioning the installation of underground cables and cable joints in an in-air situation (i.e. cable tunnels, substations, cable basements, underground pits, etc.)

2 Scope

Underground cables and cable joints are designed to be buried direct in the ground. Installation in air should be avoided to limit the possible effects of a fire, caused by a failure and its subsequent spread, unless no other engineering solution is possible.

However, it is accepted that operational constraints mean that cables and joints do occasionally need to be installed in air.

This standard details the design guidelines, additional measures to be taken and materials to be used, when cables and joints have to be installed in an in-air situation.

The flow chart in Section 3 illustrates the decision process that shall be undertaken when deciding on the appropriate course of action to be employed when a project needs to consider the requirements for cable and joints to be installed in air.


Version: 4.0

Date: 21/11/2013


3 Design Guidelines Flow Chart for Installing Cable and Joints in Air

START

Does the project require

only cables to be installed

in air

No

Do the new cables have a

flame retardant sheath

Yes

No

Install cables as

required

Paint all exposed

cables with

intumescant paint

Yes

Can the joint be installed

with at least the minimum

spacing's in Section 4

Can the joint be located

in an area away from regular

personnel access

No

Yes

Do not install joint

seek alternative

location

Does the project

require cable & joints to be

permanently installed

in air

Yes

No

Is an approved

flame retardent joint

shell available

Yes

Can the joint

be located in a

suitatbly sized

bunded area

Do not install joint

replace cable from

end to end

Is the Joint a

Heatshrink

Joint

Paint exposed joint

and adjacent cables

with intumescant

paint

Is the Joint a resin

filled Joints

Yes

Yes

Use flame retardent

joint shell and fill

with approved resin

Yes

Is the Joint a fluid filled

Cable or fluid filled to XLPE

transition joint

No

No

Yes

Paint exposed joint

and adjacent cables

with intumescant

paint

Yes

Are the joints going

to be in service for less

than two years

No No

No

Yes

No


Version: 4.0

Date: 21/11/2013


4 Cable Installation

4.1 New Cable Installations in Air

Cable Types 4.1.1

All new install underground cables should have a flame retardant sheath, if they are to be installed in an in-air situation (i.e. in a cable tunnel, substation, cable basement or a cable pit), except where the exposed length is less than 3 metres when standard cables with either PVC or polyethylene sheaths can be used.

If a cable type without a flame retardant sheath needs to be installed, because the installation of a flame retardant cable is not practical or possible (i.e. there is no suitable position for a joint between the two cables types). Any exposed length of cable in excess of 3 metres shall be protected by a suitable intumescant paint, applied in accordance with the manufacturer’s instructions.

Tests have shown that three coats of Dulux Pyroshield Emulsion are sufficient to provide the required level of flame resistance for all types of cable.

Cable Spacings 4.1.2

Based on the information contained within the BEWAG* report – ‘Special report on Fire Resistant Cable Installation in Tunnels’, all new cross linked polyethylene (XLPE) low smoke zero halogen (LSOH) cables shall be installed in trefoil formation. *BEWAG – Berlin Power Utility, now part of the Vattenfall Europe Group.

In order to limit damage should a cable failure occur and to provide clear access, the minimum separation distances in Table 1 shall be observed:

Type of Spacing Minimum Separation Distance

Vertical separation between circuits 200mm

Horizontal clearance for personnel access Minimum 600mm

Cable and nearest adjacent floor or wall 200mm

Table 1 – Minimum Cable Spacings

In addition, consideration should be given to providing additional separation between adjacent critical circuits.

The provision of blast shielding between phases or circuits is not recommended as it is considered that it may increase the overall effects of a cable failure by not allowing the blast pressure to dissipate and create a pressure cell and increasing the likelihood of the blast being reflected back onto the fault area compounding the damage.

4.2 Existing Cable Installations

In these cases, where cables without a flame retardant sheath have already been installed in an in-air situation, the normal risk assessment process shall be carried out. If it is decided that additional precautions are required, the circuit(s) in question shall be switched out and the methods detailed in Section 4.1 of document shall be employed.


Version: 4.0

Date: 21/11/2013


5 Cable Joint Installation

In general, the installation of permanent cable joints in an in-air situation should be avoided unless no other economic engineering solution is possible, especially as experience shows that cable joints are more prone to in service failure.

Joints to be in service for a period of less than two years can be installed but are subject to the same installation requirements.

There are three main types of cable joints and each should be considered based upon the known reliability of each type:

5.1 Transition Joints between Existing Solid PILC and new XLPE Cables

Experience has shown that this particular type of joint is more prone to an electrical failure than other types due to a mix of old and new technology and particularly the condition of the existing PILC cables. Therefore, the use of such joints in an in-air situation should be avoided unless no other economic engineering solution is achievable.

Heatshrink Joints 5.1.1

When a standard commonly used heatshrink joint is to be used in an in-air environment. The surface of the each complete joint shall be painted with three coats of intumescant paint, applied in accordance with the manufacturer’s instructions.

Tests have shown that three coats of Dulux Pyroshield Emulsion are sufficient to provide the required level of flame resistance for all types of joint.

Resin Filled Joints 5.1.2

When a standard commonly used resin-filled joint is to be used in an in-air environment, the black plastic joint shell, supplied in the kit shall be replaced with a new clear plastic flame-retardant shell. Table 2 details the current available range of 11kV flame retardant joints shells available from UK Power Networks Logistics or the manufacturer TE Connectivity, currently these are only shells available at all voltages between LV and 132kV.

Joint Description 11kV Joint kit Stores Code

Flame Retardant Joint Shell Stores Code

Resin Volume

95 to 185mm Transition Straight Joint (Triplex to PILC) 04120S 04118M 13.0 Litres

240 to 300mm Transition Straight Joint (Triplex to PILC) 04121C 04119W 13.0 Litres

Table 2 – Flame Retardant Joint Shells for 11kV Transition joints

Each flame retardant joint shell is installed in the same manner as the existing shells supplied in each of the above kits, using the components in the kits and filled with the same volume of jointing resin.


Version: 4.0

Date: 21/11/2013


Other Types of Resin Filled Joint 5.1.3

For all other types of joint the surface of each complete joint shall be painted with three coats of intumescant paint, applied in accordance with the manufacturer’s instructions.


5.2 XLPE to XLPE Joints

Experience has shown that this particular type of joint is less prone to an electrical failure than other types. Therefore, the use of such joints in an in-air situation is acceptable as long as the following engineering solutions are applied.

Heatshrink Joints 5.2.1

When a standard commonly used heatshrink joint is to be used in an in-air environment. The surface of the each complete joint shall be painted with three coats of intumescant paint, applied in accordance with the manufacturer’s instructions.


Resin Filled Joints 5.2.2

When a standard commonly used resin-filled joint is to be used in an in-air environment, the black plastic joint shell, supplied in the kit shall be replaced with a new clear plastic flame-retardant shell. Table 3 details the current available range of 11kV flame retardant joints shells available from UK Power Networks Logistics or the manufacturer TE Connectivity, currently these are only shells available at all voltages between LV and 132kV.

Joint Description 11kV Joint kit Stores Code

Flame Retardant Joint Shell Stores Code

Resin Volume

35 to 95mm Triplex Straight Joint 04102U 04099J 6.0 Litres

150 to 300mm Triplex Straight Joint 04103E 04099J 6.0 Litres

Table 3 – Flame retardant joint shells for 11kV Transition joints

Each flame retardant joint shell is installed in the same manner as the existing shells supplied in each of the above kits, using the components in the kits and filled with the same volume of jointing resin.

Other Types of Resin Filled Joint 5.2.3

For all other types of new joint the surface of each complete joint shall be painted with three coats of intumescant paint, applied in accordance with the manufacturer’s instructions.



Version: 4.0

Date: 21/11/2013


5.3 Transition Joints between Existing Fluid Filled and new XLPE Cables

Experience has shown that this particular type of joint is less prone to an electrical failure than other types and as the pressure within the joint is continuously monitored the chance of failure is lower. Therefore, the use of such joints in an in-air situation is acceptable as long as the following engineering solutions are applied.

All joints of this type contain large volumes of potentially flammable cable fluid; therefore any joints of this type shall be installed in a suitably sized bunded area, large enough to capture the volume of oil contained in the joint and the fluid filled cable connected to it.

To prevent the spread of fire the surface of the each complete joint shall be painted with three coats of intumescant paint, applied in accordance with the manufacturer’s instructions.


5.4 Joint Spacings

In order to limit damage should a joint failure occur and to provide clear access, the minimum separation distances in Table 4 shall be observed:

Type of Spacing Minimum Separation Distance

Vertical separation between adjacent joints 200mm

Horizontal clearance between adjacent joints Minimum 600mm

Horizontal clearance for personnel access Minimum 600mm

Joint and nearest adjacent floor or wall 200mm

Table 4 – Minimum Cable Spacings

The provision of blast shielding between phases or circuits is not recommended as it is considered that it will increase the overall effects of a joint failure by not allowing the blast pressure to dissipate and create a pressure cell and increasing the likelihood of the blast being reflected back onto the fault area compounding the damage.

5.5 Existing Joint Installations

In these cases, where joints have already been installed in an in-air situation, the normal risk assessment process shall be carried out. If it is decided that additional precautions are required, the circuit(s) in question shall be switched out and the methods detailed in Sections 4.1 and 4.2 of this document shall be employed.

eds 02-0031

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