ECS INSTALLATION OF POWER CABLES AND JOINTS IN AIR

Transcription

1 Document Number: ECS Network(s): Summary: ENGINEERING CONSTRUCTION STANDARD ECS INSTALLATION OF POWER CABLES AND JOINTS IN AIR EPN, LPN, SPN 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. Author: Jesse Garcia Approved By: Paul Williams Approved Date: 23/12/2016 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 the Director of Asset Management. If you have any queries about this document please contact the author or owner of the current issue. Applicable To UK Power Networks All UK Power Networks Asset Management Capital Programme Connections HSS&TT Network Operations UK Power Networks Services Other External G81 Website Contractors ICPs/IDNOs Meter Operators THIS IS AN UNCONTROLLED DOCUMENT, THE READER MUST CONFIRM ITS VALIDITY BEFORE USE

2 Revision Record Version 5.0 Review Date 23/12/2021 Date 21/11/2016 Author Jessie Garcia Reason for Change: Periodic review. What has changed: Document type changed to Engineering Construction Standard (from EDS ). Table 3 in section updated with new UK Power Networks Stores Codes. Version 4.0 Review Date 21/11/2016 Date 21/11/2013 Author Paul Williams Document scope changed to cover all voltages Version 3.0 Review Date Date 12/06/2012 Author Paul Williams Document reviewed and updated Version 2.2 Review Date Date 22/08/2011 Author Don Fossett Document reclassified from EI to EDS Version 2.1 Review Date Date 14/02/2011 Author Don Fossett Document rebranded Version 2.0 Review Date Date 23/06/2009 Author Paul Williams Document reviewed and updated Version 1.0 Review Date Date 13/01/2006 Author Paul Williams Original Issue UK Power Networks 2016 All rights reserved 2 of 9

3 Contents 1 Introduction Scope Design Guidelines Flow Chart for Installing Cable and Joints in Air Cable Installation New Cable Installations in Air Cable Types Cable Spacings Existing Cable Installations Cable Joint Installation Transition Joints between Existing Solid PILC and new XLPE Cables Heatshrink Joints Resin Filled Joints Other Types of Resin Filled Joint XLPE to XLPE Joints Heatshrink Joints Resin Filled Joints Other Types of Resin Filled Joint Transition Joints between Existing Fluid Filled and new XLPE Cables Joint Spacings Existing Joint Installations... 9 UK Power Networks 2016 All rights reserved 3 of 9

4 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.) 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. 2 Scope This standard applies to the installation of all cables and cable joints installed in air from LV to 132kV. UK Power Networks 2016 All rights reserved 4 of 9

5 3 Design Guidelines Flow Chart for Installing Cable and Joints in Air START Does the project require only cables to be installed in air Do the new cables have a flame retardant sheath Install cables as required Does the project require cable & joints to be permanently installed in air Paint all exposed cables with intumescant paint Are the joints going to be in service for less than two years Can the joint be located in an area away from regular personnel access Do not install joint seek alternative location Do not install joint replace cable from end to end Can the joint be installed with at least the minimum spacing's in Section 4 Is the Joint a Heatshrink Joint Paint exposed joint and adjacent cables with intumescant paint Is the Joint a resin filled Joints Is an approved flame retardent joint shell available Use flame retardent joint shell and fill with approved resin Is the Joint a fluid filled Cable or fluid filled to XLPE transition joint Can the joint be located in a suitatbly sized bunded area Paint exposed joint and adjacent cables with intumescant paint UK Power Networks 2016 All rights reserved 5 of 9

6 4 Cable Installation 4.1 New Cable Installations in Air Cable Types All new install underground cables shall 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 intumescent paint, applied in accordance with the manufacturer s instructions. required level of flame resistance for all types of cable Cable Spacings 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: Table 2.1 Minimum Cable Spacings Type of Spacing Vertical separation between circuits Horizontal clearance for personnel access Cable and nearest adjacent floor or wall Minimum Separation Distance 200mm Minimum 600mm 200mm 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. UK Power Networks 2016 All rights reserved 6 of 9

7 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 When a standard commonly used heatshrink joint is to be used in an in-air environment. The surface of each completed joint shall be painted with three coats of intumescent paint, applied in accordance with the manufacturer s instructions Resin Filled Joints 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 flameretardant 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. Table 5.1 Flame Retardant Joint Shells for 11kV Transition Joints 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 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. UK Power Networks 2016 All rights reserved 7 of 9

8 5.1.3 Other Types of Resin Filled Joint For all other types of joint the surface of each complete joint shall be painted with three coats of intumescent 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 When a standard commonly used heatshrink joint is to be used in an in-air environment. The surface of each complete joint shall be painted with three coats of intumescent paint, applied in accordance with the manufacturer s instructions Resin Filled Joints 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 flameretardant 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. Table 5.2 Flame Retardant Joint Shells for 11kV Triplex Straight Joints Joint Description 11kV Joint Kit Stores Code Flame Retardant Joint Shell Stores Code Resin Volume 35 to 95mm Triplex Straight Joint 04090V 04099J 8.0 Litres 150 to 185mm Triplex Straight Joint 04091F 04099J 8.0 Litres 240 to 130mm Triplex Straight Joint 04092Q 04099J 8.0 Litres 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 For all other types of new joint, the surface of each complete joint shall be painted with three coats of intumescent paint, applied in accordance with the manufacturer s instructions. UK Power Networks 2016 All rights reserved 8 of 9

9 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 each completed joint shall be painted with three coats of intumescent 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: Table 5.3 Minimum Cable Spacings Type of Spacing Vertical separation between adjacent joints Horizontal clearance between adjacent joints Horizontal clearance for personnel access Joint and nearest adjacent floor or wall Minimum Separation Distance 200mm Minimum 600mm Minimum 600mm 200mm 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 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. UK Power Networks 2016 All rights reserved 9 of 9