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Document Number: EMS 10-0602 Date: 12/09/2016 ENGINEERING MAINTENANCE STANDARD EMS 10-0602 EARTHING ASSESSMENT PROCESS Network(s): EPN, LPN, SPN Summary: This document details the process for carrying out earthing assessments as part of work detailed in maintenance standard EMS 10-0601. Author: Stephen Tucker Date: 12/09/2016 Approved By: Barry Hatton Approved Date: 06/10/2016 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 External All UK Power Networks G81 Website Asset Management Contractors Capital Programme ICPs/IDNOs Connections Meter Operators HSS&TT Network Operations UK Power Networks Services Other THIS IS AN UNCONTROLLED DOCUMENT, THE READER MUST CONFIRM ITS VALIDITY BEFORE USE Version: 1.0 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 Revision Record Version 1.0 Review Date 12/09/2017 Date 12/09/2016 Author Stephen Tucker New document to cover grid and primary substation assessment process and support the requirements of EMS 10-0601 Version Review Date Date Author Why has the document been updated: What has changed: © UK Power Networks 2016 All rights reserved 2 of 11 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 Contents 1 Introduction ................................................................................................................4 2 Scope ..........................................................................................................................4 3 Glossary and Abbreviations .....................................................................................4 4 Prerequisites ..............................................................................................................4 5 Process .......................................................................................................................5 5.1 Annual Programme ..................................................................................................... 5 5.2 Planning ...................................................................................................................... 5 5.3 Site Work ..................................................................................................................... 5 5.4 EPR Assessment ........................................................................................................ 6 5.5 Safety Voltage Assessment ........................................................................................ 6 5.6 Review ........................................................................................................................ 7 5.7 Re-design .................................................................................................................... 7 6 Reporting ....................................................................................................................7 7 Invoicing .....................................................................................................................8 8 Review Meetings ........................................................................................................8 9 Audits ..........................................................................................................................8 10 References ..................................................................................................................9 10.1 UK Power Networks Standards ................................................................................... 9 10.2 National Standards ...................................................................................................... 9 11 Dependent Documents ..............................................................................................9 Appendix A – Earthing Report and Drawing Naming Conventions ................................10 A.1 Filename ................................................................................................................... 10 A.2 PDF Properties .......................................................................................................... 11 A.3 Dates ......................................................................................................................... 11 Tables Table 5-1 – Typical Ground Return Current Percentages .......................................................6 Table 5-2 – Typical Fault Clearance Times .............................................................................6 Table A-1 – Filename Format ................................................................................................10 Table A-2 – PDF Properties ...................................................................................................11 Table A-3 – Date Format .......................................................................................................11 © UK Power Networks 2016 All rights reserved 3 of 11 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 1 Introduction This document details the process for carrying out earthing assessments at primary and grid substations as part of work detailed in maintenance standard EMS 10-0601. The highly technical nature of this work generally requires the services of a specialist earthing contractor/consultant to carry out the measurement, site survey, modelling and assessment activities to ensure safety voltage limits are acceptable and the substation can be classified as safe. 2 Scope This procedure applies to all primary and grid earthing survey and assessments carried in accordance with EMS 10-0601 in EPN, LPN and SPN. 3 Glossary and Abbreviations Term Definition Alfresco UK Power Networks document management system COLD Site A site where the EPR is less than or equal to 430V or 650V (for high reliability protection with a fault clearance time less than 200ms) EPR Earth potential rise – the potential (voltage) rise that occurs on any metalwork due to the current that flows through the ground when an earth fault occurs on the network HOT Site A site where the EPR is greater than 430V or 650V (for high reliability protection with a fault clearance time less than 200ms) NetMap UK Power Networks graphical information system (GIS) PowerOn UK Power Networks network management system (NMS) 4 Prerequisites The following are required to carry out the work detailed within this document: • • • • Suitable earthing measurement equipment. CDEGS (Current Distribution, Electromagnetic Fields, Grounding and Soil Structure Analysis) licence. UK Power Networks substation entry up to 132kV. Access to UK Power Networks IT systems including Earthing Database, NetMap, PowerOn, Alfresco PowerShare and Alfresco EnterpriseShare. © UK Power Networks 2016 All rights reserved 4 of 11 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 5 Process 5.1 Annual Programme J F M A M J J A S O N D Planning Site Work Assessments Reports Review Meetings 5.2 Planning Before the site visit: 1. Review existing earthing information including the earthing database, Alfresco PowerShare and any previous design and assessment reports. 2. Obtain substation earthing layout drawing and/or site layout from UK Power Networks. 3. Determine suitable measurement routes using geographical maps of the surrounding area and NetMap. 4. If required identify the landowner using the Land Registry web site and notify the landowner of the intent to carry out measurements. Notify UK Power Networks of any access problems. 5. Request any other required information from UK Power Networks or third parties e.g. National Grid. 6. Examine PowerOn system to identify any operational restrictions and plan accordingly. 5.3 Site Work 5.3.1 General All site work shall be carried out in accordance with HSS 40 xxx. 5.3.2 Measurements Review any existing earthing measurement records. Where required carry out soil resistivity measurements and/or a fall-of-potential earth resistance measurement as specified in EMS 10-0601 and ECS 06-0024. 5.3.3 Earthing Survey Carry out an earthing survey as detailed in EMS 10-0601 and record the results on form ECP 11-0406. © UK Power Networks 2016 All rights reserved 5 of 11 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 Create a drawing of the main parts of the existing earthing. Record and any defects found during the survey and note the different types of surface covering found in and around the substation. Provide a report (based on EMS 10-0601a format) containing the soil resistivity measurement results, measured earth resistance, a list of defects and continuity measurements. 5.4 EPR Assessment An assessment of the EPR shall be carried as follows: 1. Analyse the circuit data from NetMap to determine the supply details and the fault current data provided by UK Power Networks to determine the ground return current using the approach detailed in ENA ER S34. Ground return reductions to account for the current returning via the cable sheaths can be applied in accordance with Table 5-1. Table 5-1 – Typical Ground Return Current Percentages Voltage Ground Return Current (Igr) 132kV 34.5% 33kV 23.3% 11kV or 6.6kV 37.4% 2. Calculate the EPR from the measured earth resistance and the calculated ground return current. 3. Classify the site as HOT or COLD in accordance with ENA ER S36. 5.5 Safety Voltage Assessment An assessment of the safety voltages shall be carried out as follows: 1. Create a CDEGS computer model of the existing substation earth electrode from existing drawings and/or the findings of the survey (Section 5.3.3). 2. Carry out an assessment of the touch and step potentials using the approach in BS EN 50522 (a similar approach is being incorporated into the next revision of ENA TS 41-24). 3. Check the calculated touch and step potentials against the tolerable limits in ENA TS 41-24 using the typical fault clearance times detailed in Table 5-2. Table 5-2 – Typical Fault Clearance Times Voltage Fault Clearance Time 132kV 0.2s 33kV 0.5s 11kV or 6.6kV 1.0s 4. If unsafe check using BS EN 50522 tolerable limits. © UK Power Networks 2016 All rights reserved 6 of 11 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 5. If unsafe request site specific protection settings and check against ENA TS 41-24 and BS EN 50522 limits. 6. If unsafe request fault current data based on the measured site resistance. For 132kV substations request detailed fault current data, with vector format, per-phase current flows on each line and transformer, to allow neutral currents to be subtracted. 7. Review the measured earth resistance and check if correct. Calculate the value for a safe site using the existing surface type including any surrounding cable network and include in report. 8. If unsafe review with UK Power Networks and then produce an earth electrode redesign to address the issues. 9. Add a summary of the main findings to the report. 5.6 Review Review all reports at a bi-monthly meeting with UK Power Networks. 5.7 Re-design If the initial assessment of the touch and step potentials (Section 5.5) exceeds the tolerable limits carry out a substation re-design as outlined below: 1. Design an earth electrode system to accommodate any new plant, integrate with the existing earthing and bring the earthing of the substation in line with current UK Power Networks earthing standards (EDS 06-0013). 2. Provide the proposed earthing design in AutoCAD format drawn on an equipment layout drawing provided by UK Power Networks. 3. Add the proposed earth electrode to the CDEGS model. 4. Calculate touch and step potentials across the proposed arrangement for the fault clearance times provided. If necessary, make refinements to the design to ensure that touch and step potentials are within ENA TS 41-24 tolerable limits. 5. Produce contour plots showing the touch and step potentials across the site for the proposed earthing arrangement. Plot the HOT zone, if applicable, based on an outline model of the substation cable network. 6. Add a summary of the main findings and the above plots to the report. 6 Reporting All completed test forms and reports shall be provided in pdf format. All drawings shall be provided in MicroStation or AutoCAD and pdf format. All reports and drawings shall use the filename and pdf property naming convention specified in Appendix A. © UK Power Networks 2016 All rights reserved 7 of 11 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 7 Invoicing Each activity shall be listed as a separate invoice item based on the agreed contractual rates. Invoicing shall be tracked on a spreadsheet in a format agreed with UK Power Networks. This will include the activities undertaken at each substation, the invoice amount and a total for each operational area and comparison to the purchase order total. 8 Review Meetings Regular review meetings shall take place, e.g. every two months and will normally involve the following attendees: • • • • UK Power Networks’ project manager. UK Power Networks’ health and safety representative. UK Power Networks’ procurement representative. Contractor project manager. A typical agenda for the review meeting is as follows: • • • • • • • • • • 9 Introductions and housekeeping. Safety message. Review actions. KPIs. Health and safety. Audit findings. Progress review. Invoicing. AOB. Date of next meeting. Audits UK Power Networks shall carry out a regular audit of the site assessment team to ensure the procedure outlined in HSS 40 057 is being followed. The contractor is also responsible for undertaking audits of their own staff. Any issues raised during the audits shall be reported at the review meetings and resulting actions captured as part of the meeting actions with responsibility apportioned. © UK Power Networks 2016 All rights reserved 8 of 11 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 10 References 10.1 UK Power Networks Standards EDS 06-0013 Grid and Primary Substation Earthing Design ECS 06-0022 Grid and Primary Substation Earthing Construction ECS 06-0024 Earthing Testing and Measurements EMS 10-0601 Earthing Inspection, Assessment and Maintenance EMS 10-0601a EPR Assessment Report ECP 11-0406 Earthing System Test Form HSS 40 057 Substation Earthing Assessment 10.2 National Standards ENA TS 41-24 1 Guidelines for the Design, Installation, Testing and Maintenance of Main Earthing Systems in Substations ENA ER S341 A Guide for Assessing the Rise of Earth Potential at Substation Sites 1 ENA ER S36 Procedure to Identify and Record HOT Substations BS EN 50522 Earthing of Power Installations Exceeding 1kV AC 11 Dependent Documents The documents below are dependent on the content of this document and may be affected by any changes. EMS 10-0601 1 Earthing Inspection, Assessment and Maintenance Available from www.energynetworks.org. © UK Power Networks 2016 All rights reserved 9 of 11 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 Appendix A – Earthing Report and Drawing Naming Conventions A.1 Filename All earthing reports and drawings shall use relevant filename convention specified in Table A-1. Table A-1 – Filename Format Item Format Structure <substation name> <voltage> Earthing <type> (<report number> <revision number>) Substation Name From earthing database in title case e.g. Brighton Town Voltage All voltages on-site separated by dashes e.g. 11kV, 33-11kV, 132-33-11kV etc. Type Earthing EPR Assessment Report Earthing Survey & Assessment Report Earthing Layout Drawing Earthing Layout Drawing – Proposed Report Number Unique report of drawing number in brackets Version or Revision Number Not required for original versions, include in brackets with report/drawing number e.g. r1, rA etc Examples: Brighton Town 132-33-11kV Earthing EPR Assessment Report (ESL000000-R01).pdf Brighton Town 132-33-11kV Earthing Survey & Assessment Report (ESL000000-R01).pdf Brighton Town 132-33-11kV Earthing Survey & Assessment Report (ESL000000-R01 rA).pdf Brighton Town 132-33-11kV Earthing Layout Drawing (ESL000000-D01).pdf Brighton Town 132-33-11kV Earthing Layout Drawing - Proposed (ESL000000-D02).pdf © UK Power Networks 2016 All rights reserved 10 of 11 Earthing Assessment Process Document Number: EMS 10-0602 Version: 1.0 Date: 12/09/2016 A.2 PDF Properties The File and Title pdf properties should follow the convention specified in Table A-2 to allow trouble free uploading into Alfresco. The pdf properties can be displayed via File > Properties however these may have originated from the source document or drawing file. Table A-2 – PDF Properties Property Content File Match filename Title Blank A.3 Dates All dates shall use the format specified in Table A-3. Ordinals e.g. th, st, rd etc. shall not be used in dates. Table A-3 – Date Format Location Format Tables dd/mm/yyyy Main body dd mmmm yyyy © UK Power Networks 2016 All rights reserved 11 of 11