UP-RATING OF OVERHEAD LINES

Lead Research Organisation: Cardiff University
Department Name: Sch of Engineering

Abstract

The ever increasing demand for electricity consumption accompanied by environmental pressures impose a continuing need for electrical systems modification and growth, partly because of changing operational practices resulting from de-regulation and, partly, due to the increased use of distributed generation, which is changing the demands on transmission and, especially, distribution lines. But for many years now, the opportunities for installation of new lines have become very limited because of public concern over visual and other environmental impacts, and it is clear that extensions to system capacity will have to be met substantially without new lines.The voltage rating and the insulation coordination of transmission and distribution lines is determined by a combined consideration of the voltage stress applied to the line and its electrical strength. The stress arises from overvoltages due to switching transients or lightning surges. The magnitude of the switching overvoltage is controlled by the characteristics of the system components, and is more critical at the highest operating voltages. Lightning overvoltages, on the other hand, are of much larger magnitudes and are more onerous to distribution systems.IEC 60071 makes recommendations for the gaps and clearances to be used for specific voltage levels, and individual operators will then adopt safety factors above and beyond these recommendations, depending upon local conditions. Pollution, for instance, may reduce the breakdown voltage by up to 50%. These adopted clearances are usually very generous and can be optimised using modern equipment and practice.The investigators have researched for many years the possibilities for compact lines and substations through improved co-ordination of insulation and the use of polymeric insulators and more effective protective devices such as ZnO surge arresters. This programme, therefore, proposes to apply the compact line concepts to the up-rating of existing lines. It will involve statistical studies of switching and lightning surges that account for various parameters which affect the overvoltage magnitudes, such as closing times for circuit breakers and analysis of the possible state of the line in order to minimize the risk of re-closing onto trapped charge. The statistical variations of stress and strength of the system will be combined in a voltage-frequency plot to determine the risk of failure, which has to be minimized within economic constraints. The stress will be presented as the probability of a certain overvoltage occurring, and its distribution along a line will be controlled by the judicious placement of modern ZnO surge arresters. Electrical strength, on the other hand, can be presented as a probabilistic breakdown curve. It will be primarily derived from consideration of the breakdown curves taking into account the critical clearances at the tower and along the line. These principles have been studied over the years, but present-day pressures are causing a re-evaluation of the conventional limits and methodology. This is also supported by the excellent performance of modern ZnO surge arresters in controlling overvoltages and the superior pollution performance of new polymeric insulators. The programme will also include laboratory and field experimental programmes to test and characterise the new devices and configurations to be used for the compact design of the uprated lines. The main output of the programme is to establish well researched fundamental principles that will allow an efficient and safe design for the future transmission and distribution lines.The basis of this programme has been proposed by HIVES, Cardiff University and then moderated by discussions with an industry group involving National Grid, four UK DNOs, ESB and three line construction companies, whose views are embedded in the proposed programme.
 
Description current electrical clearances, as applied on the electrical network are very reliable because they include a suitable margin to ensure voltage withstand. however, these can be reduced significantly if overvoltage protection is used, and hence savings can be achieved.
Exploitation Route Future compaction of electrical systems and new designs of air insulated equipment/systems can take advantage of the compaction/uprating concepts established in the projects. such application was already used in compact substation design and the new T-pylon
Sectors Energy

 
Description The knowledge and findings of the research project were applied in a research project for National Grid which studied the electrical performance of the new T-Pylon transmission lines. This type of line is now being tested at Eakring training Centre. the new line is expected to be first used in the west country, possibly after 2016.
First Year Of Impact 2012
Sector Energy
Impact Types Economic

 
Description particpation in CIGRE technical working groups and IEC standards committees
Geographic Reach Multiple continents/international 
Policy Influence Type Membership of a guidance committee
 
Description CF3I gas and mixture as an alternative to SF6
Amount £105,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 10/2010 
End 03/2014
 
Description Centre for integrated renewable energy generation and supply (CIREGS)"
Amount £3,600,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 01/2008 
End 06/2013
 
Description Compact substations and conductor systems
Amount £210,000 (GBP)
Organisation National Grid Transco 
Sector Private
Country United Kingdom
Start 10/2006 
End 10/2009
 
Description Determination of effects of reactive power compensation on distribution networks: steady state and transient studies
Amount £46,000 (GBP)
Organisation Western Power Distribution 
Sector Private
Country United Kingdom
Start 04/2012 
End 07/2013
 
Description Earthing measurement techniques and apparatus
Amount £55,000 (GBP)
Organisation Megger Group Limited 
Sector Private
Country United Kingdom
Start 04/2007 
End 03/2010
 
Description Electrical Performance of the T-Pylon
Amount £138,000 (GBP)
Organisation National Grid Transco 
Sector Private
Country United Kingdom
Start 01/2013 
End 12/2013
 
Description Enhanced ACDC safety volatage limits
Amount £216,000 (GBP)
Organisation National Grid Transco 
Sector Private
Country United Kingdom
Start 04/2014 
End 06/2016
 
Description Feasibility of using trifluoromethyl iodide as a replacement for sulphur hexifluoride in high voltage switchgear
Amount £25,000 (GBP)
Organisation National Grid Transco 
Sector Private
Country United Kingdom
Start 03/2009 
End 06/2009
 
Description Gas insulated lines for electrical power transport
Amount £15,000,000 (GBP)
Organisation Government of Wales 
Department Welsh European Funding Office
Sector Public
Country United Kingdom
Start 06/2016 
End 07/2020
 
Description Impact of offshore networks on the insulation coordination and operation of the NG transmission system
Amount £150,000 (GBP)
Organisation National Grid Transco 
Sector Private
Country United Kingdom
Start 07/2009 
End 06/2012
 
Description Innovation in high voltage electrical insulation of electrical energy systems"
Amount £17,000 (GBP)
Organisation UK-India Education and Research Initiative (UKIERI) 
Sector Academic/University
Country United Kingdom
Start 04/2012 
End 12/2014
 
Description Lightning effects on aerospace carbon composite materials, the next generation of materials and components
Amount £761,000 (GBP)
Organisation Government of Wales 
Department Welsh European Funding Office
Sector Public
Country United Kingdom
Start 09/2013 
End 12/2014
 
Description Low Carbon Research Institute & CIREGS
Amount £610,000 (GBP)
Organisation Welsh Assembly 
Sector Public
Country United Kingdom
Start 04/2008 
End 03/2013
 
Description Materials and advanced engineering knowledge exchange strategy (MAeKES)"
Amount £20,000 (GBP)
Organisation Government of Wales 
Department Welsh European Funding Office
Sector Public
Country United Kingdom
Start 01/2013 
End 11/2014
 
Description Measurement of third party exposure to rise of earth potential (ROEP)"
Amount £62,000 (GBP)
Organisation Scottish Power Ltd 
Sector Private
Country United Kingdom
Start 10/2007 
End 08/2009
 
Description Measurement of third party exposure to rise of earth potential"
Amount £100,000 (GBP)
Organisation National Grid Transco 
Sector Private
Country United Kingdom
Start 09/2009 
End 09/2010
 
Description Online detection and location of defective overhead line components using travelling wave transients"
Amount £129,000 (GBP)
Organisation Knowledge Transfer Partnerships 
Sector Private
Country United Kingdom
Start 04/2009 
End 03/2011
 
Description Optimised location for surge arresters on the transmission network
Amount £60,000 (GBP)
Organisation National Grid Transco 
Sector Private
Country United Kingdom
Start 09/2012 
End 04/2013
 
Description The National Grid Transco High Voltage Research Centre
Amount £225,000 (GBP)
Organisation National Grid Transco 
Sector Private
Country United Kingdom
Start 01/2011 
End 12/2013
 
Description The National Grid Transco High Voltage Research Centre - Additional funding
Amount £103,000 (GBP)
Organisation National Grid Transco 
Sector Private
Country United Kingdom
Start 07/2009 
End 12/2010
 
Description Transformation of the top and tail of energy networks
Amount £521,000 (GBP)
Funding ID EP/I031707/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 10/2011 
End 09/2015
 
Description overhead line monitoring system (OHMS)
Amount £105,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 10/2008 
End 04/2014
 
Description Babcock International Group Plc 
Organisation Babcock International Group
Country United Kingdom 
Sector Private 
Start Year 2007
 
Description Balfour Beatty Power Networks 
Organisation Balfour Beatty
Department Power Transmission & Distribution
Country United Kingdom 
Sector Private 
Start Year 2007
 
Description E.On UK Plc 
Organisation E ON
Department E ON UK
Country United Kingdom 
Sector Private 
Start Year 2007
 
Description National Grid 
Organisation National Grid Transco
Country United Kingdom 
Sector Private 
Start Year 2007
 
Description SP Power Systems Limited 
Organisation SP Power Systems Limited
Country United Kingdom 
Sector Private 
Start Year 2007
 
Description several magazine, newspapers, radio and TV (CNN, BBC Discovery...)programmes on lightning protection of aircraft 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact better understanding of lightning impact on aircraft

Various organisations and media visit the lab regularly
Year(s) Of Engagement Activity 2011,2012,2013,2014