National Grid recognises that the challenges faced by the electricity industry can be more efficiently and cost-effectively addressed when approached through international collaboration initiatives. It is particularly useful when addressing challenges where the solutions require statistically diverse data sets and/or significant trialling and testing in different environments, under various conditions and/or diverse ways.
The Electric Power Research Institute (EPRI), with its wide international membership, is one of the routes through which these initiatives can be delivered, thereby maximising stakeholder value. The approach of managing collaborative projects within an internationally driven research and development initiative is beneficial to National Grid and consumers alike, because it provides valuable information, learning and knowledge that would be considerably more expensive if approached on an individual basis.
As an owner of overhead lines, National Grid faces challenges around optimisation, asset life, development of innovative and fit for purpose monitoring, maintenance practices and understanding what novel technologies could be applied to improve efficiencies. The EPRI Overhead Transmission Lines Programme 35 (P35) aims to develop this work via five supported project work-streams.
Following an assessment of our internal Overhead Line strategy and an internal review, National Grid determined that within EPRIs Overhead Transmission programme, the largest leverage for the UK consumer can be achieved through involvement in the following five projects during the period 2018-2021:
P35.001 - Inspection, assessment and asset management of overhead transmission lines
P35.002 - Conductor, earth wire and hardware corrosion management
P35.003 - Structure and Sub-Grade Corrosion Management
P35.011 - Polymer and composite overhead transmission insulators
P35.013 - Overhead line ratings and increased power flow
P35.015 - Qualification, selection and maintenance of advanced conductors
The work areas have outputs that span across multiple years, consequently, this project will benefit National Grid and our stakeholders by committing to deliver the research activities of P35 over three years.
Objectives
The objectives for the 2018-2021 period include the continuation of National Grid’s membership with EPRI P35 and the delivery of a selection of reports and guidance documents associated with the five work-streams by undertaking the following tasks:
P35.001 - Inspection, assessment and asset management of overhead transmission lines
Overhead Transmission Line Inspection, Assessment and Asset Management Reference Guide (Yellow Book):
Yellow Book Browser Application (Software)
Overhead Transmission Line Inspection – Online Training (OTLOT) Version 2018
Overhead Transmission Inspection and Sensing Information Tool (OTIS) Version 2018
Practical Inspection and Assessment Workshop
Overhead Transmission Line Field Guides
P35.002 - Conductor, earthwire and hardware corrosion management
Assess and evaluate new and emerging inspection technologies including non-contact and ground based inspection
understanding the potential of using near infra-red (NIR) spectroscopy to determine degradation rates and remaining conductor life
Develop corrosivity models using algorithms for aging and atmospheric exposure of conductors and hardware and correlate results though lab and field testing
continued development of NIR spectroscopy technology application for condition assessment of degraded hardware or component surfaces
P35.003 - Structure and Sub-Grade Corrosion Management
Corrosion probe inspection tool for sub-grade corrosion evaluations
Coating system selection and application guidelines
Corrosion education
Fleet management
Failure database
Concrete foundation mitigation and remediation methods
P35.011 - Polymer and composite overhead transmission insulators
multi-stress ageing tests to understand various modes of degradation and performance of polymer components National Grid has commissioned EPRI to carry out accelerated aging tests on a range of polymer insulators at various stages over the last 15 years. These tests are planned to continue for several years more to provide reliable information on long term performance alongside some ongoing field trials on the NG network. In addition to this National Grid are also able to receive benchmark data across a broader field of suppliers
continued development of the failure database to help identify trends and attributes to failures
developing short duration, small scale tests that are representative of in-service stresses. The tests may be included in utility specifications
inspecting service-aged insulators to aid in understanding how insulators age and the factors of aging which in turn helps improve applications and improve reliability and performance
development of E-field modelling software to help model the electric field on new or existing insulator designs.
P35.013 - Overhead line ratings and increased power flow
Development of software tools
Development of rating methodologies
Development of guidebooks, reports, and training materials for implementing increased power flow strategies, and for training engineers on increased power flow technologies.
Comparison of economic benefits of increased power flow technologies, enabling utilities to make informed decisions when choosing options for their specific applications.
P35.015 - Qualification, selection and maintenance of advanced conductors
Developing an HTLS conductor application guide.
Developing a test protocol to compare different carbon fiber composite core conductors
Provide information on comparing and selecting suitable HTLS conductors for specific applications.
Developing maintenance procedures and recommend that can be incorporated into utility’s maintenance manuals.
Testing the thermal and mechanical performance of these HTLS conductors.
Learnings
Outcomes
Some of the key outcomes of this project are:
P35.001 - Inspection, assessment, and asset management of overhead transmission lines
- Multiple Mobile Field Guides
- 3002018874 - Overhead Transmission Inspection, Assessment, and Asset Management Reference Guide 2020 (Yellow Book)
- 3002018876 - Yellow Book Browser Application (YBB) 2020
- 3002018871 - Overhead Transmission Inspection and Sensing Information Tool (OTIS) Version 2020
P35.002 - Conductor, earth wire and hardware corrosion management
- 3002018887 - Atmospheric Corrosion Sensors Overview: Vision of Use
- 3002018886 - Fleet Management for ACSR & ACSS Conductors: Optimizing Conductor Inspection Program
- 3002018885 - C-Corr Performance and Operations Evaluation
- 3002018882 - Forensic Analysis of Conductors
P35.003 - Structures and Sub-Grade Corrosion Management
- 3002018889 - Coating Selection and Application Guidelines for Transmission Fleet Management
- 3002018890 - Fleet Management for Structural Corrosion
- 3002018897 - Transmission Line Structure Foundation Management: Concrete and Engineered Backfill Guidelines
- 3002018899 - Guidelines for EPRI Corrosion Test Protocols: Inspection, Assessment, Mitigation and Forensics
P35.011 – Polymer and composite overhead transmission insulators
- 3002019072 - E-field Modeling Software (ICE -Insulator Calculation Engine)
- 3002019075 - Polymer Insulator Population Assessment (PIPA) Software
- 3002019078 - High Voltage Indoor Aging Chamber Report
- 3002019081 - ADSS Application Software
- 3002019073 - Insulator Reference Book
- 3002019079 - Summary of lessons learned on Failure Analysis of Polymer Insulators
P35.013 - Overhead line ratings and increased power flow
- 3002019088 - Update on Conductor Emissivity and Absorptivity Database: Summary of Testing 2006 – 2020
- 3002020158 - Summary of Recent Increased Transmission Line Utilization Projects: 115 kV and Above
- 3002019087 - Summary of Weather Data Measurements and Modelling: Use in Real-time and Forecasted Line Rating
- 3002019086 - Increased Power Flow Guidebook: 2020
- 3002019085 - TRW (Transmission Rating Workstation) – Final 2020 Version
P35.015 - Qualification, selection and maintenance of advanced conductors
- 3002019096 - Guide for Selection and Application of High Temperature Conductors: HTLS Standards
- 3002019099 - High Temperature Mechanical Performance
- 3002019098 - ACSS versus ACSR Vibration Performance: Thrasher Conductor
- 3002019097 - Qualification Test Report Update
Lessons Learnt
P35.001 - Inspection, assessment, and asset management of overhead transmission lines
Despite the vast number of inspection tools available, most inspection crews continue to use traditional approaches to routine transmission line inspections. Support is required to embed new methods into BaU.
Although more satellites are being placed into orbit than in any previous era, and imaging capabilities are improving, they are limited to larger right-of-way infractions and changes.
P35.002 - Conductor, earth wire and hardware corrosion management
New methods to identify and quantify fretting corrosion have been developed for conductors and hardware with the corrosion rates categorised as high as C5 in a C2 environment. Study to evaluate the impact of corrosion on service life of dampers is planned for future works.
P35.003 - Structures and Sub-Grade Corrosion Management
A range of coating systems were tested in a laboratory environment that helped in establishing minimum performance thresholds for extended service life. Depth of carbonation by coring and potential of rebar in concrete were developed as additional inspection and assessment techniques for concrete foundation management.
P35.011 – Polymer and composite overhead transmission insulators
3-year and historical failure trends in polymer insulators indicate reduction in brittle fractures and flashunders but steady occurrence of mechanical failures and destruction of rod were observed.
P35.013 - Overhead line ratings and increased power flow
Field trials comparing outputs of line monitoring devices that contribute to (dynamic line) rating calculations with actual field measurements indicate that considerable risks are associated with enhanced ratings obtained from monitoring. Each utility was recommended to develop a risk-based framework to assess such risks on ratings.
Correlation of Weather Variables: Existing weather models do not accurately account for factors that drive rating risks. Weather models need to be aligned with field measurements to improve accuracy. When making weather measurements for ratings, weather stations may need to be 10 miles apart or less.
P35.015 - Qualification, selection and maintenance of advanced conductors
Initial testing indicates that ACSS conductors have inherently more self-damping capability than the equivalent (same diameter and stranding) ACSR conductor. The original finding was confirmed by a second set of tests conducted in 2020
The qualification test of a carbon core conductor showed that the mechanical performance of carbon core conductors can be affected by the surface coatings used on the outer surface of the core. These coatings are typically used to ensure a physical barrier between the carbon core material and the outer aluminium strands.
