Research Status & Deliverables

Research Status of a Selection of Tasks

Task: Improving the Mechanical Durability of TLSA Lead
Task Description: Non-Gapped Line Arresters (NGLA) are often applied to improve the lightning performance of transmission lines. While these transmission line surge arresters (TLSA) may perform well electrically, their installation is often compromised by failures of the connection leads or the disconnector. A new lead design was developed to avoid those early failures. This task intends to document the lab performance of the new design, and to continue the field trials to identify potential early issues. This may result in a best practice for the installation of transmission line surge arresters with new specifications.
Update:

• The new lead attachment design shows promising mechanical performance from the test results performed with the stainless steel lead but this doesn’t seem as promising when a copper lead is used with the new attachment.
• The thermal performance of the stainless steel lead could be coordinated with the disconnector in case of a surge arrester failure, but the lead temperature could continue to rise if some current is still applied after the disconnector operation (arc maintaining the connection). A more conductive lead would be preferred.
• Mechanical testing is being planned with a copper clad steel lead and the new attachment design.

Task: Improved Lightning Shielding Failure Approach for Tall Structures
Task Description: Since the introduction UHV lines with tall support structures, utilities have experienced a significantly high number of lightning outages caused by shielding failures. The shielding failures in most cases are not predicted by the traditional calculation methods. This task aims to improve the lightning strike attraction models and benchmark the new approach against documented cases of shielding failures. If proven valid, the newly developed algorithm is intended to be included in EPRI’s Lightning and Grounding prediction software TFlash.
Update:

• The implementation has then been applied on a set of 202 kV and 400 kV transmission lines with lightning correlated outages. The predicted shielding failure flashovers were completely underestimating the observations.
• Two outages on a 765 kV line correlated with lightning events by a Lightning Location System were studied. The outages were associated to low values of lightning peak current (indirectly measured) which indicates that they could have been shielding failure flashovers. The simplified Rizk model was applied for those lines with positive results.

Task: Lightning Arc Damage to OPGW
Task Description: In recent years, utilities are increasingly experiencing damage to optical fiber ground wires (OPGWs) caused by lightning strikes to the ground wire. In some cases, severe damage to the OPGW could result in failure of the communication link or mechanical failure of the ground wire. This task intends to review the sizing method of OPGW regarding lightning arc damage and the associated test protocols commonly used by utilities.
Update:

• The typical approach to estimate the class of the OPGW for the Lightning Arc Test in the standard IEEE 1138 has been reviewed and improvements and limitations have been identified.

• A sample of failed OPGW has been received and some lightning arc tests are being planned to study the impact of the amount of transferred charge on the damage pattern and residual strength.

  
  

Task: Increased Information When Performing HF Grounding Measurements Task Description: Most ground testers measure the low frequency grounding resistance which may not be relevant for lightning. However, there can be a significant difference between the low and high frequency value of the ground electrode. This task intends to extract additional information from high frequency measurements of transmission line ground electrodes. This information may help to validate the quality of the measurements and improve interpretation of the results. Finally, the intention is to provide a framework for creating a transient model of the ground electrode based on the high frequency measurements.
Update:

• An alpha version of the analysis method was implemented.

• New field measurements were performed with both the Zed-Meter and a directional tester on a lattice structure.

• The method to measure the distance between the remote potential probe and the structure was reviewed. New best practices were identified to improve the accuracy of Zed-Meter measurements with the oblique method.

  
  

Task: Surge Arrester Failure Database and Analysis Task Description: This task collects information about transmission line surge arresters (TLSA), either in-service, failed or post laboratory analysis. The centralized collection of this information helps revealing failure trends that may otherwise not be apparent. This information is used as an important tool for fleet management and the initial start of research projects. Performance information is available on EPRI’s Industry Wide Database IDB
Update:

• New charts were developed to analyze dynamically the content of the database and will soon be available.

• The DC assessment test has been improved to automate the interaction with the high voltage supply and allow for more data points to be gathered when assessing the state of a surge arrester.

  
  

Planned 2024 Deliverables

2023 Deliverables

Key Deliverables