Introduction: Bushings pose a challenge in assessing their condition and determining a meaningful asset health index, which would assist in the management of this asset class. Even when oil sampling can be performed this is carried out on a very infrequent basis as they are typically inaccessible even during outages without scaffolding for the purpose of taking a sample. For dry-type bushings there is no oil to sample. Consequently alternative methods of assessment are required, which would ideally allow more frequent assessment of condition. This project will apply online bushing monitoring on a continual and temporary basis to assess the relative benefits of each. The project will further consider the advantages simultaneous partial discharge (PD) monitoring brings to the assessment of the bushing but more broadly to other connected assets.
Although this project will focus on transformer bushings, the technology may applied to through wall bushings.

Objectives: To provide National Grid with the knowledge to be able to undertake condition assessment programmes of solid type bushings based on onsite condition monitoring measurements, and to provide tools to detect early bushing deterioration and prevent catastrophic failure.

Expected Benefits: At present the strategy for ERIP bushings is to replace at end of anticipated life at an estimated 40 years. National Grid has 189 ERIP bushings between 25 and 40 years old installed on transformers (out of a total population of 289 ERIP transformer bushings) and understanding the deterioriation of condition as they approach end of life could result in life extension. The same technology could potentially be extended to ERIP wall bushings
In the event that monitoring ERIP assets can defer replacement an average of 10 years this would defer capital investment of £12.6 m for 10 years from 2025 to 2035.