TITLE:
Condition Assessment of Medium Voltage Gas Insulated Ring Main Unit Using Health Index
AUTHORS:
Raja Saharuddin Raja Daud, Muhammad Sharil Yahaya, Hidayat Zainuddin, Arfah Ahmad, Norhafiz Azis
KEYWORDS:
Health Index, Gas-Insulated Ring Main Unit, Condition Monitoring, Risk Factor, Condition Assessment
JOURNAL NAME:
Journal of Power and Energy Engineering,
Vol.13 No.9,
September
3,
2025
ABSTRACT: This paper presents a study on the formulation of a Health Index (HI) to assess the condition of gas-insulated Ring Main Units (RMUs). A total of 250 condition monitoring records for 11 kV distribution Ring Main Units (RMUs), aged between 1 and 27 years, were obtained from a Malaysian utility operator, with the sample randomly selected from a central region state that has the highest concentration of RMU assets in the country. The development of the HI algorithm was based on scoring, weighting, and ranking techniques. In addition to the HI, a risk factor was introduced to enhance the accuracy of the final HI estimation. Condition monitoring (CM) data were gathered using condition-based monitoring (CBM) techniques such as thermal scanning, ultrasonic testing, transient earth voltage measurement, SF6 gas level monitoring, and visual inspection. The ranking, weighting, and scoring for each parameter were determined based on expert assessments, utility practices, and relevant standards. The risk factor was established by considering environmental conditions, Original Equipment Manufacturer (OEM) data, and the risk of ageing mechanisms. Subsequently, the final HI for each CM data set was calculated. The findings showed that the HI approach can effectively be used to assess the condition of RMUs based on CM data. A statistical analysis of the 250 RMU records revealed that 44% of RMUs have a high HI, 51% have a medium HI, and 6% have a low HI. This indicates that the maintenance cycle for 44% of the RMUs can potentially be extended. The results are expected to support the development of optimized maintenance planning and cost management strategies.