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Assessment of Expected Service Life of Relays

Project Objective

Hydro One Networks Inc. (HONI) periodically submits rates filings to the Ontario Energy Board (OEB). These submissions inter alia detail their key asset needs based on asset age, condition assessment, performance and other relevant factors that lead to asset replacement or refurbishment.

Electromechanical, solid-state and digital/numerical relays are transmission station assets that play a critical role in ensuring safe and reliable operation of the transmission system. In addition to the condition, functionality and maintenance records, in the past, the decision to refurbish or replace relay sub-populations has been predominantly based on age vs. deemed expected service life (ESL).  Age is gaining even greater influence as a replacement criterion due to the fact that it is more difficult to determine deterioration of digital relays compared with older technologies. In order to be able to use aged components with better accuracy, HONI approached Kinectrics to perform an independent study of the deemed ESL. 

The objective of this project was to assess the ESL for two representative relay models in their inventory using accelerated life testing, where the information from this assessment could be used as an input by asset managers for their asset life-cycle strategy.

Scope of Work

A solid-state and a digital/numerical based relay were selected as representative models within five years of their deemed ESL. The scope of work entailed:

  • Determining a reliability target with associated confidence level vs. availablenumberof specimens per model
  • Compiling a bill-of-materials (BOM)

  • Determining acceleration factors at the component level

  • Planning an appropriate test regime

  • Temperature-based accelerated life testing with pass/fail detection and results analysis

Work Performed

Target reliability is expressed as the survivability (reliability) of the sub-population for a specified number of years beyond achieved age. The field-removed specimens were subjected to several ‘heat soaks’ to accelerate aging along with periodic functional performance testing to confirm that they were in still in working order and operating within specification.



The project was a success having been executed on time and on budget against an aggressive timeline to meet HONI’s rates filing deadline. The client was pleased with the level of detail and rigor in the real-world testing performed by Kinectrics. The test results demonstrated that the two representative relay models in their inventory will have a higher survival rate in the near to mid-term period. The results allow HONI to adjust their asset life-cycle strategy in which HONI have flattened out the replacement plan for the respective relay models over a longer period. ​​​
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