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JWG A3.32 / CIRED – Non-intrusive methods for condition assessment of distribution and transmission switchgear

The changing nature of the power system due to the rapid roll out of renewable and distributed generation presents a risk of unnecessary expenditure on infrastructure.  New technologies that collect much greater data on system performance and innovative approaches that minimise equipment outages can reduce this risk.  Non-intrusive condition equipment assessment, which can be carried out with the equipment in service, reduces the potential for customer outages as well as unnecessary duplication and inappropriate replacement of equipment. CIGRE/CIRED Joint Working Group A3.32 recently produced Technical Brochure 737.  The publication analyses the state of the art of non-intrusive condition assessment methods and associated field experience applied to circuit breakers, reclosers and fault interrupters for both transmission and distribution switchgear. The Australian member of this working group was Jose López-Roldán.

For users of switching equipment, knowledge of the equipment condition is key to preventing unforeseen equipment failures and outages, which may affect production and also have safety, reliability and financial implications. Under the Australian Energy Regulator environment, it is a requirement for TSO/DNO’s to justify the need for replacement of equipment, which can be due to many factors, including the overall asset condition, and not solely based on age. Measurement and assessment of the equipment condition can take many forms depending upon the different equipment type on the networks.  For static equipment such as switchboards the condition assessment may take the form of operating temperature measurement and condition monitoring of the insulation. For equipment such as circuit breakers and reclosers which rely on operating mechanisms and other moving components along with the insulation, condition assessment of the speed of operation, contact resistance, control system integrity and other insulation monitoring is required to determine the condition of the equipment.

TB 737 provides a review of fifty-five diagnostic methods, which are designed to operate on equipment non-intrusively. Forty-one methods are installed non-intrusively, nine require a minimal intrusive installation and five are intrusively installed. Of the methods listed, thirty-nine of the fifty-five methods can be installed with the equipment in-service.  Many of the methods are quite mature in their use. Reviewed diagnostic methods cover:

  • Application;

  • Mode of application;

  • Theoretical background of operation

  • Degree of maturity, and

  • Ease of use and constraints.

TB 737 recommends that appropriate cost benefit analysis is carried out on the condition assessment methods intended to be used. Benefits of the diagnostic methods can be expressed in terms of condition indicators and the potential achievable diagnosis. The cost analysis involved with the total expenses of procuring and installing the diagnostic methods along with the data gathering and overall condition assessment analysis are also covered in the TB.

TB 737 presents state of the art methodologies to assess the technical and economic benefits of non-intrusive condition assessment methods. All the methods compare three main cost elements:

  1. Investment in the condition assessment system;

  2. Cost of failure/outage with and without condition assessment (Involves risk assessment)

  3. Cost of maintenance with and without condition assessment.

Overall, the definition of the end of life of the asset is critical for the evaluation of condition assessment benefits based on the actual asset condition, instead of using statistics, asset failure models or simply asset age. The better the condition of an asset is known, the more effective it is to schedule individual maintenance, or to initiate refurbishment or replacement of critical assets while deferring action on assets still in a healthy condition.

The Technical Brochure (TB) 737 can be viewed on e-CIGRE and is free to members. The cost to non-members is €390.