Transformation in lifetime asset management of EHV circuit breakers - a case study

Indian power sector has seen aggressive growth in last decade and is expected to grow even more in coming years. As the number of assets in EPU substations are being added, Life Cycle management of these assets is a great challenge. Indian Power System has thousands of EHV Circuit Breakers (CB), which operate frequently as per system requirements. CBs being critical equipment in EHV substations, their outages have considerable economic impact. As the CB failure rate was quite high, an urgent action to contain CB failures was necessary. Each CB failure was analysed critically under strategic collaborative efforts among EPUs, CB OEMs and Testing Instruments manufacturer in India to study reasons & contain CB failures. Gradually condition assessment test “DCRM” for new circuit breakers at OEMs & for CBs in service was introduced. Now CB failure rate has drastically reduced & is within acceptable international norms.

This paper describes the transformation journey for Life Cycle Monitoring & Management of EHV CBs during past 20–25 years in Indian Power Sector as an interesting Case study. Three stages of this transformation journey as mentioned hereunder with key takeaways are captured in this paper.

Stage I: Preventive Maintenance using Off-Line CB Timers/CB Analysers

CB failure rate in India was high in late 90s & early 2000. The health monitoring of CBs then involved periodical preventive maintenance testing conducted generally by using CB Timers and subsequently CB Analysers. The measurements like Main & PIR contacts operation timings, coil currents & sometimes travel related parameters were conducted. The records of such testing were kept.

Stage II: Condition Based Maintenance using Off-Line CB Analysers with DCRM

In-spite of periodical testing by using above mentioned tools, there were many CB failures. It called for detailed assessment of causes of failures. Powergrid Corporation of India Ltd. (POWERGRID), the Indian CTU studied the failures and identified that the above parameters are not adequately reflecting the healthiness of all components of CB, especially the healthiness of main & arcing contacts assembly, mechanism linkages etc., which contributed significantly to failures. This led to development of DCRM, Dynamic Contact Resistance Measurement.

DCRM coupled with travel measurement started revealing many weaknesses hitherto hidden. DCRM was conducted across the POWERGRID on all CBs from 132 kV to 765 kV, and many CBs were opened based on DCRM results. He findings corroborated the predictions of DCRM measurement. It became the true reflector of condition of CB and paved way for Condition Based Maintenance (CBM) instead of time based maintenance. It significantly brought down the failure rate of CBs and is toady within acceptable international norms. DCRM is now accepted world-over and is also being included in international standards.

Stage III: On-Line Monitoring of EHV CBs

Huge growth in Indian power system network has paved way for many new EHV transmission lines of 765 kV AC & 800 kV HVDC, with 1200 kV AC under experimental implementation. The numbers of assets are significantly increasing. The demand of availability is 99.9% in India. This means, on one hand it is becoming more & more important to ensure the reliability & up-time of all components involved and on the other, it has become very difficult to take planned shutdowns for conducting periodical testing. This has necessitated the development of on-line monitoring solutions as reliable means of on-line, real time feedback on the condition of CBs in use.

The future will consist of widespread implementation of On-line CB Monitors facilitating local as well as centralised asset monitoring. And any abnormality in any of the performance parameter can be further investigated by using off-line diagnostic instruments.