As elaborated in our previous post, Dynamic Contact Resistance Measurement (DCRM) tests play a pivotal role in preventing unexpected failures of High Voltage (HV/EHV/UHV) Circuit Breakers by cohesively assessing the healthiness of their contacts.
Widely considered as the most comprehensive CB testing methodology, the success of any DCRM test depends on a trifecta of the right DCRM Kit, superior analytical skills, and in-depth knowledge of the CB design, its various operating mechanisms, etc.
In this post, we’ll highlight how SCOPE T&M Pvt. Ltd. helped one of India’s largest Electric Power Transmission Utility companies safeguard their power infrastructure by preventing CB failures through expert DCRM testing.
As part of their annual routine maintenance exercise, our client wanted to test their 420kV SF6 CB that was in service for over 6 years and used a spring-spring based operating mechanism.
Since the CB was connected to the Tie-Bay, it had Current Transformers (CTs) installed on both its sides.
SCOPE was roped in to conduct a comprehensive non-invasive DCRM testing of this CB to assess its operational healthiness.
Our DCRM Expertise
Using our state-of-the-art DCRM Kit ‘HISAC Ultima’, we initiated DCRM testing and observed the below abnormalities in the DCRM Signature:
1. A higher number of bounces in the ‘R’ phase on the CT1 side interrupter as depicted below.
2. A higher contact resistance on both sides of the interrupter for the ‘Y’ phase as depicted below.
Based on the above two DCRM results, our client asked the CB’s OEM team to open the CB for fault identification.
Upon dismantling the CB, the below two defects were identified:
1. The moving contacts of all the four interrupters had heavy carbon deposits as depicted below:
2. The Teflon-coated nozzle was punctured in the ‘Y’ phase of the CT2 side as depicted below:
Corrective Measures Taken
1. The punctured nozzle on the ‘Y’ phase CT2 side of the interrupter was replaced; and as a precautionary measure, the nozzle on the CT1 side of the interrupter was also replaced.
2. The moving contacts were thoroughly cleaned to eliminate all the carbon deposits.
On completion of the above two rectifications, the DCRM test was repeated to assess the impact of the rectifications and the resulting DCRM Signatures were found normal.
Here is a quick snapshot of the ‘before’ and ‘after’ DCRM Signatures:
1. ‘R’ phase CT1 Signature
2. ‘Y’ phase CT2 Signature
As organisations restart their business activities in full swing after the COVID-19 lockdown is lifted up, Utility companies should gear up for a sudden surge in electricity demand.
To keep the grids functioning smoothly in the wake of this sudden surge in demand, Circuit Breakers will now play an increasingly important role. And to ensure that these Circuit Breakers don’t fail when they are needed the most, DCRM testing to assess their operational healthiness becomes pivotal.
To learn how SCOPE’s DCRM expertise can help Utilities ensure optimal functioning of their power infrastructure, please write to us at firstname.lastname@example.org and we will get back to you in a jiffy!