Case Study 1 – Partial Discharge Activity at Transformer
During a routine partial discharge scan at one of our client’s premises, an abnormality was detected when performing ultrasonic PD measurement at the dry type transformer.
PD activity on Ultrasonic PD mode (before)
The issue was promptly highlighted and reported, with recommendations to shutdown the affected transformer for further investigation and rectification. Based on the location and PRPD pattern, it was hypothesized that the PD was a surface discharge, and the likely sources were from
- Transformer HT Winding
- HT cable or HT terminations
I2R promptly assembled a team to design procedures and solutions to investigate the root cause and resolve the PD abnormality.
Firstly, we carried out a Load profile trending study to evaluate the power Redundancy of the Electrical Installation. An alternative source was identified as a viable option for load transfer in the event the affected Transformer is out of service.
Load profile trending for L1 phase
Next, our team coordinated with the client for a suitable window and I2R’s LEW performed Electrical switching and load transfer operations to shut down the affected Transformer. Upon shutdown of the Transformer, a visual Inspection of the transformer’s internal was done to check for any abnormality. During the inspection, a discolouration was observed on L1 phase of the HT cable termination at the Transformer cable end.
L1 Phase of HT cable termination
To confirm the result, diagnostic tests were performed;
- HT Cable VLF and Tangent Delta test to check the condition of the HT cable and terminations
HT Cable tangent Delta test
Transformer Winding Resistance test, Transformer Turns-Ratio test, Transformer Tangent Delta test and Power Frequency High Voltage test was carried out to test the condition of the Transformer.
Transformer turns ratio test
Transformer Winding Resistance test
The team evaluated the tests results and judged that the likely source of the PD was from the HT Cable termination, a certified cable jointer was promptly engaged to replace the cable terminations.
HT Cable VLF and Tangent Delta test was performed after the replacement work to confirm the results post-rectifcation. The results showed an improvement in the HT Cable tangent delta value. The transformer was Energised and put back into service. A post rectification PD scan was done and found that the PD had been cleared.
PD activity on Ultrasonic PD mode (After)
The Partial Discharge abnormality was detected and resolved within 24hours, reflecting our dedication and capabilities to provide technical and engineering support for our clients.
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