On-line Detection of GIS and Tank-type Circuit Breaker PD Defects

Manifestations of GIS Insulation Breakdown 

At the Initial Stage: The insulation breakdown is mostly caused by metal particles, floating conductor, surface burr or particles. Improvement of handover test can have a preventive effect.    

At the Middle stage: Most of insulation breakdowns is caused by defects on the insulator surface (such as pollutant, charge accumulation and attached metal particles ). Regular inspection can find these hidden troubles.

The IEC specifies that when the GIS is delivered, the PD level should be less than 5pC and less than 10pC for on-site handover and operation.  

Traditional technique: cannot solve the anti-interference problem; difficult to reach the necessary detection sensitivity; usually used in lab. UHF technique: detect ultra-high frequency electromagnetic signals; broad detection range and free from corona interference in the air. Sensitive to all defects, reaching pC. AE technique: detect ultrasonic signals and resistant to electric interference; very sensitive to free particle defects and metal part vibration; reach pC values when close to defective part. Gas analysis technique: It takes some time for decomposition to generate and diffuse. Hence, the response speed is slow and the sensitivity is low.