PD Cases

PMDT has collected many case studies from conducting testing jobs for clients throughout the years. Below are a few examples of these case studies.

Case Study 1

In the following case study, the PDetector and PDExpert were used to detect and locate a PD signal source on a 110kV Switchgear. During the routine PDetector, the UHF sensor along with spectrum analysis method was used to analyze the detected signals.

The UHF PRPD-PRPS spectrum has two clusters large amplitude clusters of pulses at 90 degrees and 270 degrees, separated by 180 degrees. These characteristics indicate there is PD within the Switchgear and the type is Floating Electrode.

After TDOA method testing with the PDExpert, it was determined that the PD signal source location is at the yellow circle in the picture below.

Case Study 2

In this case study, the PDetector was used to detect and locate a PD signal source inside a 500kV GIS Circuit Breaker. During the routine PDetector, the UHF sensor, along with spectrum analysis method, was used to analyze the detected signals.

Using the AE Contact probe on the elbow compartment, an abnormal signal was detected. From the AE Waveform below (bottom left), PD activity was determined. AE magnitude location technology was used to find the PD source location my moving the AE Contact probe around the enclosure and comparing the signal magnitude. The largest magnitude was detected at the bottom of the enclosure. The AE Fly Spectrum (bottom right) shows the PD signals had a distinct pattern and characteristics that indicate the PD type to be Particle Discharge.

The GIS was deenergized and maintained. The particle was found at the bottom of the enclosure.

Case Study 3

In this case study, the PDetector and PDExpert were used to detect and locate a PD signal source coming from a Transformer. During the routine PDetector, the HFCT sensor, along with spectrum analysis method, was used to analyze the detected signals.

Using the HFCT sensor on the grounded strap, an abnormal signal was detected. From the PRPD/PRPS spectrums, PD activity was determined to be Floating Electrode.

The Transformer was deenergized to find the PD issue. Floating electrode discharge was found from the accessory of the bushing. Physical PD tracking was also found. Later, maintenance was performed for the bushing. PDetector was used to test the Transformer after the maintenance when the Transformer was energized again. AE and HFCT methods did not find any abnormal signals. The issue was resolved successfully. 

Damage Cause by PD Activity

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