Various partial discharge (PD) measurement techniques have been developed recently, mainly for on-site and online measurements. These measurements aim to “improve the reliability of the power system and that insulation faults can be discovered in time to avoid uncontrolled power system failures.”
For utilities, the most interesting feature of online measurements is that electrical service is not interrupted once the sensors are installed in the network. Therefore, we will focus on online measurement tests applying a sophisticated measurement procedure to counter the abovementioned challenges.
Two approaches to on-site PD testing on high voltage (HV) networks exist: scheduled online testing and continuous online monitoring. Ampacimon has performed several online PD tests to determine the insulation status of various HV equipment in the following way:
- The measurements were performed with a measuring instrument consisting of a digitiser with 14-bit vertical resolution, 50 MHz bandwidth and 100 Ms/s sampling rate so that the signal data is acquired utilising broadband measurements, which allows digitising the transient PD signals associated with degradation phenomena.
- A powerful wavelet transform based filtering technique is implemented in the measurement unit to distinguish between pulse-like signals generated by PD sources and background noise.
- In addition, the processing software includes two pulse classification tools to locate and distinguish between different pulse sources present in a test object. The first one is based on the analysis of the delay between the arrival times of the pulses at the sensors placed at a known distance in the test object (pulse localisation classification). The second classification tool is based on the analysis of the waveform of the recorded pulses (classification by pulse shape).
In this way, Ampacimon BlueBOX technology can automatically acquire online measurements of PD so that it is easy to extract the relevant pulses for identifying degrading insulation conditions and its position. With precise information about the location and severity of insulation degradation, the cable owner can efficiently attend to maintenance before it completely breaks down.
Image source: Courtesy of Ampacimon
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