The use of natural ester liquids in power transformers, as an alternative to mineral oils, is increasing in the last decades due to the higher interest in reducing the environmental and fire risks. This is possible thanks to the fact that natural ester liquids present much higher flash fire points and biodegradability, also satisfying the general principles of a circular economy.
The IEC 61294 Technical Report, published in 1993, describes a simple test procedure to measure the PD Inception Voltage (PDIV) in insulating liquids and doesn't cover any other items related to the PD patterns and their evolution at higher voltages.
Partial Discharges (PD) detection in HV components has shown to be a very powerful diagnostic tool. Anyway, also the acquisition of the same signals in simple insulations, like the dielectric liquids, may give additional information for maintenance of HV components in which they are employed, as in the case of liquid insulated transformers.
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