217 / 2022-03-14 19:31:04

Method for the determination of correct calibration pulses in PEA measurements

space charge measurement,pulsed electro-acoustic(PEA) method,Space charge densities

Purpose/Aim

The Pulsed Electro-Acoustic (PEA) method is being increasingly adopted by institutions and industries in the development of dielectrics for HVDC applications. A correct PEA measurement always requires postprocessing of raw data coming from the experimental setup (the so-called calibration of the signal). One fundamental step required to correctly calibrate the PEA signal is the identification of a time instant at which no space charge is being accumulated in the specimen. This can be done in different ways, with different levels of reliability. This work proposes an alternative method, which minimizes the possibility of an incorrect evaluation regarding space charge accumulation at the very beginning of polarization in a material.

Experimental/Modeling methods

Experimental setup is based on the introduction of a floating mass in the thickness of the material to be tested. This might be done fusing multiple layers of insulating materials together, and embedding a floating electrode. Probing of the potential of the metallic interfacial electrode can be done both when the specimen is under an AC supply, and also in DC, during polarization and depolarization phases. The evolution of the detected potential over time, when no space charge is being injected, must be proportional to the potential applied to the test sample, as the system acts as a voltage divider. Discrepancies of such proportionality factor over time should indicate that space charge accumulation is being injected in the specimen.

Results/discussion

Tests were run poling specimens both in AC and in DC. Analysing the time evolution of the proportionality factor between the applied voltage and the floating mass potential, there is clear indication that an amount of space charge is being injected, in DC, after a certain time, depending on the kind of insulation and testing conditions. Hence, the calibration pulse should be chosen from acquisitions within such time.

Conclusions

The calibration process of PEA measurements is prone to uncertainties, since a signal supposedly free of charge accumulation should be selected. The proposed method is a viable option to ensure that is indeed the case, with much less uncertainties than more traditional methods.