This project deals with the electrostatic charging tendency (ECT) at oil/pressboard interfaces of forced cooled high-voltage power transformers. There are three main methods for screening the ECT of liquid/solid insulating components. Duct or pipe models relate to a plane and uniform oil flow, other test set-ups are based on a rotating oil flow or on filter methods. Due to the complex interfacial phenomena at the liquid/solid interface there are no single method or device which can fulfil all the required specifications for ECT-evaluation. Medium or large-sized duct or pipe models of rectangular or circular cross section are most suitable regarding uniform laminar or turbulent flow conditions. The main disadvantage of these methods relates to the high volume of the samples and to the amount for pre-processing and conditioning the liquid and solid components. ECT-evaluation with the so-called Cigre Test Cell (CTC) mitigates some of these problems. Nevertheless, the CTC-method is not suitable for a standardised quick and on-site evaluation of ECT. One of the essential problems of standardised ECT-evaluation is the moisture transfer. There are a lot of difficulties in achieving a steady-state moisture condition even after careful pre-processing. Therefore at present the Ministatic Test (MST) is most suitable for standardisation and for on-site ECT-evaluation even though measured ECT-index (charge/volume) is not comparable directly with th...(this text has been cut automatically)
|Effective start/end date||1/01/95 → 31/01/01|
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