Examination of the Recovery Voltage Measurement's evaluation

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Supervisor:
Dr. Németh Bálint
Department of Electric Power Engineering

As electricity appeared in all part of life, the importance of service’s reliability increases. As temporarily electricity can not be stored in eligible quantities, it must be generated constantly depending on the consumer demand. It is only possible with equipments which are reliable, fail-safes. The most valued element of the electrical transmission system is the transformer. These equipments’ lifetime is principally determined by the condition of the insulation system. Mostly the transformers’ oil-paper insulation will be introduced in my work

A lot of destructing effects can act on operating devices. These impressions may amplify each other and irreversibly worsen the insulations’ physical, chemical and electric properties. The devices’ lifetime can be lengthened by the proper maintenance, renewal or change of equipments. For that we must know the condition of the insulation. There are many diagnostic methods available for monitoring insulation systems. During my work I was fully concerned with the Recovery Voltage Measurement (RVM) method and its evaluation. This technique was evolved by Budapest University of Technology and Economics and nowadays it is used expansively for monitoring of transformers’ oil-paper insulation. There are some parameters which define relation between RVM curves and the measuring temperature. Towards more accurate evaluating of RVM results, I tried to determine these coefficients by elaborating former RVM outcomes. With further examination, we would be able to create an evaluating method which takes the equipments’ age into consideration. The final aim is to make a computer-aided evaluation system which determines the insulation system’s condition as precisely as possible, by using the outcomes of RVM and other diagnostic methods.

In the first part of my thesis I would like to introduce the features of the transformers’ oil-paper insulations. After that I resume with the review of RVM method, including theoretical basics and principal attributions. In the fourth chapter I show the RVM results which were measured during the development of the technique. I introduce the process chosen by me for evaluating the mentioned former results. Furthermore I discuss the examination of aging effect. In the end I analyse the practical utilities of the acquired experiences. The task is to supplement the current RVM evaluation, suggested by standard (MSZ 19323:2002), so we will be able to rate the insulation’s condition as accurately as possible.

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