The necessary state of performance that should be compulsory in the international regulations for testing noise of power transformers

In recent years, more and more transformers are designed with low induction levels and improved core designs. That leads to a change in the contribution hierarchy of the sound sources in transformers. According to the IEC Power transformer standard, the decision as to whether it is significant to perform load current sound measurements is made on a single equation which depends only on the rated power. In this paper we shall suggest, through test examples, that this equation can be misleading and a modified methodology which is based on measurements of noise at both “no-load” and “load” states, is necessary.