M. Soltanmohammadi - Zangan Distribution Transformer Co.,Zanjan ,Iran.
A. Eslamian - Instructor, Zanjan Branch, Islamic Azad University, Zanjan, Iran.

Cast resin transformers are the most attractive type of distribution transformers. These types of transformers are installed near residential areas since they are clean and safe. Restricting the noise level in a standard limit is very important biologically.According to the literature the geometry of the core and magnetostrictions caused by the magnetic fields are the most two important sources of noise generation in transformers. To evaluate the effective parameters on the overall mean sound level of transformers a large number of fabricated CRT transformers in Irantransfo Co. are tested and simulated. Noise Level of each sample is measured according to IEC60651 criteria. Numerical simulations are done using ANSYS software. Pearson factor showed that there is a robust conjunction between first natural frequency and noise level of CRTs. Considering some simplifications and assumptions a novel two-condition equation is extracted for approximating mean noise level of the transformers prior to fabrication in design phase. This correlation between the numerical and experimental values is proposed in such a way that knowing dimensions of the core of the transformer and first natural frequency of the core, approximate value of the mean noise level could be forecasted. Finally the proposed semi-practical equation is implemented for 8 other cases as the witness ones to check the repeatability and precision of the so called equation. Comparison of the results with experimental values showed that the proposed equation could be used to approximate mean noise level in design phase prior to manufacturing with ±10% mean tolerance.

Semi-practical Relation, Optimized-Noise, CRT Transformers, FEM