Application of Finite Element Methods for Accurate Derating of Distribution Transformers under Simultaneous Non-sinusoidal Supply Voltages and Nonlinear Loads

摘要

In this paper, the well known formula which is commonly used to derate distribution transformers is modified for precise derating distribution transformers under nonlinear conditions. Hence, a novel technique is proposed to calculate equivalent kVA for different operational cases of transformer. Derating of distribution transformers under simultaneous nonlinear loads and non-sinusoidal supply voltages are investigated in details: Against previous published methods which ignored core losses during their investigations, copper losses, eddy current losses and iron core losses are calculated and taken into account. In this process, the distribution transformer under above mentioned conditions is modeled using time stepping finite element method to precisely account the geometry and physical characteristics of different segments of the transformer. Magnetic flux density, time variation and frequency spectra of the terminal voltages, output power, copper losses, winding eddy current losses and iron core losses are evaluated in different conditions. The determined equivalent kVA of transformer for the aforementioned operations using TSFEM is compared with IEEE standards and their differences are justified incisively. Simulation results are verified by experimental results.