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Measurement of the No-Load Characteristics of Single-Phase Transformer Using an Improved Low-Frequency Method

A large-capacity nominal-frequency (NF) power supply is required to measure the no-load characteristics of transformers, including the no-load loss, excitation current, and no-load current harmonic content for field and factory tests. The traditional NF method uses bulky test equipment and requires a highly complex test operation. This paper proposes an improved low-frequency (LF) method to reduce the capacity requirement of the testing power supply and make the test equipment portable. In this method, the core loss at LFs is first calculated by applying sinusoidal voltages at several LFs. The resultant core loss at LFs is then converted to core loss at NF based on the core loss separation and orthogonal least squares method. Finally, the excitation current, no-load loss and excitation voltage are determined by a corresponding eddy current compensation algorithm. In addition, experiments were conducted on a single-phase distribution transformer. The experimental results confirm that, compared to the traditional NF test, the proposed method possesses a similar measuring accuracy but reduces the capacity requirement of the testing power supply.