Investigation of FRA for Transformer by using the Square Wave Voltage

The frequency response analysis (FRA) of transformer has been expected to be a good method for diagnosing the transformer condition. The special measuring instrument is usually used for the FRA measurement. So, in this paper, a new method of FRA measurement using a general-purpose square wave source and the oscilloscope is proposed. FRA of this method is evaluated with the frequency response characteristic of the transformer input impedance. The procedures of this method are as follows. First, the square wave voltage is applied to a transformer and the input voltage and the input current at that time are measured with the oscilloscope. Next, the high order frequency components of voltage and current are calculated by Fourier series expansion. At last, high order transformer input impedance is calculated by doing division of the high order frequency component of the input voltage and the input current. Frequency response characteristics of the input impedance of the transformer are provided in the above-mentioned procedure. As the experiment that applied this method to a pole transformer was a good result, we report it.