The characteristics of FRA results for different tap position on inter bus transformer (IBT) 166 MVA

Nowadays, Sweep FRA becomes a common measurement tool used to identify the transformer condition. The standard for this technique and how to interpret the result has been released by CIGRE and IEEE. PT PLN P3BJB is operating 787 transformers from various voltage ratios. Most of the transformers are 150/20 kV (64.4%) and there are 35 transformers operated in 500/150 kV. Each of the transformers is provided with OLTC to adjust the output voltage. As a common knowledge, every transformer has its own RLC value. The RLC value will be influenced by some factors, i.e. natural aging, low voltage side disturbance or even tap position. If the tap position changing, the number of turn will be different, means RLC value will be different. Based on this condition, interpretation should be done carefully. In this paper we will describe the characteristic of SFRA measurement result for Inter Bus Transformer (IBT) 166 MVA operated in 500/150 kV. According to measurement results, by changing the tap position, the pattern of SFRA result for IBT 166 MVA will be different in frequency range 1 kHz-100 kHz, especially for full tap winding and without tap winding.