Frequency domain dielectric spectroscopy（FDS）

a diagnostic method to diagnose the insulation condition of transformers

needs to scan the excitation frequency point-by-point in the general condition

which takes a long period in the low frequency. So it may not be appropriate in some time-limited conditions. To solve this issue

we put forward a testing method of FDS affected by hybrid frequency voltage. The proposed method imposes a composite hybrid-frequency signal to the dielectric as input stimulus. The current response information is decomposed into several sinusoidal waves which match the corresponding frequency

then the complex capacitance can be acquired through calculation. The oil clearance experimental results reveal that a contrast of the decomposition value of the hybrid frequency response and the value of single frequency response between the two methods shows the correctness of the proposed FDS. Meanwhile

this method is adopted to measure the dielectric spectrum of oil-paper insulation and real transformer and compared with the scanning frequency results of IDAX300. The results show that the proposed method almost coincides with the conventional FDS method in complex capacitance

while the proposed method can remarkably save time.