On the one hand, reference signals are important parts of the method proposed in this paper. They are used to compare with test signals to assess the condition of OLTCs. On the other hand, repeatability is an important factor for the extracted characteristic parameter. A good characteristic parameter can reflect the essential features of a vibration signal and it must possess excellent repeatability. In order to test the repeatability of the parameter proposed in this paper, the first 10 vibration signals from an OLTC in good condition are chosen. One of them is treated as the reference signal. D between the reference signal and the other nine signals is calculated, and the results are shown in Table II. All results are in the following. It means that the parameter matrices of vibration