Research On Test Method Of Multiple Frequency Dielectric Response On Oil-Paper Insulation

Power transformers play a key role in the process of transmission and distribution, its good running condition is the key to ensure the safety of power grid, however, the key factors to ensure transformers’normal running is its oil-paper insulation system. Testing the oil-paper insulation system of transformer at regular intervals and evaluating the aging condition and moisture content are the key premises for the maintenance of transformers, they also play a very important significance to ensure the safe and stable operation of transformers, to ensure the safe and economical operation of power grid.Frequency domain dielectric spectroscopy (FDS) is one of the nondestructive method to diagnose the state of insulation of transformers, which essence is to measure the polarizing response of insulation under the excitation of alternating electric field, usually by changing the excitation frequency point and scanning measurement. FDS has the advantages as the small noise, low testing voltage required, and rich information carried. Cause of the low testing frequency and single oscillation, traditional measuring method of FDS consumes a lot of measuring time. In actual working condition, the window time is short, time is very limited for transformer testing, and influenced by environmental temperature, internal temperature of the transformer is variable in the process of actual measurement, too long testing time will affect the effectiveness of test result. Therefore, the traditional method of FDS may not apply.Based on the above reasons, this paper proposes a more efficient solution to save time, which is Multiple frequency domain dielectric spectroscopy (MFDS) test method. Basic principle of this method is through the measurement of multiple sinusoidal oscillation at the same time to reduce the measuring time. Specifically, MFDS test method is to act on the insulating medium with multiple frequency signal composed of several sinusoidal voltage excitation, to replace the traditional single sinusoidal voltage excitation. Fit the obtained mixing current response curve, and disassemble it with the super-resolution method based on compressed sensing, finally get the response information corresponding to every single sinusoidal voltage signal. Then the judgment factors if oil-paper insulation such as complex capacitance and dielectric loss angle tangent can be obtained through calculation. This article compared complex capacity curve measured by MFDS with which measured by traditional FDS and IDAX300 insulation diagnosis analyzer, MFDS method is proved feasible and reliable. This paper, by using MFDS method, tested the oil-paper insulation sample under different conditions such as different temperature, different aging levels, different moisture content, and got the dielectric response curve. During further experiments the author found to meet the minimization of time cost, the full mixing signal cycle is not necessary during the practical measuring, only part of the cycle was required, it can get good results as well through the mathematical fitting.The research results show that to get the same amount of frequency information, the MFDS method measured once which the traditional FDS method measured several times. Through comprehensive consideration, MFDS method can save a lot of measuring time. No matter from the point of view of the sources of energy, the economy and the manpower resource, the MFDS method achieved the desired effect of high efficiency, energy saving, and time saving.