Abstract
The low frequency section of frequency domain spectroscopy (FDS) of oil-paper insu- lation system can effectively reflect the ageing state and moisture of the oil-immersed paper. Meanwhile, steady-state insulation resistance is the one of indexes for the condition of transformer. In actual measurement, these two both are time-consuming and poor accessibility, thereby restraining their field applications. Aim at this problem, this paper analyses the polarization process of the oil-paper insulation in transformer, and adopts a low frequency equivalent circuit model for the oil-paper insulation to characterize the polarization process at low frequency. The simulated annealing particle swarm optimization (SAPSO) algorithm is proposed to identify the parameters in equivalent circuit, which are affected by change of insulation state. Compared with the experimental results, the errors of the steady-state insulation resistance and the tan $\delta $ below 10−3 Hz, which are calculated by the identified parameters, are less than 2.5%. This method can avoid the influence from external environment and reduce the measurement time. The time and frequency domain parameters calculated can provide reference for the ageing assessment of oil-immersed paper.
Highlights
Oil immersed power transformer is one of the most widely used equipment in power system
To characterize the interfacial polarization, the Maxwell model is used into the equivalent circuit of oil-paper insulation, shown in the Fig 3, where the conductance loss is caused by the resistance existing in the circuit, and the parallel structure of two dielectrics can reflect the interfacial polarization process
Due to the initial derivative of recovery voltage and the recovery voltage correspond with the insulation sate of transformer, the previous researches focused on modeling the dielectric response of transformer insulation with recovery voltage method (RVM) [14]–[16]
Summary
Oil immersed power transformer is one of the most widely used equipment in power system. To characterize the interfacial polarization, the Maxwell model is used into the equivalent circuit of oil-paper insulation, shown, where the conductance loss is caused by the resistance existing in the circuit, and the parallel structure of two dielectrics can reflect the interfacial polarization process. Due to the initial derivative of recovery voltage and the recovery voltage correspond with the insulation sate of transformer, the previous researches focused on modeling the dielectric response of transformer insulation with RVM [14]–[16] They can be both used to identify the parameters of the equivalent circuit, the laplace transform of recovery voltage is so difficulty to deduce that it leads to enormous calculation when the number of branches is increased [14]. R(tj) where R(tj) represents the measured value of insulation resistance in charge time of tj
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