Research On Novel Principles And Algorithms Of Power Transformer Main Protection

In the power system, it is of great theoretical significance and high practical value to develop a new transformer protection principle with higher reliability and better performance. This paper makes a study on the transformer protection from two aspects,'new ideas'and'old problem'. A new principle based on the equivalent resistance is proposed. Using the theory of instantaneous power, the port equivalent resistance is defined to reveal the difference between the internal and external fault, not subject to the impact of the inrush current, non-periodic component, the transformer leakage impedance, intermittent angle. The new principle is very different with the differential protection. For the limitation of the existing time difference, the paper also proposes a new principle based on an improved time difference, which uses the wavelet transform to extract high- frequency details and singular point information. This paper introduces the spectral entropy into the transformer protection, using the physical meaning of entropy to reflect the inrush information in a cycle and constitute a criterion. This paper uses the two-instantaneous-value-product algorithm to extract the fundamental amplitude of current, and uses two factors (the time of reaching the maximum and the ratio of the first local maximum and the maximum) to constitute a criterion of the transformer protection. The new criterions of the transformer protection have been verified by a lot of dynamic experiments, which show the effectiveness of the methods.