Transformer fault discrimination and protection method

Abstract

The invention provides a transformer fault discrimination and protection method. The three-phase power average Pavr of a transformer two-terminal network and the waveform chart of the three-phase power average Pavr are calculated and obtained. According to the waveform chart of the three-phase power average Pavr, the frequency F of the waveform chart of the three-phase power average Pavr is calculated, whether at least two phases of frequencies F close to 50Hz exist or not is judged, if so, transformer rush current is judged, if not, a transformer internal fault is judged, and a corresponding protection action is executed according to a judgment result. According to the method, starting from instantaneous power waveform characteristics, effective information is mined, a fast, simple, reliable and novel transformer protection method is provided, the amount of calculation is small, the setting is convenient, the method is not affected by a Y / Delta wiring side formula, the know of the leakage inductance parameter of a transformer is not needed, and compared with existing power differential method and an existing differential protection method, the method has the significant advantages of better rapidity, sensitivity and reliability.

Description

technical field [0001] The invention relates to a transformer fault identification and protection method, in particular to a transformer fault identification and protection method based on generalized instantaneous power waveform characteristics applied to large transformers in ultra-high voltage power grids. Background technique [0002] As one of the core components of UHV and EHV systems, large transformers put forward higher requirements on the quickness and reliability of their digital protection. However, the correct action rate of transformer protection has been low for a long time, and the transformer differential protection itself has defects in principle. The key to correct action is still to distinguish between excitation inrush current and internal fault current. The traditional excitation inrush current identification methods, such as the second harmonic braking principle, the discontinuous angle principle, etc., all use a single current information as the basis...

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Problems solved by technology

[0005] 2) The capacitive current generated by the distributed capacitance in the UHV system is relatively large, which will affect the reliability and sensitivity of the differential protection

In transient processes such as transformer no-load closing, external fault removal, and reclosing, it is affected by the parallel reactance in the system (J.FaizandS.Lotfi-Fard. A new wavelet transform-based excitation inrush current and internal power transformer Fault identification algorithm[J].IEEETrans.PowerDelivery,2006,21(4):1989-1996.), the current is easily distorted, and the current phase on both sides of the transformer has a large deviation, which brings serious damage to the differential protection. influences

At the same time, the distributed capacitance causes a high frequency component in the transient current, and the unbalanced current of the fault outside the area is very large, which is more likely to cause misoperation of the differential protection

[0006] 3) For the protection of UHV large transformers, due to the improvement of iron core material and the change of transformer structure, its excitation characteristics are more complicated, and more perfect protection schemes need to be studied

At the same time, when the UHV system fails, the high-order harmonic components in the fault current increase, which makes the transformer protection based on the harmonic braking principle delay the action time of the protection when the internal fault occurs, affecting the rapidity of the protection action (X .Lin, Jin.Huang, et al. Electromagnetic transient analysis and adaptability of UHV power transformer differential protection principle based on second harmonic braking principle[J].IEEETrans.onPowerDelivery,2010,25(4):2299 -2307.)

[0007] 4) Due to the influence of series compensation capacitor and parallel compensation reactance in UHV system, its non-periodic component attenuation is very slow and the existence of non-integral harmonic content, the digital filter algorithm for large transformer protection, especially the short window digital filter algorithm It has a great impact, which further affects the action speed of the protection

[0028] On the other hand, for the calculation of active power, there have always been many controversies in the theoretical circles, because the traditional power theory is based on the average value, which is only applicable to the sinusoidal steady state, and whether the transformer is short-circuited or in a state of In the excitation inrush current state, there is a transition transient process. When the voltage and current contain harmonics, the power phenomenon is more complicated, and the traditional power theory cannot explain and describe it reasonably (in sinusoidal, non-sinusoidal, balanced IEEE Trial Standard for the Definition of Measurement of Electric Power Values ​​under Unbalanced and Unbalanced Conditions, IEEE Std.1459-2010, February 2010.)

[0029] Therefore, none of the above solutions can well solve the problem of sensitivity and rapidity of large transformer protection in the UHV power grid.

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