Water turbine tail water pipe dynamic characteristic extraction method

Abstract

The invention relates to a water turbine tail water pipe dynamic characteristic extraction method. The method comprises the following steps that pressure fluctuation signals of a water turbine tail water pipe under three states of no vortex strip, vortex strips and serious vortex strips are collected by a field test which is carried out by a hydroelectric generating set; the collected pressure fluctuation signals are subjected to resample under the three states of the water turbine tail water pipe, and high-frequency interference in the pressure fluctuation signals is removed; the pressure fluctuation signals subjected to resample under the three states are resolved by adopting an intrinsic time-scale decomposition method, and a monotonous baseline vector and a plurality of intrinsic rotational components are obtained corresponding to the pressure fluctuation signals under the three states; the dynamic characteristics of the water turbine tail water pipe are extracted by the approximate entropy of the intrinsic rotational components, which is respectively obtained by calculation, of the water turbine tail water pipe under the three states. The water turbine tail water pipe dynamic characteristic extraction method has the advantages of efficiency, strong instantaneity and the like, and can be widely applied to the fields of running guarantee of the hydroelectric generating set.

Description

technical field [0001] The invention relates to the technical field of on-line monitoring and state evaluation, in particular to a method for extracting dynamic characteristics of a water turbine draft tube. Background technique [0002] With the continuous increase of the unit capacity and size of hydroelectric units, the operating status of hydroelectric units has a greater impact on hydropower plants and their interconnected grids. Large-scale hydroelectric units mostly use Francis turbines with fixed runner blades. When the hydroelectric units operate under partial load conditions, the turbines cannot meet the optimal flow conditions at the runner inlet and outlet at the same time, and unstable eccentricity will be formed in the draft tube. The vortex belt will lead to cracks and cracks in the runner and draft tube, and will break in severe cases. At the same time, it will cause the instability of the vibration of the shafting of the hydroelectric unit, threatening the s...

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Problems solved by technology

Although the EMD method can adaptively analyze the signal according to the characteristics of the signal itself, there are still limitations in theory such as frequency confusion, over-envelope, under-envelope, endpoint effects, and negative frequency components with no physical meaning.

Moreover, when the EMD method is used to decompose the signal, it must be iterated many times in the screening process to decompose the IMF, and each iteration needs to search for extreme points, calculate the cubic cloud coefficient and find out the upper and lower envelopes, so that resulting in inefficient decomposition of

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