Dynamic instability of a pump-turbine in load rejection transient process

Hysteresis effect, which has a significant impact on transient characteristics of a pump-turbine, attracts more and more researchers’ attention and shows great potential. Influences of hysteresis on dynamic characteristics of a pump-turbine are investigated during the transient process in this paper. Transient trajectories of pump-turbines actually do not match their static operation trajectories, especially in the condition of turbine braking. In order to establish a transient model of a pump-turbine in different moving directions of dynamic trajectories, time delays among the relative parameters are introduced in this paper. Furthermore, effects of hysteresis on the dynamic characteristics of the pump-turbine are analyzed in detail by using numerical simulation. Based on the established transient model, influences of unit head on the dynamic characteristics of the pump-turbine are studied during the bidirectional transient process. The simulation results show the transient characteristic of the pump-turbine can be improved with the enhancement of hysteresis effect. While it gradually loses stability with the increase of hysteresis. The conclusions provide us a new approach for regulating the transient performance and stability of pump-turbines by using hysteresis effect during transient process.

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Hydraulic fluctuations during the pump power-off runaway transient process of a pump turbine with consideration of cavitation effects

Journal of Hydrodynamics ◽

10.1007/s42241-022-0105-5 ◽

2021 ◽

Vol 33 (6) ◽

pp. 1162-1175

Author(s):

Xiao-long Fu ◽

De-you Li ◽

Hong-jie Wang ◽

Yong-guang Cheng ◽

Xian-zhu Wei

Keyword(s):

Pump Power ◽

Transient Process ◽

Pump Turbine

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Transient Process inversion calculation and extreme condition prediction of large pump turbine based on field test

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/304/2/022019 ◽

2019 ◽

Vol 304 ◽

pp. 022019

Author(s):

Gaohui Li ◽

Tianchi Zhou ◽

Xuesong Yu ◽

Minjie Yao

Keyword(s):

Transient Process ◽

Field Test ◽

Extreme Condition ◽

Pump Turbine ◽

Inversion Calculation

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Analysis of the Mechanism of Microtubule Dynamic Instability Using a UV Microbeam to Sever Elongating Microtubules

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100102699 ◽

1988 ◽

Vol 46 ◽

pp. 122-123

Author(s):

R.A Walker ◽

S. Inoue ◽

E.D. Salmon

Keyword(s):

Dynamic Instability ◽

Microtubule Dynamic ◽

Gtp Hydrolysis ◽

Abrupt Transition ◽

Microtubule Associated Proteins ◽

Asymmetrical Structure ◽

Associated Proteins

Microtubules polymerized in vitro from tubulin purified free of microtubule-associated proteins exhibit dynamic instability (1,2,3). Free microtubule ends exist in persistent phases of elongation or rapid shortening with infrequent, but, abrupt transitions between these phases. The abrupt transition from elongation to rapid shortening is termed catastrophe and the abrupt transition from rapid shortening to elongation is termed rescue. A microtubule is an asymmetrical structure. The plus end grows faster than the minus end. The frequency of catastrophe of the plus end is somewhat greater than the minus end, while the frequency of rescue of the plus end in much lower than for the minus end (4).The mechanism of catastrophe is controversial, but for both the plus and minus microtubule ends, catastrophe is thought to be dependent on GTP hydrolysis. Microtubule elongation occurs by the association of tubulin-GTP subunits to the growing end. Sometime after incorporation into an elongating microtubule end, the GTP is hydrolyzed to GDP, yielding a core of tubulin-GDP capped by tubulin-GTP (“GTP-cap”).

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Time-Resolved Cryo-Electron Microscopy of Oscillating Microtubules

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100181269 ◽

1990 ◽

Vol 48 (1) ◽

pp. 502-503

Author(s):

Eva-Maria Mandelkow ◽

Ron Milligan

Keyword(s):

Electron Microscopy ◽

Dynamic Instability ◽

Entire Solution ◽

Reaction Scheme ◽

Time Resolved ◽

X Ray ◽

X Ray Scattering ◽

A Chain ◽

Ray Scattering

Microtubules form part of the cytoskeleton of eukaryotic cells. They are hollow libers of about 25 nm diameter made up of 13 protofilaments, each of which consists of a chain of heterodimers of α-and β-tubulin. Microtubules can be assembled in vitro at 37°C in the presence of GTP which is hydrolyzed during the reaction, and they are disassembled at 4°C. In contrast to most other polymers microtubules show the behavior of “dynamic instability”, i.e. they can switch between phases of growth and phases of shrinkage, even at an overall steady state [1]. In certain conditions an entire solution can be synchronized, leading to autonomous oscillations in the degree of assembly which can be observed by X-ray scattering (Fig. 1), light scattering, or electron microscopy [2-5]. In addition such solutions are capable of generating spontaneous spatial patterns [6].In an earlier study we have analyzed the structure of microtubules and their cold-induced disassembly by cryo-EM [7]. One result was that disassembly takes place by loss of protofilament fragments (tubulin oligomers) which fray apart at the microtubule ends. We also looked at microtubule oscillations by time-resolved X-ray scattering and proposed a reaction scheme [4] which involves a cyclic interconversion of tubulin, microtubules, and oligomers (Fig. 2). The present study was undertaken to answer two questions: (a) What is the nature of the oscillations as seen by time-resolved cryo-EM? (b) Do microtubules disassemble by fraying protofilament fragments during oscillations at 37°C?

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