Research Papers: Fundamental Issues and Canonical Flows

Stability Limits of Reversible-Pump Turbines in Turbine Mode of Operation and Measurements of Unstable Characteristics

[+] Author and Article Information
Grunde Olimstad

 Department of Energy and Process Engineering, NTNU University in Trondheim, Alfred Getz vei 4, Trondheim, 7491, Norwaygrunde.olimstad@ntnu.no

Torbjørn Nielsen

 Department of Energy and Process Engineering, NTNU University in Trondheim, Alfred Getz vei 4, Trondheim, 7491, Norwaytorbjorn.nielsen@ntnu.no

Bjarne Børresen

 Energi Norge, Næringslivets Hus, Middelthunsgate 27, Oslo, Norwaybbo@energinorge.no

J. Fluids Eng 134(11), 111202 (Oct 23, 2012) (8 pages) doi:10.1115/1.4007589 History: Received April 12, 2012; Revised September 01, 2012; Published October 23, 2012

Measurements have been performed on a reversible-pump turbine model installed in a closed loop conduit system. The characteristics of the unstable pump turbine in turbine mode show a hysteresis pattern. Hence the output of the system is dependent on the previous state of the flow and not only the input variables. The hysteresis pattern is a characteristic of the whole system, but is caused by the unstable pump turbine. The unstable part of the characteristics was measured by three different methods: 1) by transient sampling of data during the transition between operation modes, 2) by throttling valves that steepens the friction-loss curve, and 3) by switching the causality in the system such that the torque becomes an input parameter and the speed of rotation becomes an output parameter. In the valve throttling measurements a pressure dependency was seen for the characteristics at high nondimensional speeds. This was further investigated by additional measurements of the characteristics at three different pressure levels. A rigid-water-column stability analysis has been conducted. The classic H-Q criterion describes static stability for a pump turbine with constant speed of rotation. With the speed of rotation as a variable, there is a new static stability criterion in addition to the dynamic stability criterion.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Simple power plant system with indicated upper and lower reservoir, water conduits, and turbine

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Figure 5

Meridional view of the runner blade surface

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Figure 6

Performance diagram with labeled efficiency contours

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Figure 7

Hysteresis flow-speed curves with 10 deg guide vane opening

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Figure 8

Hysteresis Qed -Ned characteristics with 10 deg guide vane opening

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Figure 9

Inputs to and outputs from the system

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Figure 10

Transient measured characteristics for three different guide vane openings (α)

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Figure 11

Stabilizing through valve throttling

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Figure 12

Characteristic with torque as input

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Figure 13

Standard deviations in the unstable zone

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Figure 14

Comparison of the three measurement techniques

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Figure 15

Final Qed -Ned characteristics

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Figure 16

Final Ted -Ned characteristics

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Figure 17

Pressure dependent characteristics

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Figure 18

Marker sizes correspond to plus/minus three standard deviations

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Figure 2

Limiting lines for the slope of the characteristics in turbine mode

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Figure 4

Radial view of the runner blade surface




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