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Research Papers: Flows in Complex Systems

Transient Pressure Measurements on a High Head Model Francis Turbine During Emergency Shutdown, Total Load Rejection, and Runaway

[+] Author and Article Information
Chirag Trivedi

Indian Institute of Technology Roorkee,
Roorkee, Uttarakhand 247667, India;
Luleå University of Technology,
Luleå SE-971 87, Sweden
e-mail: Chirag.Trivedi@ltu.se

Michel J. Cervantes

Professor
Luleå University of Technology,
Luleå SE-971 87, Sweden;
Norwegian University of Science and Technology,
Trondheim 7491, Norway
e-mail: Michel.Cervantes@ltu.se

B. K. Gandhi

Mem. ASME
Professor
Indian Institute of Technology Roorkee,
Roorkee, Uttarakhand 247667, India
e-mail: bkgmefme@iitr.ernet.in

Ole G. Dahlhaug

Professor
Norwegian University of Science
and Technology,
Trondheim 7491, Norway
e-mail: ole.g.dahlhaug@ntnu.no

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 23, 2013; final manuscript received May 27, 2014; published online September 10, 2014. Assoc. Editor: Bart van Esch.

J. Fluids Eng 136(12), 121107 (Sep 10, 2014) (18 pages) Paper No: FE-13-1633; doi: 10.1115/1.4027794 History: Received October 23, 2013; Revised May 27, 2014

The penetration of intermittent wind and solar power to the grid network above manageable limits disrupts electrical power grids. Consequently, hydraulic turbines synchronized to the grid experience total load rejection and are forced to shut down immediately. The turbine runner accelerates to runaway speeds in a few seconds, inducing high-amplitude, unsteady pressure loading on the blades. This sometimes results in a failure of the turbine components. Moreover, the unsteady pressure loading significantly affects the operating life of the turbine runner. Transient measurements were carried out on a scale model of a Francis turbine prototype (specific speed = 0.27) during an emergency shutdown with a transition into total load rejection. A detailed analysis of variables such as the head, discharge, pressure at different locations including the runner blades, shaft torque, and the guide vane angular movements are performed. The maximum amplitudes of the unsteady pressure fluctuations in the turbine were observed under a runaway condition. The amplitudes were 2.1 and 2.6 times that of the pressure loading at the best efficiency point in the vaneless space and runner, respectively. Such high-amplitude, unsteady pressure pulsations can affect the operating life of the turbine.

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Figures

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Fig. 1

Test rig of the model Francis turbine and the measurement locations outside the turbine; PTX1 and PTX2 are the pressure transmitters located 4.87 and 0.87 m from the casing inlet and Δp is the differential pressure across the turbine measured at the casing inlet and the draft tube outlet

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Fig. 2

Operating parameters of the model and the prototype Francis turbine

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Fig. 3

Data acquisition systems and locations of the pressure sensors PTX1, PTX2, VL01, P42, P71, S51, DT11, and DT21 mounted on the model turbine for the pressure measurement

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Fig. 4

Uncertainties of the mounted pressure sensors determined during the calibration

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Fig. 5

Operating points considered for the transient measurements of the emergency shutdown with a transition into total load rejection and the steady-state measurements at the runaway speed

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Fig. 6

Example of the raw and instantaneous mean pressure signals acquired by the sensor VL01 (vaneless space) during the emergency shutdown with a transition into total load rejection from the BEP: t = 0–7 s corresponds to the steady-state BEP load, t = 7 s corresponds to the point of emergency shutdown, t = 9 s corresponds to the transition into total load rejection, and t = 11 s corresponds to the observed runaway speed of the model turbine runner

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Fig. 7

Transient variation of the pressure at VL01 normalized by the reference pressure (ρE) of the corresponding operating condition

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Fig. 8

Transient variation of the fluctuating pressure at VL01 during the emergency shutdown with a transition into total load rejection from the BEP load for the time t = 7 to 17 s: (1) point of emergency shutdown, (2) transition into total load rejection, and (3) runaway condition

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Fig. 9

Constant efficiency hill diagram of the model Francis turbine (D = 0.349 m, H = 12 m), where the circle indicates the selected operating points for the emergency shutdown and the transition to total load rejection, the vertical dotted line at nED = 0.18 indicates the dimensionless synchronous speed of the model and the prototype turbine runner, BEP refers to the best efficiency point (ηh = 93.4%, nED = 0.18, and QED = 0.15), and α corresponds to the angular positions of the guide vanes in degrees [40]

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Fig. 10

Dimensionless pressure fluctuations in the runner (P42 and P71), vaneless space (VL01), and the draft tube (DT11) under the BEP operating condition of the model Francis turbine; the time length 0.5 s corresponds to 2.7 cycles of the runner

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Fig. 11

Instantaneous angular velocity (vgv) of the guide vane closing during the total load rejection (phase II) for the BEP and full-load transient conditions

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Fig. 12

Transient variation of the discharge (Q), guide vane angular position (α), runner angular speed (n), and electromagnetic torque (Te) during the emergency shutdown with a transition into total load rejection from the BEP load

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Fig. 13

Transient variation of the discharge (Q), guide vane angular position (α), runner angular speed (n), and the electromagnetic torque (Te) during the emergency shutdown with a transition into total load rejection from the full load

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Fig. 14

Transient variation of the net head (HM) and the pressure at the turbine inlet (PTX2) during the emergency shutdown with a transition into total load rejection from the BEP and full load

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Fig. 15

Spectrogram of the transient frequency variation at the inlet pipeline location PTX1 during the emergency shutdown with a transition into total load rejection from the full load

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Fig. 16

Transient pressure variation at the runner upstream (vaneless space) and downstream (draft tube) during the emergency shutdown with a transition into total load rejection from the BEP and full load

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Fig. 17

Spectrograms of the transient variation of the blade passing frequency and the dimensionless pressure amplitudes in the vaneless space (VL01) during the emergency shutdown with a transition into total load rejection from the BEP and full load

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Fig. 18

Velocity triangles at the runner inlet under the BEP and runaway conditions, i.e., t < 1 s and t = 4.8 s. Subscript 1 represents the velocity inlet to the runner, u is the tangential velocity in m s−1, vf is the flow velocity in m s−1, vr is the relative velocity in m s−1, v is the absolute velocity in m s−1, vu is the whirl component of the velocity in m s−1, α = is the guide vane angular position in degrees, and β is the blade angle in degrees.

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Fig. 19

Transient pressure variation at the locations P42 and P71of the runner blade during the emergency shutdown with a transition into total load rejection from the BEP and full load

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Fig. 20

Comparisons of the pressure pulsations under the three operating conditions: the BEP (α = 9.9 deg), runaway speed at the guide vane angular positions of 9.9 deg and 14 deg acquired at five locations, vaneless space (VL01), blade pressure side (P42), blade suction side (S51), blade trailing edge (P71), and the draft tube cone (DT11)

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Fig. 21

Spectral analysis of the pressure–time signals at five locations: the vaneless space (VL01), blade pressure side (P42), blade suction side (S51), blade trailing edge (P71), and the draft tube cone (DT11) under the runaway conditions for the guide vane positions of 9.9 deg and 14 deg.

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