Francis turbine part load resonance risk analytical assessment

Francis turbine part load resonance risk analytical assessment

C. Nicolet, C. Landry, S. Alligné, A. Béguin

SHF/AFM 2019, Sion, Switzerland, November 06-07,2019

Power Vision Engineering sàrl1, ch. des Champs-CourbesCH-1024 EcublensSwitzerlandhttp://www.powervision-eng.ch

http://www.powervision-eng.ch/

2

Contents• Context and key goals

• Eigenvalue computation

✓Numerical equations

✓Analytical equations

• Examples of application

✓Hydraulic system 1



• Conclusions / Take away message

3










Context and Key goals

4

• Massive penetration of alternative renewable energies (Solar, wind power)

• Stochastic nature of the renewable energy production

Mean annual growth rates of electricity production 2002-2012

• To maintain balanced production:✓ Sufficient reserve capacity

✓ Primary and secondary control capabilities

→ Hydropower plants

→ Off-design operation

Context and Key goals

• Frequent power transients:✓ Require a wide operating range

✓ May induce high levels of vibration and large pressure fluctuations

Part load condition

[0.2 – 0.4] • Turbine rotational speed

* Favrel et al., 2013

HYPERBOLE (ERC/FP7-ENERGY-2013-1-Grant 608532)

Full load condition

* Müller et al. ,2013

7










SIMSEN software

Modelingfrom

water to wire 8

• SIMSEN software✓ Hydraulic circuit

✓ Electrical installations

✓ Rotating inertias

✓ Control system

Electrical Analogy• Mass and momentum equations:

• Electrical analogy:✓ (Bergeron, 1950; Paynter, 1953 )

R/2Lh/2Lh/2

C

Rh

R/2

Hi

Hci

Qi QiHi+1

2

0H a Q

t gA x

+ =

02

12

=+

+

Q

gDA

Q

t

Q

gAx

H

0

01

=+

+

=

+

IRt

IL

x

U

x

I

Ct

U

ee

e

Storage

Losses

Inertia

Datum.

Q1Q2

D, a, dx

H1 H2

• Assumptions:✓ Uniform flow

✓ 1-D approach

✓ Convective terms neglected

✓ Vertical displacements neglected

Eigenvalue computation

10

• Set of differential equations

( ) ( )XdX

A B X X Cdt

+ =

• Small perturbation

0X X X= +

( )( )

0

0

d X Xf X X

dt

+= +

1det 0

l lI s A B

−

+ =

• Eigenfrequency

11










Natural frequencies

12

• Hydraulic system modelled by an equivalent pipe

1

n

tot ii

l l=

=

1

totequ n

i

ii

la

la

=

=

2

equ equk

totk

a af k

l= =

Total length Equivalent wave speed Natural frequency (Order k)

Standing wave

First natural frequency of the cavitating draft tube

13

• Simplified hydroacoustic model of the frictionless cavitating draft tube

2DT DT

DTDT

l g AC

a

= DT

DT DT

lL

g A=

1 1 12 2

DTo

DTDT DT

af

lL C = =

lDT = DT length [m]ADT = DT cross section area [m2]aDT = DT wave speed [m/s]

* Jacob, 1993

Draft tube

Cavitation compliance Draft tube inductance First natural frequency

Sim

ilar

to

a s

pri

ng–

mas

s sy

stem

𝑘 ≈1

𝐶𝐷𝑇𝑚 ≈ 𝐿𝐷𝑇 𝑓0 =

1

2π

𝑘

𝑚≈

1

2π

1

𝐶𝐷𝑇𝐿𝐷𝑇

𝑘

𝑚

1 1 12 2

DTo

TR DT DTDT TR

TR

af

L C Al l

A

= =

First natural frequency of the cavitating draft tube

14

• Simplified hydroacoustic model of the frictionless cavitating draft tube

lTR = TR pipe length [m]ATR = TR pipe cross section area [m2]

TRTR

TR

lL

g A=

* Dörfler, 2013

Draft tube

2DT DT

DTDT

l g AC

a

=

Cavitation compliance Tailrace pipe inductance First natural frequency

12

DTo

DTDT TR

TR

af

Al l

A

=

Analytical equations

15

• Summary

1st order1

2DT

oDT

af

l=

2equ equ

ktotk

a af k

l= =

2equ equ

ktotk

a af k

l= =

2equ equ

ktotk

a af k

l= =

1 2equ equ

totk

a af

l= =

2nd-6th order

Equivalent pipe

Draft tube without TR

Draft tube with TR

16










Example of applications

17

• Hydraulic system 1

PenstockL = 300 mD = 1.2 ma = 1’250 m/sλ = 0.012 -

Draft tubeL = 10 mD = 1.2 ma = [50-100] m/sλ = 0.012 -

TurbinePn = 5 MWQn = 5.0 m3/sHn = 100 mWCNn = 750 rpmDref = 0.846 mNq = 53 -

Nn = 750 rpm = 12.5 Hz➔fexcitation = [0.2 – 0.4]·fn

➔fexcitation = [2.5 – 5 Hz]



1st Pressure mode 1st Discharge modeElastic mode shape

Elastic mode shape✓ Non-Linear amplitude variation of

pressure in the TR as function of the length

✓ Non-constant amplitude variation of discharge in the TR as function of the length

11

12

equ equ

tot

a af

l= =

1

2DT

oDT

af

l=

Analytical

calculation

Eigen value

calculation

a DT (min) a DT (min) Relative error

[m/s] [m/s] [%]

f0 [Hz] 0.8 1.24 -35.48

f1 [Hz] 1.14 1.24 -8.06

f2 [Hz] 2.27 2.09 8.61

f3 [Hz] 3.41 3.67 -7.08

f4 [Hz] 4.55 4.18 8.85

f5 [Hz] 5.68 5.99 -5.18

f6 [Hz] 6.82 6.15 10.89

System 1



fexcitation = [2.5 – 5 Hz]

• 1st order: Better agreement with f1

• 2nd-6th order: Rather good agreement for natural frequencies Maximum error of 14%.

• Risk of resonance with the draft tube in red.

a =

50

m/s

11

12

equ equ

tot

a af

l= =

1

2DT

oDT

af

l=

20











21



Tailrace pipeL = 100 mD = 1.2 ma = 1’250 m/sλ = 0.012 -







1st Pressure mode 1st Discharge modeRigid column mode shape

Rigid column mode shape✓ Linear amplitude variation of

pressure in the TR

✓ Constant amplitude variation of discharge in the TR

→ Similar to surge tank mass oscillation between TR pipe and DT compliance

11

12

equ equ

tot

a af

l= =

12

DTo

DTDT TR

TR

af

Al l

A

=

Analytical

calculation

Eigen value

calculation

a DT (max) a DT (max) Relative error

[m/s] [m/s] [%]

f0 [Hz] 0.5 0.55 -9.09

f1 [Hz] 1.19 0.55 116.36

f2 [Hz] 2.38 2.1 13.33

f3 [Hz] 3.57 4.05 -11.85

f4 [Hz] 4.76 4.88 -2.46

f5 [Hz] 5.95 6.18 -3.72

f6 [Hz] 7.14 6.36 12.26

System 2

Analytical

calculation

Eigen value

calculation


[m/s] [m/s] [%]

f0 [Hz] 0.25 0.27 -7.41

f1 [Hz] 0.96 0.27 255.56

f2 [Hz] 1.92 2.04 -5.88

f3 [Hz] 2.88 2.53 13.83

f4 [Hz] 3.85 4.12 -6.55

f5 [Hz] 4.81 4.87 -1.23

f6 [Hz] 5.77 5.16 11.82

System 2




• 1st order: Good agreement with f0



a =

50

m/s

a =

10

0 m

/s

11

12

equ equ

tot

a af

l= =

12

DTo

DTDT TR

TR

af

Al l

A

=

24











25



Tailrace pipeL = 100 mD = 2 ma = 1’250 m/sλ = 0.012 -








1st Pressure mode 1st Discharge modeRigid column mode shape

Rigid column mode shape✓ Linear amplitude variation of

pressure in the TR

✓ Constant amplitude variation of discharge in the TR

→ Similar to surge tank mass oscillation between TR pipe and DT compliance

11

12

equ equ

tot

a af

l= =

12

DTo

DTDT TR

TR

af

Al l

A

=

Analytical

calculation

Eigen value

calculation

a DT (max) a DT (max) Relative error

[m/s] [m/s] [%]

f0 [Hz] 0.84 0.81 3.70

f1 [Hz] 1.19 0.81 46.91

f2 [Hz] 2.38 2.1 13.33

f3 [Hz] 3.57 4.03 -11.41

f4 [Hz] 4.76 4.72 0.85

f5 [Hz] 5.95 6.14 -3.09

f6 [Hz] 7.14 6.55 9.01

System 3

Analytical

calculation

Eigen value

calculation


[m/s] [m/s] [%]

f0 [Hz] 0.42 0.42 0.00

f1 [Hz] 0.96 0.42 128.57

f2 [Hz] 1.92 2.04 -5.88

f3 [Hz] 2.88 2.55 12.94

f4 [Hz] 3.85 4.12 -6.55

f5 [Hz] 4.81 4.84 -0.62

f6 [Hz] 5.77 6.16 -6.33

System 3




• 1st order: Good agreement with f0



a =

50

m/s

a =

10

0 m

/s

28










29

Conclusions• Analytical approach to determine the possible risk of resonance with the draft tube vortex rope

excitation (2.5-5Hz)

• 1st order: Better agreement with f1 for the hydraulic system without a tailrace pipe (hydraulic system 1) → Elastic mode shape

• 1st order: Good agreement with f0 for the hydraulic system with a tailrace pipe (hydraulic system 2 & 3) → rigid column mode shape

• 2nd-6th order: Rather good agreement for natural frequencies (Maximum error of 14%).

• Limitations of the methodology✓ Parallel branches:

• Modelling by a single branch with equivalent parameters to obtain a first order of magnitude.• Real system will feature much more complex and numerous eigenvalues (hydraulic system asymmetry, diameters,

bifurcations)

30

Take away Message• This analytical method is included as ANNEXE E.2 of the new IEC

Technical Specification 62882 ED1 (to be issued in 2020)

12

DTo

DTDT TR

TR

af

Al l

A

=

2equ equ

ktotk

a af k

l= =

Without a tailrace pipe

With a tailrace pipe

2equ equ

ktotk

a af k

l= =

2equ equ

ktotk

a af k

l= =

1st order

1st order

2nd–6th order

2nd–6th order

Hydraulic machines – IEC Technical specification for Francis turbine pressure fluctuation

Thank you for your attention!

Power Vision Engineering Sàrl1, ch. Des Champs-CourbesCH-1024 [email protected]

31

http://www.powervision-eng.ch/

32


Francis turbine part load resonance risk analytical assessment

Documents

Transcript of Francis turbine part load resonance risk analytical assessment