Design note on surge shaft
Transcript of Design note on surge shaft
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
TABLE OF CONTENTS
Sr. No. DESCRIPTION
1. Design of Surge Shaft
(1.1) Location(1.2) Hydraulic Design(1.3) Structural Design(1.4) Others
2. Appendix
(2.1) Diameter of surge Shaft using Thoma Criteria(2.2) Area of Restricted Orifice using Calame & Gaden equation(2.3) Maximum Up-Surge Level in Surge Tank(2.4) Minimum Down- Surge Level in Surge Tank(2.5) Speed Rise(2.6) Pressure Rise(2.7) Structural Design of Surge Shaft
3. Drawings
4. Quantities
(4.1) Summery of quantities Estimation(4.2) Detailed quantities Estimation
5 Construction Planning
(5.1) Constructional Methodology(5.2) List of Equipments
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
(1) SURGE SHAFT DESIGN (WRITE UP)
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
1. SURGE SHAFT
1.1 Location
Surge shaft has been located on the ridge with flat topography with general
ground elevation of El. 536.58 m. The location shall be accessible from
existing road by taking off an additional branch road.
1.2 Hydraulic Design
Hydraulic Design of the surge tank has been carried out using IS: 7396 (Part-
1) – 1985. A restricted orifice type surge shaft has been assumed.
According to Thoma criteria with a factor of safety of 1.6, minimum area
required for the surge shaft works out to 562.8 sq.m, (Appendix 2.1), with
diameter of 26.7 m. Since the construction of such huge diameter surge shaft
in this project geology is difficult as such provision of upper and lower
expansion gallery has been envisaged with a constructible surge shaft
diameter, from the earlier experience and available running project of similar
magnitude. The surge shaft of 16 m diameter with restricted orifice adopted
for study with a provision of 5 m diameter D- shaped 122 m long lower and
210 m long upper expansion galleries with a slope of 1 in 150 m.
TO verify these dimensions and arrangement of surge shaft a study of surge
analysis and speed rise and pressure rise was done by using WHAMO (Water
Hammer and Mass Oscillation) of USACE.
The size of the orifice has been calculated to satisfy the condition given by
Calame and Gaden (Appendix 2.2). An orifice size of 7.8 sq. m. is provided.
On the perusal of results after running this model following inference has been
notified. The maximum upsurge level in the surge tank has been worked out
corresponding to the full load rejection at the highest reservoir level. Maximum
upsurge level works out to be El. 532.5 m. Considering a freeboard, the top
of the surge tank has been kept at El. 536.5 m (Appendix 2.3).
The minimum down surge has been calculated considering 100% load
rejection followed by full load acceptance at the instant of maximum negative
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
velocity in the head race tunnel at minimum reservoir level .This gives the
maximum down surge level of El. 503.3 m (Appendix 2.4). The invert of the
HRT (El.482.75 m) has been kept sufficiently below this level so as to ensure
sufficient water cover over the tunnel overt to avoid vortex formation.
Speed rise (Appendix 2.5),
Pressure rise (Appendix 2.6),
The height of the surge tank from the crown of HRT (El.489.75 m) to the top of the surge shaft (El. 536.58 m) works out to be 46.83 m.
1.3 Structural Design
The surge shaft with RCC lining has been envisaged to sustain the fluctuating
water column. (Appendix 2.7).
To restrict /check the loss of water i.e. impervious conditions.
To restrict the skin failure / crack of concrete.
The thickness of lining has been designed on the basis of Lame’s
theory of thick cylinder keeping in view to sustain the external pressure,
when the shaft is drained.
1.4Others
The surge shaft shall be provided with a vertical slide type gate at the
downstream end to close the penstock / pressure shaft for inspection and
maintenance.
The surge shaft details have been provided in drawing nos. ________
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
(2) APPENDIX
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
APPENDIX 2.1
WORKING SHEET FOR THE CALCULATION OF DIAMETER OF SURGE
SHAFT:
A surge tank has been envisaged at the downstream end of the HRT to
provide the open reflection column of water to limit the transmission of water
surges due to water hammer phenomenon to HRT. The surge tank would
also assist in improving the regulation and to provide water supply to turbines
in case of sudden start up of a machine.
In order to determine the dimensions of surge tank, following assumptions has
been adopted:
To ensure the hydraulic stability of surge tank, its area has been calculated
according to Thomas criteria. According to Thomas, the limit cross sectional
area of surge tank is
Where,
L = Length of HRT = 8400 m
Diameter of HRT = 7.0 m (Horse shoe Shaped tunnel)
At = Cross sectional area of HRT = 0.8293*7.02 = 40.6357 m2
H = Net head = 80.23 m
Q = Design Discharge = 116 m3/sec.
Flow velocity in HRT,
R = Hydraulic Mean Radius = 1.78 m
= Resistance factor of tunnel,
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
The value of resistance factor is function of total head loss in water conductor
system excluding the Head Loss in pressure shaft and tail race tunnel.
As per IS: 7396 – (Part-I) – 1985
The value of shall be determined from the following formula:
v2 = + other losses in tunnel system
Considering other losses is tunnel system is within 10% of friction loss in
tunnel.
Cross-sectional area of surge tank required
should be calculated for the value of n are n = 0.012 n = 0.018
As per Thoma criteria minimum value of shall be used in the above formula.
When ‘n’ is to be considered as equal to 0.012
v2 = 1.1 = 1.1
1.1 [4.5779] = 5.03569
= 0.6179 sec2/m
When ‘n’ is to be considered as equal to 0.018
v2 = 1.1 = 1.1
1.1 [10.3] = 11.330
= 1.390 sec2/m
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
As per Thoma criteria for calculation of diameter of surge shaft tank minimum
value of is to be taken.
The cross sectional area of Surge Tank required, for n=0.012 ,β=0.6179
=
Asth = 351.75 sq.m.
Factor of safety for restricted orifice surge shaft, 'n' = 1.6
(IS: 7396 (Part 1)-1985, Clause 5.4)
Required area Asth = 1.6 x 351.75 = 562.8 sq.m.
Required diameter of surge tank, D =
D =26.76 m
Provide diameter of surge tank = 16 m, with area = 200.96 m2
\APPENDIX 2.2
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
AREA OF RESTRICTED ORIFICE USING CALAME AND GADEN
EQUATION:
Surge column shall depend upon the restriction provided by the orifice in the
bottom of surge shaft. According to IS: 7396 (Part 1)-1985 clause-5.5.3 &
5.5.3.1 the area of orifice is so chosen as to satisfy the condition given by
Calame and Gaden for maximum flow which is as fallow:
Where
hor = Head loss offered by orifice
Z* = Surge height corresponding to change in discharge neglecting
friction and orifice loss
= Head losses in head race tunnel = v2 = 5.02 m
At the time of instantaneous closure from maximum discharge, the amplitude
of maximum surge in case of undammed mass oscillation is given by
And,
The Surge will depend on resistance offered by an orifice of area A0 as = 7.79
m2. Thus size and shape of orifice should be decided first and resistance shall
be calculated by equation.
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
Where,
Cd is the coefficient of discharge.
Choosing A0 as = 7.79 m2 and Cd = 0.62 for rectangular gate slot.
Resistance offered by orifice
27.82 m < 29.41 m < 30.33 m
Thus, satisfying the Calame and Gaden condition
Hence, envisaged the area of orifice is = 7.8 m2.
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
APPENDIX 2.3
MAXIMUM UPSURGE LEVEL IN SURGE TANK
According to IS: 7396 (Part 1) – 1985, the surge tank shall be designed to accommodate the maximum and minimum water levels anticipated under worst condition.
The maximum upsurge level in the surge tank shall be worked out corresponding to:
a) The full load rejection at the highest reservoir level and,
b) Where considered necessary specified load acceptance followed by full load rejection at the instant of maximum velocity in the head race tunnel and higher of the two shall be considered.
The surge analysis was done in WHAMO and checked according to IS: 7396. It was observed that the maximum upsurge did not occur in the ‘a’ condition i.e. for full load rejection at highest reservoir level.
The surge levels were also calculated for other cases like 100% load acceptance followed by full load rejection at highest reservoir level, 66% load acceptance followed by full load rejection at highest reservoir level and 33% load acceptance followed by full load rejection at highest reservoir level .
It was observed from the result (shown in Table 2.3.1 and Fig.2.3.1 , Fig.2.3.2, Fig.2.3.3 & Fig.2.3.4) for restricted orifice type surge tank that the level of worst case of upsurge in surge tank, El.532.461 m occurs when full load rejection at highest reservoir level using WHAMO.
TABLE-2.3.1RESERVOIR LEVEL (FRL) LOADING CONDITION UP-SURGE
ft m ft m1712.5776 522 100-0 1746.90 532.461
1712.5776 522 0-100-0 1734.10 528.560
1712.5776 522 0-66-0 1725.60 525.969
1712.5776 522 0-33-0 1722.50 525.024
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
Fig.2.3.1
Fig. 2.3.2
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
Fig. 2.3.3
Fig. 2.3.4
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
APPENDIX 2.4
MINIMUM DOWNSURGE LEVEL IN SURGE TANK
According to IS: 7396 (Part 1) – 1985, the surge tank shall be designed to
accommodate the maximum and minimum water levels anticipated under worst
condition.
To obtain minimum down surge level the worst of the following two conditions
shall be considered:
a) The full load rejection at minimum reservoir level followed by specified
load acceptance at the instant of maximum negative velocity in the head
race tunnel, and
b) Specified load acceptance at load or speed-no-load condition at the
minimum reservoir level.
The surge analysis was done in WHAMO and checked according to IS: 7396. It
was observed that the minimum downsurge did not occur in the ‘b’ condition i.e.
for 100% load acceptance at no-load condition at the minimum reservoir level.
The surge levels were also calculated for other cases like 100% load rejection
followed by full load acceptance at the instant of maximum negative velocity in
the head race tunnel, 100% load rejection followed by 66% load acceptance at
the instant of maximum negative velocity in the head race tunnel and 100%
load rejection is followed by 33% load acceptance at the instant of maximum
negative velocity in the head race tunnel.
It was observed from the result (shown in Table 2.4.1 and Fig.2.4.1,Fig.2.4.2 ,
Fig.2.4.3 & Fig.2.4.4) for restricted orifice type surge tank that the level of
worst case of downsurge in surge tank, El.503.291 m occurs when 100% load
rejection is followed by 100% load acceptance at the instant of maximum
negative velocity in the head race tunnel using WHAMO.
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
TABLE – 2.4.1
Fig.2.4.1
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
RESERVOIR LEVEL (MDDL)
LOADING CONDITION
DOWN-SURGE
ft M ft m
1692.8928 516 100-0-100 MDDL 1651.2 503.291
1692.8928 516 0-100 MDDL 1656.8 504.998
1692.8928 516 100-0-66 1669.6 508.900
1692.8928 516 100-0-33 1669.6 508.900
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
Fig.2.4.2
Fig.2.4.3
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
Fig.2.4.4
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
APPENDIX 2.5
STRUCTURAL DESIGN OF SURGE SHAFT
According to IS: 7357 – 1974, the thickness of lining for surge shaft shall be
designed on the basis of Lame’s thick cylinder theory. For designing purpose,
the worst condition occurs from outside the lining. The lining shall be
adequate to withstand this anticipated external pressure. Indian standards
suggest providing a minimum thickness of 0.3m or thickness required to resist
maximum external pressure, whichever is higher.
Circumferential stress in lining is determined by
Pc =
Where,
Pc = External (circumferential) pressure, Kgf/ cm2.
= Permissible comp. stress in concrete, Kgf/ cm2
= 0.446 fck N/mm2 (Refer IS: 456 – 1978)
For M25 grade concrete,
fck, Characteristic strength of concrete = 25 N/mm2
= 11.15 X 10.1971 Kgf/cm2.
= 113.70 kg/cm2.
a is the internal radius of shaft = 8 m
b is the external radius of shaft (including thickness of lining)
a = 800 cm
Pc = External circumferential stress (Pressure)
Pc = External water Pressure corresponds to 46.69 m height of water.
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
46.69 m of water = 4.66 kgf/cm2
4.66xb2 + (64 x 4.66) = 113.70b2 – 113.70 x 64
64 [4.66 + 113.70] = 113.70b2 – 4.66b2
64 x 118.36 = 109.04x b2
7575.04 = 109.04x b2
b2 = 69.4702
b = 8.33
Thickness of lining = (b-a) = (8.33 – 8) m
= 0.33 m
Provide 500 mm thick RCC lining for surge shaft.
__________________________________________________________________________________TECHNICAL MEMORANDUM ON SURGE SHAFT
YAMNE STAGE –II H.E.P (84 MW)_________________________________________________________________________
(3) DRAWINGS
__________________________________________________________________________________ TECHNICAL MEMORANDUM ON SURGE SHAFT