GUIDE LINES FOR SIZING HYDRANT GUIDE LINES FOR SIZING HYDRANT TURBINES, GENERATOR & POWERTURBINES, GENERATOR & POWERHOUSE DIMENSIONINGHOUSE DIMENSIONING

- Widely used method of sizing turbines, developed by U. S. Bureau of Reclamation (USBR) in 1972.

- Used experience curves of turbine units manufactured from 1951 to 1972.

- Specific speed as the fundamental performance characteristic to which all other turbine characteristics are related.

- Now new & more useful methods of selecting sizing turbines & generators have been developed during last 30 years.

- Empirial equations / experience curves have been developed to select turbine runner speed, diameter & other parameters.

Basic Data RequiredBasic Data Required

- Rated output of unit including overload.

- No. of units.

- Max., Min. & Rated Head

- H. Race & T. Race water level under various load conditions

- Water conductor system

- Temp. of water, Altitude

At feasibility stage-preliminary information about turbine, generator, MIV for PH size.

REFERENCES :

1. ISS 12837 : 1989 Hydraulic Turbines for Medium and Large Power Houses -Guidelines for Selection

2. ISS 12800 (Part-1): 1993

Guidelines for Selection of Turbines, Preliminary Dimensioning and Layout of Surface Hydro-Electric Power House

Part-1 – Medium and Large Power Houses

Part-2 – Storage Power Houses

3 – Mini & Micro Power Houses

3. ISS 5496:1969 Guide for Preliminary Dimensioning and Layout of Elbow Type Draft Tubes for Surface Hydel Power Stations

4. ISS 7418 : 1991 Criteria for design of spiral casing (concrete

and steel) (first revision)

5. Guidelines for Preliminary Dimensioning of Hydro Power Stations by S.P. Singh, Rudra Dev & Pratap Narain

SOME DEFINITIONS & EXPLANATIONS POWER DEVELOPED BY A TURBINE

P = 9.81 Q.H.

Where P = TURBINE OUTPUT IN ‘KW’Q = DISCHARGE PASSING

THROUGH TURBINE IN ‘M3/SEC’

H. = NET HEAD IN ‘METRES’ = TURBINE EFFICIENCY IN

PERCENT

SPECIFIC SPEED

NS =N √P

H 5/4

Where NS = SPECIFIC SPEED N = TURBINE SPEED IN rpmP. = RATED TURBINE OUTPUT IN

METRIC HORSE POWER H = RATED NET HEAD IN

METRES

SPECIFIC SPEED (NS) The speed in rpm at which a given turbine would rotate, if reduced homologically in size, so that it would develop 1 metric horsepower (i.e. 736 watts) under 1 metre of head at full gate opening.

Minimum Tail Water Level

Water level in the tail race at the exit end of the draft tube corresponding to a discharge required to run one machine at no load.

Submergence

Difference in elevation of minimum tail water level above distributor centre line or runner centre line.

EFFICIENCY OF TURBINE / GENERATOR & RATED TURBINE OUTPUT

For computing turbine output at rated / design head conditions :

Generator = 98%

Francis Turbine = 95%

Kaplan Turbine = 94%

Pelton Turbine = 91%

SYNCHRONOUS SPEED

- Determine trial specific speed (Ns) corresponding to rated head.

- Trial synchronous speed/rotational speed ‘N’:

N’ = Ns H 5/4

√P x 1.358

- The rotational/synchronous/rated speed of the turbine:

N (in rpm) = 120 x f

þ

f = Frequency in cycles per second (50c/s.),

þ = number of pair of poles

- The Selection of rated speed :

a) An even number of poles (preferably divisible by four) - preferred.

b) If rated head vary less than 10% from the design head, next greater speed chosen. Heads varying excess of 10% use next lower speed. Heavy silt laden water, lower speed.

- After determining rated speed is calculated, the specific speed :

Ns = N√ P x 1.358

H 5/4

TURBINE SETTING In reaction turbines, setting w.r.t. cavitation. The suction height of distributor above the minimum tail water level determined by:

Hs ≤ Hb - σH - Hv

Hs = Suction head

Hb = Barometric pressure of water column;

Hv = Vapour pressure;

(Hb - - Hv determined from Curve for a given altitude and for a temperature 250 C).

σ = Thoma’s cavitation co-efficient, obtained from

Curve

The positive value of Hs - center line of the distributor above the minimum tail water level. The negative value below minimum tail water level.

The relationship between specific speed (Ns) and peripheral velocity coefficient (Ku) is shown in Curve.

- The rotational/synchronous/rated speed of the turbine:

RUNNER

- The other runner dimensions obtained with respect to the diameter D3 and specific speed Ns from the curves..

Ku = π D N

60 √2 gH

D = D3 for Francisfor FrancisD = Dn for Kaplanfor Kaplan

- Metallic Spiral casing used for gross heads generally above 30 metres. Dimensions of the spiral casing obtained as a function of Ns..

SPIRAL CASING

- For Lower Heads..

Metallic Spiral Casing

Concrete Spiral Casing

Plate Thickness of Scroll Case

t = D x P

2 x L

FD = Diameter of scroll case P = Pressure L = Ultimate Load in kg/cm2 (3200kg/ sq. cm. for steel)F = Factor of Safety

- Major dimensions of the draft tube determined in accordance with IS 5496:1969. Usually, an elbow type draft tube used for medium & large size units because more efficient and requires less excavation.

- Height of the draft tube at exit end (h)

DRAFT TUBEDRAFT TUBE

- Depth of draft tube (H1)..

h = 0.94 D3 to 1.32 D3

Higher value for lower specific speed

H1 = 2.5 to 3.0 D3

- Length of draft tube (L)..

L = 4 to 5 D3

- Clear Width of draft tube at exit end (B)..

B = 2.6 to 3.3 D3

Width of draft tube excessive (>6 m), a pier of 1.5 metres width in the center of the draft tube.

For underground power stations, no pier.

The area of the exit end of draft tube should reduce the water exit velocity to about 2 m/Sec.

- Selection Type of Generator Bearing Arrangement

speed ≤ 300 rpm - umbrella or semi-umbrella type,

speed > 300 rpm - ordinary type.

MAIN PARAMETERS OF HYDRO MAIN PARAMETERS OF HYDRO GENERATORSGENERATORS

- The air gap diameter and active length of the core determined by output and synchronous speed of the generator from Curves.

- The air gap diameter should be large enough to allow the turbine runner / top cover to pass through the stator bore

Air Gap Diameter (Dg) & Active Core Length (Lc)

- Outer Core Diameter (Do).

- Stator Frame Diameter (Df)..

- Inner Diameter of Generator Barrel (Db).

D0 = Dg ( 1 + π ) 2p

where

þ = number of pairs of poles.

Df = (D0 + 1.2 ) meters.

Suspended type construction

Db = (Df + 2.3 to 2.8) metres

= (Do + 3.5 to 4.0) metres

- Height of Load Bearing Bracket (hj)..

Lf = (Lc + 1.5 to 1.6) meters.

Db = (Df + 1.6 to 2.0) metres

= (Do + 2.8 to 3.2) metres

hj = K √ Df for suspended type construction, and

hj = K √ Dg for umbrella type construction.

K = 0.65 for load < 50 tonnes per arm

of the bracket.K = 0.75 for load of 50 to 100

tonnes per arm of the bracket, K = 0.85 for a load of 100 tonnes

and above per arm of the bracket.

Umbrella/Semi-Umbrella type

- Number of Arms of Brackets.

Decided on total load on the thrust bearing that is maximum hydraulic thust of the turbine runner and weight of rotating parts,. Generally 4 to 8 arms of the bracket are taken.

- Axial Hydraulic Thrust (Pa).Pa = KD2, Hmax in tonnes

Where,

K = a constant,

D1 = inlet diameter of runner,

Hmax= maximum head.

- Weight of Generator Rotor (Wn).

Weight (Wn) of generator rotor in relation with air gap diameter ( Dg ) and active core length (Lc ) can be determined from Curve. The values multiplied by the active core length (Lc) to get the rotor weight.

- Weight of Turbine Runner.

Weight of turbine runner can be determined from Curve

OVERALL DIMENSIONS OF POWER OVERALL DIMENSIONS OF POWER HOUSEHOUSE

- Mainly depend upon the following:

a) Overall dimensions of the turbine, draft tube and scroll-case;

b) Overall dimensions of the generator;

c) Number of units in the power house; and

d) Size of the erection/service bay.

e) Location of main inlet valve, if any.

- Depends upon the unit spacing, length of erection bay and the length for the E.O.T. crane to handle the last unit. Length of erection bay 1.0 to 1.5 times the unit bay size..

Length of Power House

UNIT SPACINGUNIT SPACING

- Outer dimensions for the generator barrel, the inner diameter increased by 0.5 to 1.5. A clearance of 1.5 to 2.0 m added to either side to determine the unit spacing. Concrete thickness on either side of scroll case should be at least 2.0 to 2.5m in case of concrete scroll case and 1.0 to 1.5 m in case of fully-embedded steel scroll case..

Total length (L) of Power House : :

L = No. x ( unit spacing) + Ls + K

No = Number of units

Ls = Length of erection bay,

K = Length required for the E.O.T. crane to handle the last unit. usually 3.0 to 5.0 metres.

WIDTH OF POWER HOUSEWIDTH OF POWER HOUSE

On the upstream side provision should be made for the following..

a) 1.5 to 2.0 m for concrete on the upstream of scroll case;

b) A gallery of 1.5 to 2.0 m width for approaching the draft tube manhole;

c) Main inlet valve pit to be provided as per IS 7326 (Part I) : 1992 and IS 7332 (Part I) : 1991.

i. For butterfly valve – width of 0.8x inlet dia of scroll case

ii. For spherical valve – width of 2.3 to 2.6 x inlet dia of scroll case. Inlet valve gallery utilized for approaching the draft tube man-hole and no separate gallery.

d) 1.5 to 2.0 metres for pressure relief valve in the scroll case if required; and

e) The spaces sufficient for accommodating the auxiliary equipment also but may have to be reviewed.

- The height of power house from the bottom of the draft-tube to the centre line of the spiral casing (H1). Determined in accordance with IS 5496 : 1969. The thickness of the concrete below the lowest point of draft-dube 1.0 to 2.0 m.

- The height from center line of the spiral-casing up to the top of the generator (H2 ):

Height of Power House

H2 = Lf + hj + K

K - 5.5 to 7.0

- The height of the machine hall above the top bracket of the generator depends upon the E.O.T. crane hook level, crane rail level, and clearance between the ceilling and the top of the crane. Further, height depend upon the height of the service bay floor from where the equipment is handled.

- The E.O.T. crane hook level and crane rail level determined by:a) Hauling/moving major items viz.

runner, rotor, stator.b) Hauling the main transformer.c) Untaking transformers.d) Unloading of largest package from

the trailors - 7 to 8.5 metres.

The height of the power house above E.O.T. crane - 4 to 6.5 m depending upon the width and capacity of E.O.T. .3 metre between the highest part of crane and the ceiling.

CONCLUSION CONCLUSION

The guidelines are for preliminary selection of main parameters of the hydro generating equipment and overall dimension of the power house. However, the final detailed design shall depend on the hydrological, geological and other factors peculiar to each site and also the design practices followed by the manufacturing concerns supplying the equipment.