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IS 7396-3 (1990): Criteria for hydraulic design of surgetanks, Part 3: Special surge tanks [WRD 14: Water ConductorSystems]

4’ -. .

t ! wT3 matrjiidiiPt ._

Indian Standard

CRITERIA FOR HYDRAULICDESIGNOFSURGETANKS

PART 3 SPECIAL SURGE TANKS ’ ..”

UDC 627’846 : 624’04

.._

I-\ ’ : \

._’ @ BIS 1991

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

JunuuYy 1991 Price Group 3

Water Conductor Systems Sectional Committee, RVD 14

FOREWORD

This Indian Standard (Part 3 ) was adopted by the Bureau of Indian Standards on 27 March 1990, after the draft finalized by the Water Conductor Systems Sectional Committee had been approved by the River Valley Projects Division Council.

Part 3 deals with the surge tank which absorbs the water hammer or elastic shock waves coming from the pressure pipe line or tunnel on closure or opening of the valve or turbine gates and also to supply/store additional water during load acceptance/rejection during load demand/rejection until the conduit velocity has accelerated/decelerated to the new steady state value. Surges or mass oscillations occur in the surge tanks, the hydraulic design of which is so done as to keep the surges within reasonable limits.

Special surge tanks may be defined as simple or restricted orifice type surge tanks which have additional features like expansion galleries ( chambers ), spilling arrangements, etc. Air cushion surge chambers also fall under this category. Surge tanks with upper and/or lower expansion galleries are covered in this standard ( see Fig. 1 ).

The expansion galleries ( chambers ) are provided under the following conditions:

a) When the computed maximum and minimum surge levels are found to be higher/lower than the maximum and minimum levels of the surges fixed in accordance with IS 7396 ( Part 1 ) : 1985 ‘Criteria for hydraulic design of surge tanks: Part 1 Simple, restricted orifice and differential surge tanks’, IS 7396 ( Part 2 ) : 1985 ‘Criteria for hydraulic design of surge tanks: Part 2 Tail race surge tanks’ and IS 7396 (Part 4) : 1983 ‘Criteria for hydraulic design of surge tanks: Part 4 Multiple surge tanks’, based on the turbine characteristic ( see Fig. 2 ).

b) Many a times in case of conventional surge tanks, long approach tunnels are required to be constructed. Sometimes for economy a portion of the approach tunnel is utilized as an expansion gallery and the upper portion of the gallery serves as an air vent, if the maximum upsurge remains below the soffit at the mouth of the approach tunnel ( see Fig. 3 ).

This standard has been prepared in parts. Other parts of this standard are as follows:

IS 7396 ( Part 1 ) : 1985 Simple, restricted orifice and differential surge tanks (just revision )

IS 7396 ( Part 2 ) : 1985 Tail race surge tanks (first revision )

IS 7396 ( Part 4) : 1983 Multiple surge tanks

1 SCOPE

1.1 This standard (Part 3 ) lays down the criteria for hydraulic design of surge tanks with expansion galleries/chambers.

2 REFERENCES

2.1 The Indian Standard IS 7396 (Part 1 ) : 1985 is necessary adjunct to this standard.

3 TERMINOLOGY

3.1 For the purpose of this standard the definitions given in IS 7396 (Part 1 ) : 1985 shall

“PPlY*

4 DATA

4.1 The data required for the design of special surge tanks with upper/lower expansion gallery/ chamber shall be in accordance with IS 7396 (Part 1) : 1985.

4.2 At the time of design of surge system, the designer should ascertain the geological features around the location of the surge tank to the extent of 500 m.

5 DESIGN

5.1 Design Conditions

5.1.1 The maximum and minimum water levels ( A & B) in the surge tank shall be determined depending upon the turbine characteristics ( see Fig. 2 ) and the percentage to be allowed over the design head within the permissible safety of the machine.

5.1.2 The maximum and minimum water levels in the surge tanks ( c 8~ D) shall be found out in accordance with 5.1.1, 5.1.1.1 and 5.1.1.2 of IS 7396 (Part 1 ) : 1985. If these water levels work out to be higher/lower than worked out as under 5.1.1 of this standard, the necessity of upper expansion gallery or lower expansion gallery would arise.

6 TENTATiVE VOLUME OF UPPER EXPANSION GALLERIES/CHAMBERS

6.1 Draw the two curves 5 vs I and QT vs r as shown in Fig. 4 and 5 from the values obtained from 5.1.1, 5.1.1.1, 5.1.1.2 of IS 7396 (Part I ) :

1985. Draw the line XT in Fig. 4 at the point A of Fig. 2. Draw the modified QLT Curve as AX’ 2” CD ( Fig. 5 ). Find out the volume as below:

Volume r= 2 QT At (A, = area of shaded portion in Fig. 5 )

where

5 z=~ elevation in metres,

T - time in seconds, and

QLT = discharge in tunnel in m”/sec.

Keeping factor of safety as 2, the volume of expansion gallery is fixed as twice the volume calculated by the above formula for the preliminary analysis.

6.2 After finding out the volume, dimensions ( see Fig. 1A ) of the expansion ( chambers )

galleries are tentatively fixed and the

analysis (preferably with the computer) is made to check the fixed dimensions so that the water level in the surge tank does not exceed the fixed level A as shown in Fig. 2.

7 TENTATIVE VOLUME OF LOWER EXPANSION GALLERIES/CHAMBERS

7.1 The procedure given in 6.1 and 6.2 shall be followed.

8 ANALYSIS

8.1 Upper Expansion Gallery

When the necessity of expansion gallery is established the difference between the height of maximum water level calculated under 5.1.1 and 5.1.2 is found out.

8.1.1 Shape

The shape of upper expansion gallery should preferably be D-shaped.

8.1.2 Size

Area of the expansion gallery/galleries should be determined on the basis of discharge and generally height should be more than the width of the gallery.

IS 7396 ( Part 3) : 1990

Indian Standard

CRITERIA FOR HYDRAULIC DESIGN OF SURGE TANKS

PART 3 SPECIAL SURGE TANKS

1

IS 7396 ( Part 3 ) : 1990

8.1.3 Layout of Upper Galleries

Typical layout of galleries is shown in Fig. 1 and 3.

The gallery/galleries may be connected with surge tank with its roof level generally at/below the maximum water level determined in accordance with 5.1.1.

8.1.4 Slope

Slope of the gallery should not be less than 1 in 150 as shown in Fig. 1 in order to empty out the gallery efficiently.

8.2 Lower Expansion Gallery

8.2.1 Shape

The shape of lower expansion gallery should

preferably be D-shaped.

8.2.2 Size

The area of lower expansion gallery/galleries shall be in accordance with 8.1.2.

8.2.3 Slope

Slopes shall not be flatter than 1 in 150 as shown in Fig. 1.

8.2.4 Layout of Lower Galleries

Typical layout of galleries is shown in Fig. 1 and 3.

The gallery/galleries may be connected with the surge tank with its bottom level generally at/ above the minimum water level determined in accordance with 5.1.1.

IS 7396 ( Part 3 1 : 1990

MAXIMUM WATER LEVEL ----c AIR VELT

UPPER EXPANSION GALLERY

SLOPE 1 IN lso . LOWER

MINIMUM WATER LEVEL

EXPANSION GALLERY/

SLOPE 1 IN 150 __-_ -_--_ m--v

-AT -Q T

A ,, = AREA OF TUNNEL

As = AREA OF SURGE TANK

1A

MAX WATER LEVEL

UPPER EXPANS_ION GALLERY

SLOPE 1 IN 150-

HiN WATER LEVEL> SLOPE 1 IN 150 _

---- J z ---_' SLOPE 1 IN 150

LOWER EXPANSION GALLERY

1B

FIG. 1 TYPICAL TYPES OF SURGE TANK WITH EXPANSION GALLERY

3

IS 7396(Part3):1!HO

RESERVOIR

MWL P-. _-

LwL.Y-.

SURGE TANRz

G c.7---------

-- --

-52

X -:--------

--- ---_ .

X

4 4

._-

--_

e-v

VM --_

.-- v‘ WI

_s

---

-_-

1 r

NOTES A = Maximum water level as per the turbine characteristics

B = Minimum water level as per the turbine characteristics

C & D = Maximum & minimum water level ( scc 5.1.2 )

E & F = Minimum & maximum water level at the draw-down condition

G & H = Maximum & minimum water level in the reservoir

FIG. 2 SURGE TANK ACCORDING TO TURBINE CHARACTERISTICS

WHlU?4 WATER LEVEL -_---__ ----__ A_^ --

\J 5

1 SL4M'E 1 IN.150

RETAINING WAU.

ffIN WATER LEVEL L EXPANSION GALLERY

-----_ APPROACH TuwtlEL a---

b

As = AREA OF SURGE TAM

AT -AREAOFTUNNF&

FIG. 3 SURGE TANK WITH PART OF APPROACH TUNNEL AS EXPANSION GALLERY

4

IS 7396 ( Part 3 ) : 1990

60

t

44

20

2 0

-20

-40

-60

-80

LEVEL A OF Fig. 2

FULL RESFRVOIR

-T

SCALE

HS: 1 cm = 20 seconds -VS: 1 cm = 6.1 m

l-h. 4 ELEVATION AND TIME RELATIONSHIP

LEVEL

SCALE

HS: 1 cm = 20 secqnds

vs:1ca= . 28 34r&sec)

FIG. 5 DISCHARGE AND TIME RELATIONSHIP

5

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