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IS 12967-1 (1990): Analysis of hydraulic transients inhydro-electric and pumping plants - Code of practice, Part1: Criteria for analysis [WRD 14: Water Conductor Systems]

IS 12967 ( Part 1) : 1990

Indian Standard

ANALYSISOFHYDRAULICTRANSIENTS INHYDRO-ELECTRICANDPUMPING ..C

PLANTS-CODEOFPRACTICE PART 1 CRITERIA FOR ANALYSIS

UDC 627’844 : 620’162’4 : 621’311’21

. . .

/-\ 4 \ :

._’ @ BIS 1991

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

NEW DELHI 110002

Junua~ 1991 Price Group 2

Water Conductor Systems Sectional Committee, RVD 14

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards on 20 March 1990, after the draft finalized by the Water Conductor Systems Sectional Committee had been approved by the River Valley Projects Division Council.

The hydraulic transients are caused due to unsteady discharges resulting from operation of hydroelectric and pumping plants. The hydraulic transients may be .caused both during normal or emergency conditions of operation. There are various devices to reduce or eliminate undesirable transients and it shall be selected after careful study of different alternatives.

IS 12967 ( Part 1) : 1990

Indian Standard

ANALYSIS OF HYDRAULIC TRANSIENTS IN HYDRO-ELECTRIC AND PUMPING

PLANTS -CODE OF PRACTICE PART 1 CRITERIA FOR ANALYSIS

1 SCOPE

1.1 This code deals with the hydraulic transient in closed conduits of a Hydro-Electric Plant and discharge line of pumping plant.

2 TERMINOLOGY

2.0 For the purpose of this standard the follow- ing definition shall apply.

2.1 Hydraulic Transient

In a closed conduit, when the flow is unsteady that is the discharge at each section is varying rapidly from one instant to the next, rapid pressure changes occur inside the conduit. Such pressure changes caused by rapid flow changes are termed as hydraulic transient.

3 CAUSES OF TRANSIENTS

3.1 Turbine - Penstock Installation

The following operations produce transient conditions in a turbine penstock installation:

a) Unit Synchronized to a Large System

i) Load acceptance

ii) Load reduction or total load rejection

b) Isolated Unit

i) Unit start up

ii) Load acceptance

iii) Load reduction or total load rejection

C) Hydraulic transients produced by resonance due to the vibration of runner blade and guide vanes, leakage from valve seal and governor hunting.

3.2 Pumping Installation

The following operations produce transient state conditions in the discharge line of pumping installations:

a) Opening, closing or chattering of valves in a pipe-line;

b)

4

d)

Starting and stopping the pumps in a pumping system;

Stoppage of pumps due to sudden power failure; and

Resonance caused by leakage from valves, vibration of guide vanes.

4 DATA

4.1 For calculation of hydraulic transient in a turbine penstock installation and pumping installation, data required is as follows:

a) Turbine Penstock Installations

i)

ii)

iii)

iv)

v)

vi)

Details of water conductor system such as profile length, shape, material of conduit and size of conduits;

Type, location and characteristics of protective devices such as surge tank and pressure relief valves;

Type of turbine and turbine characteristics;

Generator characteristics like torque, inertia and efficiency;

Type of governor and its characteristics; and

Design discharge and head on turbine.

b) Pumping Installation

i) Details of discharge line, such as, profile, length, shape and size of pipe line including location;

ii) Type, location and characteristics of protection devices on pipe line such as surge tanks, air chamber, valves, etc;

iii) Pump characteristics; and

iv) Design discharge and pumping head.

5 OPERATIONAL REQUIREMENTS

5.1 Following are some of the constraints set by operational requirements for the calculation of hydraulic transients in turbine-penstock installation and pumping installation. *

IS 12967 ( Part 1 ) : 1990

5.2 Turbine - Penstock Installation 4

5.2.1 The maximum reduction in electrical power output that can result from circuit breaker operation.

5.2.2 The maximum allowable speed rise in the turbine fed by any one penstock. e)

5.2.3 The maximum rates of load change that generating plant is required to accommodate to satisfy system requirements.

5.2.4 Limitations set over the range of variation of transient pressures.

5.3 Pumping Installation

5.3.1 The maximum reduction in power input that can result from electrical faults.

5.3.2 Limitation set on the magnitude and rate of variation of discharge.

5.3.3 Limitation set on reverse rotation of pumps.

5.3.4 Limitation set on the column separation in pipe lines.

6’ OPERATING CONDITIONS

formation of

6.1 The pressure rise due to hydraulic transient conditions in a turbine penstock installations and pumping installations are considered for the following conditions.

6.2 Turbine - Penstock Installation

6.2.1 Normal Operating Condition

The design criteria for dynamic pressure rise or drop due to water hammer under normal operating conditions shall be due to full load rejection or specified acceptance. The basic conditions to be considered as normal operations are as follows:

a>

b)

4

The turbine-penstock installation may be operated at any head between the maximum and minimum water levels in the reservoir or forebay or surge tank;

The turbines may be operating at any gate position and be required to drop any or all of the load;

Where the turbine-penstock installation is equipped with any of the pressure control devices like surge tanks, relief valves, governor control device and cushioning stroke device, it is assumed that these devices are properly adjusted and function in the manner as contemplated in the design;

Unless the actual turbine characteristics are known the effective flow area through the turbine gates or nozzles during maximum rate of gate movement may be assumed to be linear with respect to time;

The turbine gates may be moved at any rate of travel by the action of the governor head up to a predetermined rate or at a slower rate by manual control through auxiliary relays. The water hammer effects may be computed on the basis of governor rate which is set by the governor relay valve stops for speed regulation;

,

The penstock alignment shall be checked such that due to load acceptance water column separation shall not cause a penstock failure due to collapse; and

When the closure is set at a slow rate, the water hammer caused by runaway when full load discharge reduces to runaway discharge during the speed rise shall be considered.

6.1.2 Emergency Condition of Operation

For emergency condition of operation the dynamic pressure rise is due to sudden load rejection. The basic conditions to be considered as emergency operation for an impulse and reaction turbine is as follows:

a) Impulse turbine

The dynamic pressure rise due to needle slam on loss of oil pressure or mechanical failure. As the needles are hydraulically balanced at mid-point, the turbine flow cut-off shall be taken as instantaneous due to slam closure of of the needles from half position.

b) Reaction turbine

i) The turbine gates may be closed at any time by the action of the governor head, manual control of the main relay valve or by the emergency selenoid device. The gate traversing time will be taken as the minimum time for which the governor is designed;

ii) Cushioning stroke or pressure relief valve if present, shall be assumed to be inoperative in one unit; and

iii) The water hammer shall be computed for the maximum reservoir head condition for final part gate closure to zero gate position on one unit at the

maximum governor rate of*seconds. a

9

2

6.2 Pumping Installation

6.2.1 Normal Conditions of Operation

i)

ii)

iii)

iv)

v)

vi)

Pumps may be started or tripped manually or automatically throughout the entire range of pumping heads specified for the installation;

If there is more than one pump on the line, all are tripped simultaneously, however, only one may be started;

Where the pump discharge system is equipped with any of the pressure control devices like surge tanks, air chambers;

If a check valve is present in the discharge line, the hydraulic transients will be computed on the basis that the check valves close immediately upon the reversal of flow;

If an air chamber is present in the pump discharge line system, it is assumed to have a minimum air volume during the power failure; and

The alignment of the pump discharge line shall be checked to see that water column separation does not occur at any point, due to power failure.

6.2.2 Emergency Conditions of Operation

i>

ii)

iii)

iv)

If surge suppressors, surge tanks or pressure relief valves are present only one will be assumed to be inoperative;

Closure of one of the check valves provided for shutting off return flow through the pumps is delayed and occurs at the time of maximum reverse flow;

Air-inlet valves, if present in the system are assumed to be inoperative; and

Power failure occurs at any time during or following the starting of a pump or pumps.

7 FACTOR OF SAFETY

7.1 Turbine-Penstock Installation

The minimum factor of safety to be adopted for the design of turbine penstock, surge tank and other pressure control devices to withstand normal and emergency condition of operation

IS 12967 ( Part 1) : 1990

shall be as follows:

Conditions of Operation Factor of Safe&

a) Normal ( one unit ) 2’0

b) Normal ( more than 1’6 one unit)

c) Emergency 1’25

7.2 The factor of safety is based on the yield point stress of steel pipe lines, turbine or pump casing. The factor of safety for specials like bifurcation is increased by 125 percent.

8 DEVICES FOR CONTROLLING TRANSIENTS

8.1 The devices commonly used to reduce or to eliminate the undesirable transients such as excessive pressure, column separation and pump or turbine over speed following a power failure or load rejection are following:

i) Surge tanks;

ii) Air chamber; and

iii) Valves such as safety valves, pressure relief valve, pressure regulating valve, air inlet valves, check valves and bursting disc.

8.2 Surge tank and pressure relief valves are used on a turbine penstock installation to control pressure rise due to hydraulic transient. On a pumping installation all the devices mentioned above are used together or in combination.

8.3 The severity of undesirable transients can also be reduced by any of the following methods:

a) b) 4 d)

4

f)

By changing profile of pipeline;

By increasing diameter of pipeline;

By reducing water hammer wave velocity;

Use of check valves downstream of pumps;

NOTE-Wave velocity depends on elastic parameters and also conduit size, wall thickness and wall material and also external constraints such as type of support and freedom of longitudinal movement of conduit.

The rotation inertia of turbine or pump and of generator or motor mechanically coupled to turbine or pumps.

Dual closing of guidance servomotors.

8.4 The choice and type of controlling devices to be used shall be decided by various alternative studies. The alternative that gives an acceptable system response as defined by operation requirement and overall economical system shall be selected.

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Dot : No RVD 14 ( 4660 )

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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