9-EEE - IJEEER - HYDRO POWER - R Krishna Kumar

HYDRO POWER GENERATION FROM DOMESTIC WATER SUPPLY

SYSTEM AND DEVELOPMENT OF DYNAMIC FLOW MODELLING 1R. KRISHNA KUMAR & 2S. IAN DAVID

1Asst.Professor(Sr.Grade), Dept. of EEE, PSG College of Technology,Coimbatore , TamilNadu , India

2Department of EEE, PSG College of Technology,Coimbatore, TamilNadu , India

ABSTRACT

Pico hydro is a term used for hydroelectric power installations that typically produce up to 5 kW

of electricity. It was regarded as an alternative generation source in recent past. Traditionally

hydroelectric power was generated from flowing and run off water in mountain streams and big

reservoirs. Pico hydro power plant is installed where, only low heads are available (less than 15 m) but

the flow rate must be greater to compensate for the lower water pressure. This paper deals with a

comprehensive renewable energy system, where untapped decentralized water potential such as drinking

water tanks which has sustainable supply of water will be utilized to produce electricity. It describes

hydro graph, supply pattern, plumbing method practiced in typical drinking water tower and the turbine

design that would suit Pico hydro power generation from drinking water reservoirs. It also discusses the

effect of pressure in the terminal outlets in the existing systems. The field studies carried out at the

secondary reservoir at Singanallur, Coimbatore and secondary storage tank at Peelamedu, Coimbatore

are presented. Results from the field study emphasize that the proposed system is feasible enough for

electricity generation and indicate the prospect of further improvement and future research.

KEYWORDS : Archimedes Screw Turbine, Domestic Drinking Water, Pico-Hydro Electricity, PM

Generators, Renewable Energy.

INTRODUCTION

The electricity, not only a vital element for community development but has become one of the

basic need for human life. Hence there is an increasing need to generate electricity from all available

resources. Among various other renewable resources hydro electricity is more reliable and robust. Pico

hydro is a term used for hydroelectric power installations that typically produce less than 5 kW of

electricity, usually using run-off water from streams and lakes in rural areas. But water distributed to

residential area from secondary reservoirs also has the potential for generation of electricity.

In this paper newly designed hydro power system suited for domestic drinking water pipeline

based on field data collected at secondary storage reservoirs at, Coimbatore is proposed.

International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN 2250-155X Vol.2, Issue 3 Sep 2012 94-105 © TJPRC Pvt. Ltd.,

95 Hydro Power Generation from Domestic Water Supply System and Development of Dynamic Flow Modelling

WATER DISTRIBUTION

Drinking water to Coimbatore city residents is supplied from Pillur –Aathikadavu plant. The

water passes through various purification processes. From the purification plant purified water is sent to

primary reservoirs .Water from primary reservoirs is taken through a complex series of pipes for

delivery to homes and businesses. As a result of this there is continuous inflow of water to the reservoirs

throughout the day for the whole year. It is estimated that an average person consumes about 135 liters of

water per day. The cyclic rotation pattern with duration of 8 hours per street is followed for water

distribution. Hence there is a continuous outflow in the common discharge tube from the reservoir.

Fig:1 Water Distribution Methodology

HYDRO ELECTRICITY

Hydro electricity is generation of electricity from moving water sources by harnessing the

potential and kinetic energy using available head and flow. Hydro power plants are usually found in rural

and hilly areas. Also drinking water distributed to residential areas from the secondary reservoirs also

has excess pressure head and drinking water being basic need, there will be continous flow all round the

year.Hence the secondary storage reservoirs can provide potential sites for Pico-hydro power plants.

PROPOSED METHODOLOGY

In this hydro power system the excess pressure from the flow of water will be harnessedr

without disturbing the distribution flow parameters.When the water passes through the turbine(smooth

turbine surface) the velocity of flow nor flo rate is affected,only the Reynolds number Re (a

dimensionless number that gives a measure of the ratio of inertial forces to viscous forces) changes i.e

the flow changes to turbulent flow. This makes it feasible to be placed in the existing drinking water

supply system.

R. Krishna Kumar & S. Ian David 96

Fig:2 Proposed Methodology

POSITION OF TURBINE

The turbine will be placed at the bottom of the common discharge tube before the bifurcation of

the outflow pipe for distribution to various streets. The turbine is placed in an optimum position to

harness the excessive pressure and the available flow rate .The excess water pressure and flow required

according to standards are the major parameters that determine the position of turbines.

Fig:3 Position of Turbine

Turbine

Common Discharge Tube


TURBINE SELECTION

The availability of head is less than 15 meters and flow rate is around (50-300)

L/sThe key design parameters for a turbine are head (H), volume flow, or discharge (Q) and rotational

speed (N).

From these three parameters, a “dimensionless shape number” or “specific speed” can be determined.

This number gives an indication of the geometry of the turbine and it is the starting point for detailed

design.

For this design procedure we use the following equation:

Specific speed (Ns) = (N√P)/ H5/4

Where P is Power in kW, N is in rpm, Q in m3/s and H in m. The two primary classification of water

turbines impulse turbine or reaction turbines .In addition to these two there is a new type of turbine called

Archimedes Screw turbines.

Type of

Turbine

High

Head

Medium

Head Low Head

Impulse

Turbine

Pelton

Turgo

Cross flow

Multi jet

Pelton Turgo

Crossflow

Reaction

Turbine -- Francis

Kaplan

Archimedes

Screw

The Archimedes screw turbine is closer to the reaction turbine in that the weight of falling water

turns the screw to generate power. The water enters the screw at the top and the weight of the water

pushes on the helical flights, allowing the water to fall to the lower level and causing the screw to rotate.

This rotational energy can then be extracted by an electrical generator connected to the main shaft of the

screw.


Fig :4 Archimedes Screw

Archimedes Screw type turbines are especially suited to sites with high flows (200 litres/sec to

6000 litres/second) and work economically with head levels from 1 to 10 meters. The smallest screws are

just .75 meter diameter and can pass 250 liters / second, then they increase in 250 mm steps all of the

way up to 5 meters in diameter with a maximum flow rate of around 14.5 m3/s

Archimedean screws typically rotate at around 26 rpm, so the top of the screw connects to a

gearbox to increase the rotational speed to between 750 and 1500 rpm to make it compatible with

standard generators. Even tough they rotate relatively slowly Archimedean screws can splash water

around, though this is reduced significantly by the use of a splash guard

Archimedean screws are normally set at an angle of 22 degrees from horizontal, which is the

optimum for the most cost-effective installations.

Fig:5 Efficiency(Mechanical) Vs % Flow rate

They are technically very simple with significantly lower installed costs than comparable low

head Kaplan turbines.


A very flat efficiency curve which means that even dramatic changes in flow levels or head levels do not

significantly impact the efficiency of the system (and without the mechanically adjustable blades of a

Kaplan turbine).

Ruggedness – Because the design and construction is so simple, because the design is so

tolerant of trash, etc. Archimedes screw type systems are extremely robust and can be expected to last

40 years or more with a minimum of maintenance.

PERMANENT MAGNET GENERATOR

The generators used in major hydro power generating stations employs electromagnetic field

systems. But the generator used here is of permanent magnet type. The generator has two magnetic

components: the rotating magnetic field constructed using permanent magnets; and the stationary

armature constructed using electrical windings located in a slotted iron core. Fig.6 shows the

construction of a typical PM generator in a cross sectional view.

Fig :6 Permanent Magnet Rotor

The PM’s are made using high-energy rare earth materials such as Neodymium Iron Boron or

Samarium Cobalt. Retention of the PM”S on the shaft is provided by high strength metallic or composite

containment ring. The stationary iron core is made of laminated electrical grade steel. Electrical windings

are made from high purity copper conductors insulated from one another and from the iron core. The

entire armature assembly is impregnated using high temperature resin or epoxy.

The voltage output from the generator is unregulated AC. This voltage varies as a function of

the speed of generator.

MODELLING OF WATER COLUMN

The turbine is to be placed in the drinking water discharge tube at secondary reservoirs(water

towers or water tanks).

Modelling is done by assuming water to be an incompressible fluid and the discharge

tube(Penstock) is a rigid conduit

From the laws of momontum,the rate of change of flow in the discharge tube is


(p0-p-pf) ...(1)

Where

Q= Flow rate at turbine

Tw=Characteristic constant of Water Discharge tube called Water Time constant or Water starting time.

p0=Static pressure of the water column

p=pressure at turbine

pf=Pressure loss due to friction in Water Discharge tube

The friction pressure loss is calculated as flow squared.

Pf=fpQ2 ...(2)

MODELLING OF TURBINE

The turbine characteristics depend on Gate position

Q=Gp …(3)

Wher G-function of Gate position.

MODELLING OF THE DISCHARGE TUBE(CONDUIT)

The flow dynamics in the common discharge tube is given by(4),

Twc = p0c - pc - fc Q2 ...(4)

Where,

Twc=Water time constant of common discharge tube

fc=friction coefficient of common discharge tube

pc = pressure at the Turbine between the common tunnel and the individual penstocks.

P0c = static pressure of the water column at the turbine

The flow dynamics in the discharge tube in ith street without the turbine is given by(5),

Twi ( p0i - poc )-( pi - pc )- fpi Q2 ...(5)

Where,

Twi=Water time constant of common discharge tube in ith street

fpi=friction coefficient of discharge tubein ith street

Qi = flow in discharge tube in ith street


poi = static pressure at the discharge tubein

ith street

pi = pressure at the tube in ith street

The flow dynamics in the common discharge tube after the turbine is placed is given by(6),

Twi ( p0i - pi )-Twc - fpi Qi 2- fc Q2-Pturbine

…(6)

Qc = flow in the common conduit (forced to be equal to the sum of the flows in the individual penstocks,

by the continuity equation)

Pturbine = pressure loss due to turbine

Thus eqn(6) explains the loss of flow due to placement of turbine in the discharge tube.

PLUMBING

Steel Pipes are extensively used for water supply. They are best suitable for long distance

domestic water distribution. Mostly grid type of plumbing method is used to interconnect the adjacent

streets.The pipes are kept vertically at 90 degrees but for Archimedean screws are normally set at an

angle of 22 degrees from horizontal, which is the optimum for the most cost-effective installations.

Hence the pipes should be inclined at least 22 degrees.

HYDRO POWER(Ep)

Hydro power is that power derived from the force or energy of moving water,which may be

harnessed for useful purposes such as generating Electricity. It is given as

Ep=mgH ….. (7)

Where

Ep=Potential Energy Of Water(J)

m=Mass of water(kg)

g=Accaleration due to gravity(m/s2)

H=Gross water head(m)

MECHANICAL POWER (P)

The mechanical power output of turbine is

P=gρQH ……. (8)


Where

P=Hydro power output(W)

ρ=Density of water (1,000 kg/m3)

Q=Flow rate(m3/s)

ENERGY OUTPUT

The Energy output of the generator is given by

W=P*η*t ...(9)

= gρQH* η*t

=9.81 *1000*QH* η*t

=9.81*QH* η*t kWh

Where

t=Operation duration(time)(8,760h/year)

η=Overall Efficiency (50-90%)

The equation to calculate flow rate of water is.,

Q=Av ...(10)

Q=Flow rate(m3/s)

A=Average Cross-sectional area of discharge tube (m2)

v=surface velocity(m/s)

CASE STUDY I

Fig:7 Secondary reservoir at Singanallur, Coimbatore.

The secondary reservoir at Singanallur has a capacity of 10 Lakh litres. The height of the tank

is 14 meters. There is continuous inflow and outflow occurring all throughout the day. The outflow rate


is 69.44 L/s. The water flow from the reservoir varies from time to time for a given day. The graph below

shows variation of flow rate as a proportion of maximum flow rate (69.44 L/s). The water is distributed

to the household by the force of gravity only.Hence there is an average flow rate of 55.552 L/s

throughout the day.

Fig:8 Variation Of Flow rate in a Day

The reservoir in the tower should have a minimum height of approximately 6 meters (20 ft) and

a minimum of 4 m (13 ft) in diameter to supply water to the household. The water pressure available at

the household terminals is more than the required standards for household domestic water supply.There

has also been some instances of having excessive water pressure which has lead to water main breaks

and leaks. Excess pressure release valves have been installed to reduce pressure.

From the field data ,

With available head of 12.5meters

Average flow rate of 55.552 litres/s

The Net hydro power available is

Ep = 9.8*1000*12.5

=122500 (watts)

With a conversion efficiency of 50% ,

The Electric power output(estimated value),

P=9.8*1000*12.5*55.552*0.5(efficiency)

=3402.56 (watts)


CASE STUDY II (PEELAMEDU, COIMBATORE)

The secondary reservoir at Peelamedu has a capacity of 15 Lakh liters. The height of the tank is

15 meters. There is continuous inflow and outflow simultaneously throughout the day. The average

outflow rate is 283.33 L/s. The water flow from the reservoir varies from time to time for a given day.

The graph below shows variation of flow rate as a proportion of maximum flow rate (294.16 L/s). The

water is distributed to the household by the force of gravity only.Hence there is an average flow rate of

283.33 L/s throughout the day.

Fig:9 Variation Of Flow rate in a Day

From the field data ,

With available head of 15 meters

Average flow rate of 283.33 litres/s

The Net hydro power available is

Ep = 9.8*1000*15

=147 kW

With a conversion efficiency of 50% ,

The Electric power output(estimated value),

P=9.8*1000*15*283.33*0.5(eff)/1000

=20.825kW

CONCLUSIONS

Hence there is huge potential for implementation of hydro power system at the secondary

reservoirs for drinking water. The excess pressure of the main pipeline water supply, that representing

the head (falling water), and the water supply flow rate are the main determining factors for this hydro


electric system. The conversion efficiency can be improved by using Permanent Magnet AC generator

and other circuitry.

REFERENCES

1. E. De Jaeger, N. Janssens, B. Malfliet , F. Van De Meulebroeke ,“Hydro turbine model for

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“Investigation on the performance of Pico-hydro generation system using consuming water

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operation and management APSCOM 2009, Hong Kong, China, Nov 2009, ISBN

9781849192149

3. IEEE Working Group on Prime Mover and Energy Supply Models for System Dynamic

Performance Studies "Hydraulic turbine and turbine control models for system dynamic studies"

IEEE Trans. on Power Systems, Vol. 7, No. 1 (Feb. 1992), pp. 167- 179

4. R.Ramkumar,“Renewable Energy Resources and Developing Countries”, IEEE transactions on

power apparatus and systems, Vol. PAS-102, No. 2, Feb.-1983, pp-502-510.

5. A Harvey & A Brow, “Micro-hydro Design Manual”, ITDG Publishing, 1992.

6. J.B.Gupta,“A course on power systems” 10th Edition 2010-2011, S.K Kataria & Sons

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induction generator,” IEEE Trans. Energy Conversion, Vol. 12, pp. 109-117, June 1997.

8. http://en.wikipedia.org/wiki/Pico_hydro

9. http://www.arch.hku.hk

10. http://pumpandgenerator.com/water-pump-turbine-generator/

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9-EEE - IJEEER - HYDRO POWER - R Krishna Kumar