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

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

HYDRO POWER GENERATION FROM DOMESTIC WATER SUPPLY SYSTEM AND DEVELOPMENT OF DYNAMIC FLOW MODELLING 1

R. KRISHNA KUMAR & 2S. IAN DAVID

1

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

2

Department 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.

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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.

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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.

Common Discharge Tube Turbine

Fig:3 Position of Turbine

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

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

High

Turbine

Head Head

Impulse Pelton Turbine

Turgo

Medium

Low Head

Cross flow Multi jet

Crossflow

Pelton Turgo Kaplan

Reaction Turbine

--

Francis

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.

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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.

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

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

R. Krishna Kumar & S. Ian David

100

(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=Gďƒ–p

‌(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 Q i = flow in discharge tube in ith street

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

poi

=

static

pressure

at

the

discharge

tubein

th

i 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),

T wi

( p0i - pi )-Twc

- fpi Q i 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)

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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

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

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)

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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

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

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

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E. De Jaeger, N. Janssens, B. Malfliet , F. Van De Meulebroeke ,“Hydro turbine model for system dynamic studies” IEEE Transactions on power systems Vol .9, No. 4, Nov 1994.

2.

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Nov 2009,

ISBN

9781849192149 3.

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4.

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5.

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

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Edition 2010-2011,

S.K Kataria & Sons

Publication.

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8.

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

9.

http://www.arch.hku.hk

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