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Abstract

This paper reviews the current research works on the end suction centrifugal pump coupled with induction generator running in turbine mode for microhydro application. The information can be used by practicing engineers, researchers, and plant managers to understand the potential of pump running as turbine. Review on experimental and simulation works was carried out encompassing end suction single stage low specific speed which is less than 10 kW. This is followed by review of their efficiency improvement through modifications. The results show that centrifugal pump can operate in turbine modes without any modification on mechanical components. However, to achieve the best efficiency point (BEP), it requires higher flow rate and head than pumping rating. Efficiency improvement is viable through geometric modification to improve hydraulic characteristic. The studies also show that pump as turbine (PAT) can be directly coupled with modified induction motor as generator by adding capacitor and electric control system, regulating voltage and frequency at the output terminal. It was found that PAT offers the best low cost solution for microhydro application especially for third world countries that do not have local microhydro manufacturer.

1. Introduction

Hydropower is a well-known renewable energy source generating clean, secure, and predictable electric power. It has zero carbon emission, low operational cost, and virtually zero greenhouse gas emission. With the technology of over one hundred years, hydropower is considered as the most established technology to provide energy in a small or large scale. By far, hydropower is the largest renewable energy produced accounting for 90% of the total renewable energy worldwide [1]. In 2010, hydropower has been utilized in 150 countries with installed capacity of 860 GW and Europe having the highest installed capacity followed by East Asia and Oceania [2].

While large hydropower plants feed the national grid, typical off-grid microhydro is the most popular solution for electrification among rural communities which supplies power in the range of 5–100 kW which usually use a run-of-the-river to divert some of the water from the river before dropping into a pressurized penstock. The water potential energy from the gravitational force over height difference is converted to rotational mechanical energy. A hydro turbine is used to transform energy from the flowing water to mechanical rotational energy and then a generator transforms the rotational mechanical energy to electrical energy regulated by electric control system. Microhydro configurations vary depending on the topography and hydrological site conditions [3].

The main components that comprise typical microhydro schemes are electromechanical equipments, civil structures, and energy distribution systems [4]. An optimum operational design, smart selection of equipment, and reduced professional consultation input can lower the overall cost [5 –7]. It is important to pay attention to actions to reduce the whole microhydro cost because it is always the main concern for small communities especially in rural areas. In order to minimize the overall cost, microhydro system must be in the optimal operation and component selection. Furthermore, the microhydro must be reliable, robust, and manageable with minimum technical knowledge by local communities.

2. Pump as Turbine (PAT)

The electromechanical unit is one of the most expensive components in microhydro system. Generally, microhydro manufacturers offer high efficiency turbine performance; however, they are expensive and unaffordable particularly for rural communities. The use of PAT for microhydro offers low cost solution as a substitution for commercial microhydro turbine. Domestic and industrial end suction centrifugal pumps cover a wide range of flow and head are readily available and mass produced in many countries. The advantages of PAT compared to commercial turbines are simple constructions, know-how knowledge which is readily available, and low operating and initial cost thus making the technology more affordable, and these advantages are the reasons why there are a large number of PATs installed in rural areas [8, 9].

Pump as turbine (PAT) as an unconventional type of turbine does not have a flow regulating mechanism; therefore, each pump running in the turbine mode has single best efficient point (BEP), in which the flow rate and head are fixed for a particular point. The application of PAT is suitable for radial and mixed flow serving low specific speed turbine which is normally covered by a single jet Pelton wheel, multijet Pelton wheel, and crossflow turbine in the range of 13 to 100 m of head [10 –12] as shown in Figure 1. Axial flow pumps which are not covered in this paper are prone to cavitation and are more expensive; thus they reduce the cost-benefit factors.

Figure 1:

Range of application for different PAT for hydropower [12, 44, 45].

3. Research Review

3.1. Experimental Analysis of PAT

Pump manufacturers only supply pump mode performance curve and this makes it difficult to predict the turbine mode performance. Many attempts have been made to predict turbine mode performance by using analytical model but the percentage of deviation is relatively large compared to the actual performance [13 –16]. To attain a definite characteristic pump in turbine mode, the pump is required to be tested over a range of heads and flows shown in Figure 2. A feed pump producing greater head and flow is used to supply inverse flow to the studied pump. The characteristic can be obtained at constant rotational speed controlled by electrical control equipment. The review on present PAT experimental works is presented in the following.

Figure 2:

Laboratory schematic test rig for PAT.

Derakhshan and Nourbakhsh (2008) had tested four industrial centrifugal pumps with specific speed between 14 and 60 (m,m³/s) to derive a prediction model for the best efficient point based on pump hydraulic characteristic [16]. The test showed that centrifugal pump can operate in turbine mode without mechanical problem. Based on the experimental data, all centrifugal pumps give lower BEP running in turbine mode compared to pump mode. The efficiency in turbine mode was reported to be between 60 and 80%. The authors suggested that bigger pump impeller performs better in turbine mode.

Raman et al. (2013) had carried out experimental investigation of a centrifugal pump with specific speed of 15.36 working in turbine mode [17]. Calgon (HES 40–200) end suction centrifugal pump with head and flow of 22 m and 8.31 l/s was used for the test. 5 kW, 230 V synchronous AC generator was directly coupled to the pump. Control panel measured the rotational speed, generator voltage, current, and frequency of the system. The experiment shows that the best efficient point (BEP) was found at higher head and flow than in the pump mode. The efficiency was recorded at 39%, head and flow of 30 m and 13.52 l/s, respectively. The efficiency in pump mode was reported at 59% and the lower efficiency suggests higher hydraulic loss in the turbine mode.

Fernández et al. (2004) presented a performance study of a centrifugal pump in order to justify the feasibility of using pump in turbine mode by determining pump and turbine performance and radial thrust and prediction of pump-turbine characteristic curves [18]. The pump used for the study had a single axial suction and spiral volute casing with an impeller of 200 mm. The pump was tested using hydraulic setup standard ISO3555:1977. The best efficiency point in turbine mode was reported at 58% corresponding to flow coefficient and head coefficient of 0.015 and 0.011, respectively.

Nautiyal et al. (2011) studied the performance characteristics of a centrifugal pump running in pump and turbine mode. A Kirloskar (KC100-65-315) pump with specific speed of 18 was selected for the test [19]. The pump ratings for head, flow, and power are 32.8 meter, 14.8 l/s, and 8.18 kW, respectively. A synchronous generator of 12.5 kVA was coupled to the pump to measure power output running at 1500 rpm. The efficiency of pump operating in turbine mode was found to be 8.53% lower than the best efficiency in pump mode.

3.2. Numerical Analysis on PAT

The computer fluid dynamic (CFD) analysis provides great tools in the designing and performance analysis of fluid dynamics in turbo machinery. This tool allows researchers, engineers, and plant managers to test hydraulic performance in virtual condition. With the advancement in numerical algorithms and computing power, CFD plays a significantly large role in the discipline of fluid dynamics and turbo machinery. CFD allows various parameters investigation such as flow visualization, hydraulic optimization, off-design operation, and cavitation analysis which are impossible to perform by experimental work. Moreover, CFD can provide a pinpoint insight for local flow phenomenon and allow for the alteration on corresponding parameters for optimization purpose. An example of PAT computer design model is shown in Figure 3.

Figure 3:

PAT computer aided design model.

Natanasabapathi and Kshirsagar (2004) had conducted a simulation study on PAT using ANSYS CFX (V5.6) on newly developed unstructured mesh geometry replacing complex blocked mesh [20]. Unstructured mesh was used to match the pump complex geometry. The flow domain was divided into three individual parts as casing, runner, and draft tube. Total pressure boundary condition and average static pressure were set at the inlet and outlet, respectively. Comparison between experimental data and simulation shows good agreement for head drop across the turbine; however, there was a deviation in the efficiency for discharge. Further enhancement by additional interface ring between the casing and runner leads to considerably reduced error.

Yang et al. (2012) presented a computational fluid dynamics analysis on reverse mode performance prediction using commercial flow solver, ANSYS-CFX software [21]. The control volumes domains were divided into five component parts: inlet pipe, front, back chambers, impeller, and volutes. Each part used different types of mesh, tailored to suit flow pattern and requirements. Structured hexahedral grid was used to generate meshes for each individual component. Comparison of experimental and simulation results shows that both performance curves are in good agreement. The relative error between both results at BEP for efficiency, head, and power is −3.02%, −0.78%, and −0.78%, respectively. The study highlighted the importance to establish performance prediction model using theoretical analysis, empirical correlation, and simulation results.

Fernández et al. (2004) investigated three-dimensional flow simulation for end suction centrifugal pump installed with an impeller size of 200 mm operating in turbine mode by using commercial Fluent software [18]. Specially refined mesh was used at critical flow domain in the pump such as leading and trailing edges of the impeller and volute tongue. Uniform velocity distribution was set at the inlet and constant static pressure at the outlet. Turbulence effect of standard k-epsilon was used together with standard wall function. Good agreement and trend between numerical computation prediction and experimental analysis were observed. However, the numerical analysis yielded higher performance as predicted. The reason can be explained by leakage loss that was excluded in the simulation work. Once validated, the simulation model was later used to investigate hydraulic flow and radial force.

Rawal and Kshirsagar (2007) conducted numerical simulation on a single stage, mixed flow pump having an impeller size of 236 mm operating in turbine mode [22]. The flow domains considered for the simulation consist of casing, impeller, and draft tube. Unstructured tetrahedral mesh was used for all flow domains taking advantage of adjusting mesh density at critical flow zone. The boundary condition at the inlet was specified as known uniform pressure exerted by fluid flow from the penstock. The wall interface was set to no-slip boundary condition over wetted surface. K-epsilon turbulence model was used in this simulation. The simulation results match well with the experimental results for low flow range but perform poorly beyond the best efficiency flow range. The disparities between the simulation and the experiments were from frictional losses in mechanical system and leakage loss which was excluded in the simulation.

Derakhshan and Nourbakhsh (2008) conducted a simulation in pumping and turbine for an industrial centrifugal pump with specific speed of 23.5 using 3D full Navier-Stokes equation and FineTurbo V.7 flow solver [23]. Two different types of mesh grid were used for two flow domains developed by IGG5.5 for the volute and Autogrid5 for the impeller. The simulation model excluded flow domain between impeller hub and casing which excludes leakage loss, disc friction, and mechanical loss. However, these losses were estimated using Thorne and Stephanoff method and then added to the simulation power input. The simulation shows that BEP of the pumping mode gives good match but the turbine operation was not in good coincidence with the experimental data.

3.3. PAT Performance Improvement

Pump has low efficiency in turbine mode and geometric modification of the impeller can lead to an increase in efficiency. Modifications works on PAT were reported through rounding impeller blade and shrouds, installing splitter blades, enlargement of suction eye, and using fixed guide vane. To further understand the internal hydraulic characteristic, Singh and Nestmann (2011) had divided pump control volume into five different flow zones so it can be treated and optimized individually [24]. The control volume domain was enclosed between the inlet and outlet of the pump. By treating the zone as individual section, the alteration can be performed based on local losses. The aim of the experiment is to minimize modification in order to maintain cost-benefit of PAT. Among all geometrical modifications, rounding centrifugal tip is the most beneficial, reducing shock loss at the turbine inlet and increasing efficiency up to 2.4% as shown in Figure 4 [25]. In many cases, average modification work may potentially improve turbine mode efficiency between 2 and 3%. Conversely, the effect must be validated through experimental analysis because there are a large variety and number of pumps operating at various ranges of head and flow.

Figure 4:

Rounding of blade profile and shrouds at impeller inlet [25 –27].

Singh (2005) had conducted an experimental investigation on the effect of impeller rounding for radial flow and mixed flow pump in turbine mode [26]. The modification gives a positive impact on the overall best efficient performance with a raise between 1 and 3%. The reason for the efficiency increase is from the reduction of loss coefficient due to rounding effect.

Suarda et al. (2006) had carried out experimental analysis on the effect of rounding off the impeller tips [27]. The modification was performed by grinding the pump impeller tips to rounded shape, eliminating excessive turbulence at the inlet. A centrifugal pump with specific speed of N_s = 18 and power input of 400 W, head of 13 m, and flow of 2.2 l/s was used in the test. Based on the rotational power generated from the turbine shaft, it was found that the performance after modification had increased at 7.55% compared to the original impeller. Further examination shows that the turbine can rotate at 1500 rpm at high efficiency and therefore can be coupled directly with induction generator without belting.

Derakhshan et al. (2009) had performed a modification by rounding the blades leading edges and shroud [25]. The modification involves rounding up the impeller tips and shrouds by half of the blade thickness eliminating the sharp edges at pump inlet in turbine mode. An industrial pump with a specific speed of N_s = 23.5, flow rate of 120 l/s, and head of 25 m was chosen for the test. The modification gives a 9.4% power increase. However, the authors suggested that the percentage increase of turbine mode could be from reduced inner flow separation or rearrangement of inlet velocity triangle leading to change in the shock loss component.

Sun-Sheng et al. (2012) had studied the effect of splitter blades to a centrifugal pump in turbine mode [28]. A complete microhydro test rig with an electric eddy current dynamometer to regulate and measure the studied pump was constructed to test centrifugal pump with specific speed of 37.5. By introducing splitter blades to the impeller, the fluid flow inside the pump changed. The authors had proposed that by adding splitter blades there is a substantial decrease in pressure fluctuation between impeller blades and pressure gradually decreases along the outlet pipe. The splitter blades reduce the original pressure head and flow rate but increase the turbine mode performance by additional 6.66% from its original condition.

Patel et al. (2013) examine the effect of fixed guide vanes with NACA-4418 profile to part load operating conditions [29]. A smaller impeller size was used to make additional space by replacing 250 mm diameter impeller with 200 mm impeller. The installation of guide vanes at an angle of 75° helps guide the flow tangential with the impeller and thus reduces the loss of kinetic energy. The variation flow velocity inside the casing decreases, which leads to improvement of part load operating condition.

Many researchers have reported that the efficiency of pump in turbine mode can be improved by simple modification such as rounding impeller tips, installation of splitter blades, and reducing impeller size. Other pump modifications such as trimming the impeller diameter can alter the pump characteristic to match the operation condition. In some cases, minor modification to the pump impeller contributes to huge hydraulic improvement leading to increased efficiency.

3.4. Induction Generator

The use of induction motor as generator is usually employed for installed powers below 30 kW. It has been known that an induction motor which is normally coupled directly with PAT can be modified as AC generator and largely used in microhydro applications. Converting induction motor to induction generator is viable by carefully adding capacitor and wiring modification on the motor winding. The application of induction motor as generator is well proven in many microhydro sites [30]. Selection of appropriate capacitance for operating voltage and frequencies can be achieved in many ways. Listed are some of the methods to determine capacitance to initiate self-excitation.

Generally, minimum and maximum capacitance value can be derived from fundamental equations derived from equivalent circuit [31 –33]. Brennen and Abbondanti (1977) had proposed an exciter scheme based on static reactive power generator with fixed capacitor and thyristor control inductors [34]. Harrington and Bassiouny (1998) had proposed using complex impedance matrix analysis loaded with an inductive load which involves algebraic equation solved by iterative approach [35]. The value of capacitor excitation at no load and the desired rate of operation can be determined iteratively.

Different from synchronous generator, induction generator does not have a voltage regulator. The generated frequency and voltage depend mainly on the power factor of the load, rotational speed from the turbine, excitation from the capacitor, and the load current applied to the terminal [30]. Induction Generator Controller (IGC) as power electronic device is used to regulate voltage and frequency output maintaining good power quality [36, 37]. The most popular IGC for microhydro application is Electric Load Controller (ELC). This type of IGC uses solid state electronic controller regulating voltage and frequency, maintaining constant applied load at generator terminal by dummy load. The function of ELC is to eliminate hydraulic control mechanism and let the turbine and generator run at their optimum operating speed.

The philosophy of ELC for rural electrification is to generate stable voltage and frequency using unsophisticated solid state electrical circuit maintaining a constant load at generator terminal. Since the possibility of sensitive electronic equipment is low and common loads are from resistive loads such as fan and lighting [38], the complexity of the control system is kept at a minimum level. This approach can be achieved by generating moderate power quality. With emphasis on optimum solution for remote microhydro, uncontrolled rectifier with a chopper controller dump load is the most favourable induction generator [30, 39]. This control system uses unsophisticated electric circuit with only one dump load and requires no batteries or inverters, which is deemed as simple, cheap, rugged, and reliable, as shown in Figure 5. This system offers satisfactory performance under transient and steady state, for balanced and unbalanced resistive load. An uncontrolled rectifier converts AC voltage to DC voltage and then it is filtered by filtering capacitor producing a variable unity power factor load. An insulated-gate bipolar transistor (IGBT) based chopper operates as load diverter, dumping excessive current to the dummy load maintaining constant applied load at the generator terminal.

Figure 5:

Schematic diagram of three-phase ELC [46 –48].

Induction generators which are coupled with pump were found to be the best electric generators with PAT. With wiring modification and ELC, the system exhibit reliable, simple, and excellent for microhydro application.

3.5. Cost Analysis on PAT

One of the major cost analysis evaluations is to rationalise installation investment of PAT [40]. This will help users to assess the cost-benefit factor of PAT compared to commercial hydro turbine in a range of the operating period. For economic justification, PAT offers low initial cost at low efficiency but commercial hydro turbine has high efficiency at higher cost. The main function of economic benefit analysis is to justify the financial investment benefit to the project. The main economic evaluation aspect is price of unit energy cost ($/kWh) which is a financial indicator for the hydro scheme. In a microhydro scheme, the initial and operation cost vary and are site specific. Typical microhydro system costs include but are not limited to mechanical components, control system, electric distribution system, and civil structures. However, reviewed cost analysis in this study is focussed on electromechanical components supposing that other expenses are identical for any microhydro system. Case studies comparing commercial turbines with PAT have been reported in academic literature but in very small numbers.

Motwani et al. (2013) had carried out a cost analysis for commercial justification of centrifugal pump in turbine mode for hydropower application [41]. The performance characteristic of 3 kW PAT was determined through experimental analysis. It was found that the highest efficiency in turbine mode is around 60%. A conventional hydro turbine, Francis turbine, having an efficiency of 80% was chosen for the economic comparison analysis. The parameters considered in this cost analysis were initial cost of the project, capital recovery factor, annual expenses, discount rate, annual life cycle cost, annual energy generated, and cost of electricity generated per unit. Based on the study, the ratio of Annual Life Cycle cost and the cost of electricity generated per unit between Francis turbine and centrifugal pump in turbine mode were found to be 6.8 and 5.07, respectively. The study had also signified that the cost of electricity generation ($/kWh) for centrifugal pump in turbine mode is 5 times cheaper compared to Francis turbine.

Chuenchooklin (2006) explained the implementation of centrifugal pump in turbine mode to generate power for electrification of Thailand conservation area [42]. A centrifugal pump, model Mono flo MF 65–16 with 3 horse power (hp), was used for the project. PE pipe with inner diameter of 100 mm was used as the system penstock. An electric controller system was installed to regulate the voltage output to 220 V by using parallel system together with series of running capacitors. The cost of the project was approximately USD 4000. It was found that 45% of the expense is for penstock, 37% for electric control, and 18% for PAT and induction generator. The electricity energy production was reported to be 8760 kWh per year and, with energy price of 0.75 cent per kWh, the payback period will be in 6 years.

Arriaga (2010) presented a pico hydro development status in Lao PDR and proposed the use of PAT as a cost-effective solution for electrification for isolated communities [43]. Three power generation options were considered including PAT, commercial Vietnamese crossflow, and PV panels. Cost estimation model divided the expenditure into three categories including energy generation equipment, civil works, and energy distribution system. The analysis shows that a 2 kW PAT system offers a 53% cost reduction for energy generation equipment compared to Vietnamese crossflow turbine. PAT offers the lowest installation cost per kW compared to commercial crossflow turbine and PV panel.

4. Conclusion

This paper reviews previous research works on radial flow and end suction centrifugal pump operating as turbine for standalone microhydro application. Experimental and simulation works show that, by inversing the fluid flow, end suction centrifugal pump can work well in turbine mode. However, BEP for turbine mode is slightly lower than the pump mode. Efficiency improvement is viable by modification of the pump impeller and it was found that rounding impeller tips contribute the highest efficiency improvement. Induction motors which usually come with pump can be modified into induction generator by adding capacitor. ELC can be used to regulate voltage and frequency producing satisfactory power quality by maintaining shaft rotational speed. The use of induction generator further reduces the overall cost and justifies the economic feasibility of PAT as practical options. With low initial cost, energy generation cost is 5 times lower and the payback period is shorter than commercial hydro turbines. Moreover, the know-how maintenance knowledge is readily available in local areas. This further reduces maintenance and operational cost of the system.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

References

Darmawi Sipahutar

Bernas

S. M.

, and Imanuddin

M. S.

, “Renewable energy and hydropower utilization tendency worldwide,” Renewable and Sustainable Energy Reviews, vol. 17, pp. 213–215, 2013.

Leckscheidt

and Tjaroko

T. S.

, “Overview of mini and small hydropower in Europe,” ASEAN Centre for Energy.

Harvey

Brown

Hettiarachi

, and Inversin

, Micro-Hydro Design Manual: A Guide to Small-Scale Water Power Schemes, Practical Action Publishing, Rugby, Warwickshire, 2009.

Vaidya

, “Cost and Revenue Structures for Micro-Hydro Projects in Nepal,” http://www.microhydropower.net/download/mhpcosts.pdf.

Mishra

Singal

S. K.

, and Khatod

D. K.

, “Optimal installation of small hydropower plant—a review,” Renewable and Sustainable Energy Reviews, vol. 15, no. 8, pp. 3862–3869, 2011.

Mishra

Singal

, and Khatod

, “Costing of small hydropower projects,” in Proceedings of the International Conference on Prudent Development and Renewable Energy Resources, pp. 22–25, Chennai, India, 2011.

Hosseini

S. M. H.

Forouzbakhsh

, and Rahimpoor

, “Determination of the optimal installation capacity of small hydro-power plants through the use of technical, economic and reliability indices,” Energy Policy, vol. 33, no. 15, pp. 1948–1956, 2005.

Nautiyal

Varun

, and Kumar

, “Reverse running pumps analytical, experimental and computational study: a review,” Renewable and Sustainable Energy Reviews, vol. 14, no. 7, pp. 2059–2067, 2010.

Williams

A. A.

, “Pumps as turbines for low cost micro hydro power,” Renewable Energy, vol. 9, no. 1–4, pp. 1227–1234, 1996.

10.

Ramos

and Borga

, “Pumps as turbines: an unconventional solution to energy production,” Urban Water, vol. 1, no. 3, pp. 261–263, 1999.

11.

Ranjitkar

Jinxing

, and Tony

, “Application of micro-hydropower technology for remote regions,” in Proceedings of the IEEE EIC Climate Change Technology Conference (EICCCC '06), pp. 1–10, May 2006.

12.

Chappallaz

J. M.

, Manual on Pumps Used as Turbines, 1992.

13.

Barrio

Fernández

Parrondo

, and Blanco

, “Performance prediction of a centrifugal pump working in direct and reverse mode using computational fluid dynamics,” in Presented at the International Conference on Renewable Energies and Power Quality (ICREPQ '10), Spain, 2010.

14.

Páscoa

J. C.

Silva

F. J.

Pinheiro

J. S.

, and Martins

D. J.

, “A new approach for predicting PAT-pumps operating point from direct pumping mode characteristics,” Journal of Scientific and Industrial Research, vol. 71, no. 2, pp. 144–148, 2012.

15.

Burton

J. D.

and Mulugeta

A. G.

, “Running centrifugal pumps as micro-hydro turbines: performance prediction using the area ratio method,” in Renewable Energy, Technology and the Environment, Sayigh

A. A. M.

, Ed., pp. 2839–2847, Pergamon Press, 1992.

16.

Derakhshan

and Nourbakhsh

, “Experimental study of characteristic curves of centrifugal pumps working as turbines in different specific speeds,” Experimental Thermal and Fluid Science, vol. 32, no. 3, pp. 800–807, 2008.

17.

Raman

Hussein

Palanisamy

, and Foo

, “An experimental investigation of pump as turbine for micro hydro application,” in Presented at the 4th International Earth on Energy and Environment, 2013.

18.

Fernández

Blanco

Parrondo

Stickland

M. T.

, and Scanlon

T. J.

, “Performance of a centrifugal pump running in inverse mode,” Proceedings of the Institution of Mechanical Engineers A, vol. 218, no. 4, pp. 265–271, 2004.

19.

Nautiyal

Varun Kumar

, and Yadav

, “Experimental investigation of centrifugal pump working as turbine for small hydropower system,” Energy Science and Technology, vol. 1, no. 1, pp. 79–86, 2011.

20.

Natanasabapathi

S. R.

and Kshirsagar

J. T.

, Pump as Turbine—An Experience With CFX-5.6, 2004.

21.

Yang

S. S.

Derakhshan

, and Kong

F.-Y.

, “Theoretical, numerical and experimental prediction of pump as turbine performance,” Renewable Energy, vol. 48, pp. 507–513, 2012.

22.

Rawal

and Kshirsagar

, “Numerical simulation on a pump operating in a turbine mode,” in Proceedings of the 23rd International Pump Users Symposium, pp. 21–27, 2007.

23.

Derakhshan

and Nourbakhsh

, “Theoretical, numerical and experimental investigation of centrifugal pumps in reverse operation,” Experimental Thermal and Fluid Science, vol. 32, no. 8, pp. 1620–1627, 2008.

24.

Singh

and Nestmann

, “Internal hydraulic analysis of impeller rounding in centrifugal pumps as turbines,” Experimental Thermal and Fluid Science, vol. 35, no. 1, pp. 121–134, 2011.

25.

Derakhshan

Mohammadi

, and Nourbakhsh

, “Efficiency improvement of centrifugal reverse pumps,” Journal of Fluids Engineering, Transactions of the ASME, vol. 131, no. 2, Article ID 021103, 9 pages, 2009.

26.

Singh

, Optimization of internal hydraulics and of system design for pumps as turbines with field implementation and evaluation [Ph.D. thesis], 2005.

27.

Suarda

Suarnadwipa

, and Adnyana

W. B.

, “Experimental work on modification of impeller tips of a centrifugal pump as a turbine,” in Proceedings of the 2nd International Conference on “Sustainable Energy and Environment (SEE '06), pp. 21–23, 2006.

28.

Sun-Sheng

Fan-Yu

Jian-Hui

, and Ling

, “Numerical research on effects of splitter blades to the influence of pump as turbine,” International Journal of Rotating Machinery, vol. 2012, Article ID 123093, 9 pages, 2012.

29.

Patel

V. A.

Jain

S. V.

Motwani

K. H.

, and Patel

R. N.

, “Numerical optimization of guide vanes and reducer in pump running in turbine mode,” Procedia Engineering, vol. 51, pp. 797–802, 2013.

30.

Smith

N. P. A.

, “Induction generators for stand-alone micro-hydro systems,” in Proceedings of the International Conference on Power Electronics, Drives & Energy Systems for Industrial Growth (PEDES '96), pp. 669–673, January 1996.

31.

Chan

T. F.

, “Capacitance requirements of self-excited induction generators,” IEEE Transactions on Energy Conversion, vol. 8, no. 2, pp. 304–311, 1993.

32.

Devabhaktuni

and Kumar

S. V. J.

, “Design of excitation capacitance for self excited induction generator,” International Journal of Computer Science & Communication Network, vol. 1, no. 3, pp. 264–269, 2011.

33.

Sun

Y.-P.

, “Single-phase self-regulated self-excited induction generator with series capacitance,” in Proceedings of the 11th International Conference on Electrical Machines and Systems (ICEMS '08), pp. 102–104, October 2008.

34.

Brennen

M. B.

and Abbondanti

, “Static exciters for induction generators,” IEEE Transactions on Industry Applications, vol. 13, no. 5, pp. 422–428, 1977.

35.

Harrington

R. J.

and Bassiouny

F. M. M.

, “New approach to determine the critical capacitance for self-excited induction generators,” IEEE Transactions on Energy Conversion, vol. 13, no. 3, pp. 244–249, 1998.

36.

Sutanto

Grantham

, and Rahman

, “A regulated self-excited induction generator for use in a remote area power supply,” in Proceedings of the 6th International Conference on Electrical Machines and Drives, Conference Publication no. 37, pp. 234–239, 1993.

37.

Grantham

Rahman

, and Seyoum

, “A self-excited induction generator with voltage regulation for use in a remote area power supply,” in Proceedings of the 3rd International Power Electronics and Motion Control Conference (IPEMC '00) vol. 2, pp. 710–715, 2000.

38.

Foley

, “Rural electrification in the developing world,” Energy Policy, vol. 20, no. 2, pp. 145–152, 1992.

39.

Boldea

, “Control of electric generators: a review,” in Proceedings of the 29th Annual Conference of the IEEE Industrial Electronics Society, pp. 972–980, November 2003.

40.

Bøckman

Fleten

S.-E.

Juliussen

Langhammer

H. J.

, and Revdal

, “Investment timing and optimal capacity choice for small hydropower projects,” European Journal of Operational Research, vol. 190, no. 1, pp. 255–267, 2008.

41.

Motwani

K. H.

Jain

S. V.

, and Patel

R. N.

, “Cost analysis of pump as turbine for pico hydropower plants—a case study,” Procedia Engineering, vol. 51, pp. 721–726, 2013.

42.

Chuenchooklin

, “Development of pico-hydropower plant for farming village in upstream watershed, Thailand,” in Presented at the Agricultural Development Within the Rural-Urban Continuum, 2006.

43.

Arriaga

, “Pump as turbine—a pico-hydro alternative in Lao People's democratic republic,” Renewable Energy, vol. 35, no. 5, pp. 1109–1115, 2010.

44.

Paish

, “Micro-hydropower: status and prospects,” Proceedings of the Institution of Mechanical Engineers A, vol. 216, no. 1, pp. 31–40, 2002.

45.

Parish

Fraenkel

Bolkalders

, and Harvey

A. P.

, Micro-Hydro Power: A Guide for Development Workers, Intermediate Technology Publications, 1991.

46.

Singh

Kasal

G. K.

, and Gairola

, “Power quality improvement in conventional electronic load controller for an isolated power generation,” IEEE Transactions on Energy Conversion, vol. 23, no. 3, pp. 764–773, 2008.

47.

Singh

Murthy

S. S.

, and Gupta

, “Analysis and design of electronic load controller for self-excited induction generators,” IEEE Transactions on Energy Conversion, vol. 21, no. 1, pp. 285–293, 2006.

48.

Singh

Murthy

S. S.

, and Gupta

, “Analysis and implementation of an electronic load controller for a self-excited induction generator,” IEE Proceedings: Generation, Transmission and Distribution, vol. 151, no. 1, pp. 51–60, 2004.

End Suction Centrifugal Pump Operating in Turbine Mode for Microhydro Applications

Abstract

1. Introduction

2. Pump as Turbine (PAT)

3. Research Review

3.1. Experimental Analysis of PAT

3.2. Numerical Analysis on PAT

3.3. PAT Performance Improvement

3.4. Induction Generator

3.5. Cost Analysis on PAT

4. Conclusion

Conflict of Interests

References