Hydroelectric Power Plant Tip Final.97

HYDRO-ELECTRIC POWER PLANT

Hydro-electric Power Plant

• Electric power is produced by falling water that rotates aturbine.

• The potential energy of water at high level is converted tomechanical energy by the turbine and the mechanical energyis converted to electrical energy by the generator.

• The advantage of hydroelectric power plant is that it needsno fuel and the dam can be used as flood control andirrigation.

• Most of the hydroelectric power plant are used to cope uppeak loads because they can be easily started and stopped.

Basic Parts of High-Head Hydroelectric Plant


•Reservoir – stores the water coming from the upper river or water falls.

•Headwater – the water in the reservoir.

• Spillway – a weir in the reservoir which discharges excess water so that the heads of the plant will be maintained.

•Dam – the concrete structure that encloses the reservoir.

• Silt Sluice – a chamber which collects the mud and through which the mud is discharged


• Trash Rack – a screen which prevents the leaves, branches and other water contaminants to enter into the penstock.

• Valve – opens or closes the entrance of water into the penstock.

• Surge Chamber – a standpipe connected to the atmosphere and attached to the penstock so that the water will be at atmospheric pressure.

• Penstock – the channel that leads the water from the reservoir to the turbine.

• Turbine – converts energy of the water into mechanical energy.


• Generator – converts the mechanical energy of the turbine into electrical energy output.

• Draft tube – connects the turbine outlet to the tailwater so that the turbine can be set above the tailwater level.

• Tailrace – a channel which leads the water from the turbine to the tailwater.

• Tailwater – the water that is discharged from the turbine.

Run-of-the-River (Low Head) Hydroelectric Power Plant

• Pondage – the water behind the dam of a run-of-the-river hydroelectric power plant.

Pumped Storage Hydroelectric Power Plant

• Pumped storage plant –is a hydroelectric plantwhich involves the use ofoff-peak energy to storewater and to use the storedwater to generate extraenergy to cope with thepeak load. Pumped storagehydroelectric plant is alsotermed as HydraulicAccumulator.

Classification of Hydraulic Turbines

1. Impulse (Pelton) Turbine – high head and low flow


2. Reaction Turbine

a. Francis Turbine – low head and high efficiency


b. Propeller (Kaplan) Turbine – very low head and efficiency is lower that Francis.

Selection of Turbine Type based on head

Net Head

Up to 70 ft

70 ft to 110 ft

110 ft to 800 ft

800 ft to 1300 ft

1300 ft and above

Type of Turbine

Propeller Type

Propeller type or Francis

Francis Type

Francis or Impulse

Impulse

Performance of Hydroelectric Power Plant


Continuation…Friction Head LossWhere:

f = coefficient of friction

L = total length of pipe, in meters

V = velocity, m/sec

g = 9.81 m/sec2

D = inside diameter, meters

(Friction head loss is usually expressed as a percentage of the gross head.)













HYDROELECTRIC POWER PLANT

PROBLEMS

Problem 1

A hydroelectric power plant having 50 sq. km reservoir area and 100m head is used to generate power. The energy utilized by theconsumers whose load is connected to the power plant during a five-hour period is 13.5x106 kW-hr. The overall generation efficiency is75%. Find the fall in the height of water in the reservoir after 5-hourperiod.

a. 2.13 m c. 3.21 m

b. 1.32 m d. 0.53 m

Problem 2

45 kW of the shaft power is developed by a turbine working underan available head of 40 meters. Assuming hydraulic and mechanicalefficiencies to be 87% and 95% respectively, what is the dischargethrough the turbine in m3/s?

a. 0.0345 c. 1.511

b. 0.139 d. 1.234

Problem 3

A vertical draft tube is installed on a Francis turbine with a head of38 meters at the inlet while discharge is 2.1 m3/s. The hydraulicefficiency is 0.87 and overall efficiency is 0.84. The velocities at theinlet and exit of the draft tube are 5 m/s and 1.5 m/s, respectively.The top of the draft is 1 m below the center line of the spiral casingwhile the tailrace (water) level is 3 m from the top of the draft tube.There is no velocity of whirl at either top or bottom of the draft tubeand leakage losses are negligible. What is the power output of theturbine in kW?

a. 746.9 c. 901.3

b. 632.9 d. 832.6

Problem 4

A Pelton Wheel is to be designed to run at 300 rpm under aneffective head of 150 m. The ratio of the nozzle diameter to thediameter of the pitch circle is 1/12. assuming efficiency of 84%, whatis the size of the wheel in meters. Assume speed ratio of 0.45.

a. 1.05 c. 1.55

b. 2.00 d. 2.86

Problem 5

A hydro-electric generating station is supplied from a reservoir ofcapacity 6,000,000 m3 at a head of 170 m. Assume hydraulicefficiency of 80% and electrical efficiency of 90%. The fall in thereservoir level after a load of 15 MW has been supplied for 3 hours,if the area of the reservoir is 2.5 sq. km is closest to:

a. 5.39 cm c. 5.98 cm

b. 4.32 cm d. 4.83 cm

Problem 6

A hydroelectric plant discharges water at the rate of 0.75 cubic meterper second and enters the turbine at 0.35 mps with a pressure of275kPa. Runner inside diameter is 550 mm, speed is 520 rpm andthe turbine efficiency is 88%. Find the turbine speed factor.

a. 0.638 c. 0.368

b. 0.386 d. 0.836

Problem 7

The nozzle efficiency of a Pelton turbine is 90%. Find the velocity ofwater at the nozzle exit if the head is 180 meters.

a. 53.48 m/s c. 77.4 m/s

b. 65.4 m/s d. 89.4 m/s

Problem 8

A hydro-electric plant in Loboc, Bohol discharges 205 ft3/sec andreduces the pressure from 50 psi to 30 psi. Determine the poweroutput in MW.

a. 0.80 MW c. 1.80 MW

b. 1.20 MW d. 2.40 MW

Problem 9

A hydraulic turbine receives water from a reservoir at an elevation of100 meters above it. What is the minimum water flow in kg persecond to produce a steady turbine output of 50 MW?

a. 50,247 c. 50,672

b. 50,968 d. 50,465

Problem 10

The pressure drop across a turbine is 25 psi. The flow rate is 55gallons per minute. Calculate the power output of the turbine.

a. 0.802 hp c. 1.05 hp

b. 0.41 hp d. 2.54 hp

Problem 11

A reaction turbine develops 500 bhp. Flow through the turbine is 50cfs. Water enters at 20 fps with a 100 ft pressure head. The elevationof the turbine above the tailwater level is 10 ft. Find the effectivehead.

a. 130 ft c. 110 ft

b. 120 ft d. 116.2 ft

Problem 12

The hydraulic efficiency of hydro-electric turbine is 85%, find thedischarge in liters per second. Power developed is 10,500 kW andoperating under a head of 320 m.

a. 3,935 L/s c. 9,533 L/s

b. 3,395 L/s d. 5,933 L/s

Problem 13

A horizontal tube supplies 280 liters per second of water to ahydraulic turbine. The net head is 46.50 m. Determine the powersupplied to the turbine.

a. 117.7 kW c. 137.7 kW

b. 127.7 kW d. 157.7 kW

Problem 14

What is the overall efficiency of the turbine if the power developed is15,000 kW at a head of 170 meters and the nozzle discharge is 10cubic meters per second?

a. 70.09 % c. 79.98 %

b. 89.94 % d. 90.96 %

Problem 15

If the available water power of a hydro-station is 3,500 MW and thehead of water is 280 meters, determine the water rate of flow.

a. 1,420 m3/sec c. 875 m3/sec

b. 12,500 m3/sec d. 1,274 m3/sec

Problem 16

What is the overall efficiency of the turbine if the power developed is12 MW at a head of 150 meters and the nozzle discharge 10 cubicmeters each second.

a. 70.65% c. 81.55%

b. 78.99% d. 89.23%

Problem 17

A reaction turbine develops 500 bhp. Flow through the turbine is 50cfs. Water enters at 20 fps with a 100 ft pressure head. The elevationof the turbine above the tailwater level is 10 ft. What is the turbineefficiency?

a. 65.8% c. 85.8%

b. 75.8% d. 90.5%

Problem 18

A river 60 m wide and 2 m deep flows at 2 m/s. If a hydro-plantdevelops a pressure of 300 kPa gage just before the turbine, whatpower in MW can be developed?

a. 40 c. 56

b. 48 d. 72

Problem 19

The difference between the head race and the tail race of a hydro-electric plant is 220 m. The friction loss through the penstock isequivalent to 10 m. Water flows at the rate of 3.0 m3/sec. Power lossdue to friction in the turbine is 50 kW and the leakage loss is 0.103m3/sec. Determine the electrical power generated in kW if thegenerator efficiency is 90%.

a. 3966 c. 4931

b. 4255 d. 5326

Problem 20

A hydro-electric power plant has the following data: catchment area,100 sq. km; average annual rainfall, 150 cm; run off, 90%; availablehead, 400 m; overall station efficiency, 80%. Calculate the power thatit can develop in kw.

a. 11,789 c. 12,435

b. 10,567 d. 13,435

Problem 21

In a certain municipality, a proposed hydro-electric plant site has thefollowing data: the elevation of the head water is 500 m, tail waterelevation is 390m, average annual water flow is determined to beequal to that volume flowing through a regular channel 5m wide and1.0m deep and average velocity of 6.0 m/sec. Assuming that theplant will operate 345 days a year. Find the annual energy in kW-hrthat the power site can develop if the hydraulic turbine that will beused has an efficiency of 83% and generator efficiency of 93%.Assume a head loss of 5% of the available head.

a. 176,561,261 kW-hr c. 146,561,261 kW-hr

b. 196,561,261 kW-hr d. 116,561,261 kW-hr

Problem 22

The water surface on the dam of a certain hydroelectric power plantin Mindanao is at an elevation of 165 m, while the water surface justat an outlet of the gate is 160 m. The head gate has an opening of1.25m x 1.25m leading to the penstock which is fully opened.Assume 70% as coefficient of discharge. Determine (1) the quantityof water that enters the hydraulic turbine per second; and (2) the kWoutput of the turbine, assuming 81.5% efficiency and the turbine is110m below the entrance of the penstock.

a. (1) 6.56 m3; (2) 7890 c. (1) 10.8 m3; (2) 9,960

b. (1) 7.45 m3; (2) 8200 d. (1) 15.6 m3; (2) 12,200

Problem 23

A certain community in the mountains of Mindanao plans to put up asmall hydro-electric plant to service 5 closely located barangays estimatedto consume 61,320,000 kw-hr per annum. Expected flow of water is 1,700m3/min. The most favourable location for plant fixes the tail water level at400 m, the manufacturer of the turbine generator set have indicated thefollowing performance data: Turbine efficiency is 85%, generatorefficiency is 91%, losses in head work will not exceed 5% of the availablehead. Determine (1) the head water elevation (HWE); and (2) thesynchronous speed of generator if the number of poles is 4, and thefrequency is 60 Hz.

a. (1) 434 m; (2) 1800rpm c. (1) 344 m; (2) 1200 rpm

b. (1) 388 m; (2) 1500 rpm d. (1) 299 m; (2) 1000 rpm

Problem 24 (situational)

A proposed hydroelectric power plant in Bohol has the following data:

Elevation of normal head water…………………………… 200 m

Elevation of normal tail water……………………………... 80 m

Loss of head due to friction…………………………………. 10 m

Turbine discharge at full gate opening…………………. 6.5 m3/sec

Turbine efficiency at rated capacity…………………..... 85 %

Turbine is directly connected to 60 cycle AC generator.


A. Determine the effective head of the hydro-electric power plant.

a. 80 m c. 110 m

b. 99m d. 160 m

B. Find the brake power of the turbine in kW.

a. 4162 kw c. 5562 kw

b. 4962 kw d. 5962 kw


C. Find the number of poles of the generator if the rotative speed is

900 rpm.

a. 2 poles c. 8 poles

b. 4 poles d. 10 poles

D. Find the kW output of the direct connected generator if the efficiency is 92%

a. 5485 kW c. 5584 kW

b. 4585 kW d. 4855 kW


A certain hydro storage plant in Laguna has 18,000 kW ratedcapacity, with a utilization factor of 70%. For a 2.0 hr peak,determine the hydraulic impoundment of water required, withfrictional loss of 4 ft. Dam elevation at 130 ft and hydroelectricturbine elevation of 40 ft and a tail race at elevation 30 ft. Generatorefficiency is 90% and a turbine efficiency of 80% and evaporationfactor of 25%. Assume that the water is pumped from the lowreservoir with friction factor of 10%, pump efficiency of 75% andmotor efficiency of 84%.

a. 51.3 m3/sec c. 71.3 m3/sec

b. 61.3 m3/sec d. 81.3 m3/sec


A. How many kW-hr is required to pump the water needed to carry the peak?

a. 64,911.80 c. 84,911.80

b. 74,911.80 d. 94,911.80

B. What is the overall efficiency of the hydroelectric power plant?

a. 15% c. 30%

b. 20% d. 38%

Problem 26

If it is desired to use a type of hydraulic turbine whose specific speed is 50 rpm to deliver 150 hp at 150 ft head, what will be the corrected speed of the unit?

a. 1143 rpm c. 1943 rpm

b. 1743 rpm d. 2143 rpm

Problem 27

A hydroelectric power station is to be constructed has an averageannual rainfall of 1.5 m. The catchment area is 230 km2 with anavailable head of 40 m. Only 80% of the rainfall can be collected and¾ of the impoundment water is available for power. The load factorof the station is 82%. The penstock efficiency is 95%, turbineefficiency is 80%, and generator efficiency is 90%. (1) Calculate theaverage power that could be generated; and (2) the installedcapacity of the power station.

a. (1) 2,962 kw; (2) 1,549 kw c. (1) 1,962 kw; (2) 1,949 kw

b. (1) 2,762 kw; (2) 2,549 kw d. (1) 1762 kw; (2) 2,149 kw


An existing hydroelectric power plant has the following data and design:

Gross head …………………………………………….. 49.5 ft

Mean flow ……………………………………………… 75 ft3/sec

Length of penstock ………………………………... 80 ft

Penstock diameter …………………………………. 3.5 ft

Assumptions:

Coefficient of friction …………………………….. 0.020

Turbine efficiency ………………………………….. 88%

Generator efficiency ……………………………… 92%


A. Find the net head in ft used by the turbine.

a. 42 c. 49

b. 44 d. 59

B. Find the Hp developed by the turbine.

a. 312 c. 367

b. 339 d. 667


C. Find the standard capacity of synchronous generator.

a. 338 hp c. 388 hp

b. 358 hp d. 489 hp

D. Find the motor rpm assuming 6 poles.

a. 900 rpm c. 1800 rpm

b. 1200 rpm d. 2200 rpm

Problem 29

A mini-hydropower plant has an available head of 5m. The waterflow is 1.25 m3/sec, efficiency of the turbine is 90%, efficiency of thegenerator is 92%. Determine the maximum output of the generatorin kW.

a. 29.5 c. 50.7

b. 42.5 d. 69.5

Problem 30

It is desired to develop a 5MW impulse turbine under an effectivehead of 320 m. The turbine efficiency is 85%. Velocity coefficient ofthe nozzle is 99%. What should be the wheel diameter assuming it is12 times the diameter of the jet?

a. 1.5 m c. 2.1 m

b. 1.8 m d. 2.8 m

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Hydroelectric Power Plant Tip Final.97