Performance Test on Pelton Wheel Turbine

7/18/2019 Performance Test on Pelton Wheel Turbine

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PERFORMANCE TEST ON PELTON WHEEL TURBINE

AIM: To conduct performance test on the given Pelton wheel turbine

APPARATUS: Pelton wheel turbine test rig.

SPECIFICATIONS:

v SUPPLY PUMP / MOTOR

CAPACITY : 5 hp, 3 ph, 440V, 50Hz, AC.

v TURBINE

- Mean Dia. : 250mm

- No. of Buckets : 20

- Dia. Of Jet : 18mm- Runaway Speed : 1800 RPM

- Turbine Head : 24 - 46 mts (min to max.)

v LOADING : Brake Drum

v BRAKE DRUM RADIUS : 0.15m

v MAX. SHAFT OUTPUT

FROM TURBINE : 2.5 hp. (Approx.)

vCOEFFICIENT OF DISCHARGE : Cd = 0.98

DESCRIPTION OF APPARATUS:

The actual experimental facility supplied consists of a Centrifugal Pump

Set, Turbine Unit, Sump Tank, Collecting, Notch Tank arranged in such a way

that the whole unit works on recirculation water system. The Centrifugal Pump

Set supplies the water from the sump tank to the turbine through control valve

which has the marking to meter the known quantity of water. The water after

passing through the Turbine units enters the collecting tank. The water then

flows back to the sump tank through Notch tank which is fixed with 600 V-

notch for the measurement of flow rate.

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The loading of the turbine is achieved by rope brake drum connected to

spring balance. The provision for measurement of turbine speed (digital RPM

indicator), Head on turbine (pressure gauge) are built in on the control panel.

THEORY:

Hydraulic (or Water) Turbines are the machines, which uses the energy of

water (Hydro-Power) and convert it into mechanical energy. Thus the turbines

becomes the prime mover to run the electrical generators to produce the

electricity, Viz, Hydro-electric power.

The turbines are classified as Impulse & Reaction types. In impulse

turbine, the head of water is completely converted into a jet, which impulses the

forces on the turbine. In reaction turbine, it is the pressure of following water,

which rotates the runner of turbine. Of many types of turbine, the Pelton wheel,

most commonly used, falls into the category of turbines. While Francis &

Kaplan falls in category of impulse reaction turbines.

A Turbine acts as a pump in reverse, to subtract energy from a fluid

system. In impulse turbine the fluid energy, first in the potential form, is next

converted wholly into the kinetic energy by means of one nozzle before striking

the runner. The jet ensuing from the nozzle is made to impinge on the runner

tangentially as shown in the figure. A powerful jet issues out of the nozzle,

impinges on the buckets provided on the periphery of the nozzle. In practice

these buckets are usually spoon shaped, with a central ridge splitting the

impinging jet into two halves which are deflected backward. As there is no

pressure variation in flow, the fluid partly fills the buckets and the fluid remains

in contact with the atmosphere. The nozzle is provided with spear mechanism

to control the quantity of the water. The actual energy transfer from jet to wheel

is by changing the momentum of the stream. The impact thus produced causes

the runner to rotate and hence produces mechanical power at the shaft.

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The main parts of a Pelton turbine are:

a) Spear Valve Mechanism :

In a Pelton turbine the flow regulation is done with the help of a spear

shaped needle valve. It consists of a spear connected to a shaft with a

hand wheel at its end.

By rotating the hand wheel the spear valve can be moved inside the

nozzle axially. When the spear is moved forward it reduces the flow area

and hence flow through nozzle reduces, similarly when it is moved

backwards flow increases. Water flow can also be regulated by the gate

valve provided.

b) Runner with Buckets :

The runner consists of a circular disc with a number of evenly spaced

double hemispherical buckets fixed along its periphery. The disc is

mounted on a shaft. The buckets are divided into two parts by a sharp

splitter edge at the centre, which divides striking of the jet into two equal

parts. The buckets are so shaped that after flowing around its inner

surface, the water leaves it with a relative velocity almost opposite in

direction to the original jet but does not interface with the passage of

water to the bucket preceding it during rotation. There is notch cut at

outer rim of each bucket only when it is almost normal to the jet.c) Casing :

The casing of a Pelton turbine has no hydraulic function to perform. It is

provided only to prevent splashing and to lead the water to the tailrace. It

is generally made up of stainless steel and it is fabricated to form ‘D’

section. Front part of the casing is made of acrylic.

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PROCEDURE:

1) Connect the supply water pump-water unit to 3 ph, 440V, 30A, electrical

supply, with neutral and earth connections and ensure the correct

direction of the pump motor unit.

2) Keep the Gate Valve and Sphere valve closed.

3) Keep the Brake Drum loading at zero.

4) Press the green button of the supply pump starter. Now the pump picks-

up the full speed and becomes operational.

5) Slowly open the Sphere Valve so that the turbine rotor picks the speed

and conduct experiment on constant speed and constant head.

6) Note down the speed, load, and pressure gauge readings.

Tabulate the readings.

A. TO OBTAIN CONSTANT SPEED CHARACTERISTICS: (Operating Characteristics)

1) Keep the Spear Valve opening at some speed.

2) For different brake drum loads on the Turbine change the gate valve

setting between maximum and minimum so that the speed is held

constant.

3) Tabulate the readings as per Table given.

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CONSTANT SPEED CHARATERISTICS

METHOD: By keeping sphere valve position maximum and

By changing the Gate valve position.

SPEED OFTHE

TURBINE‘N’ RPM

INLETPRESSURE

‘PI’ inKg/cm2

THROATPRESSURE

‘PT’ inKg/cm2

LOAD ‘F1’

In Kg

LOAD ‘F2’

In Kg

DIFFERENCEOF PI & PT ‘h’

in Kg/cm2

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B. TO OBTAIN CONSTANT HEAD CHARACERISTICS:

1) Keep the Spear valve at a particular position and adjust the gate

Valve setting so as to get corresponding pressure.2) For different Brake Load, note down the speed, pressure gauge,

vacuum gauge. Tabulate the readings as per Table given.

SPEED OF

THE

TURBINE

‘N’ RPM

INLET

PRESSURE

‘PI’ in

Kg/cm2

THROAT

PRESSURE

‘PT’ in

Kg/cm2

LOAD ‘F1’

In Kg

LOAD ‘F2’

In Kg

DIFFERENCE

OF PI & PT ‘h’

in Kg/cm2

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CALCULATIONS

1. Head on Turbine in meters of water ‘H’ :

H = 10 PI in m of water.

Where, P is the Pressure Gauge reading in Kg / cm2.

2. Flow Rate of Water through the Turbine ‘Q’ :

A1x A2 √2g HV

Qtheo

= Cd x ----------------------- m3 /sec

√ (A12

- A22)

Where, A1 = Area of Intel section of venturi = πD12/4 in m

2

A2 = Area of Throat section of venturi= πD22/4 in m2

A1 = Area of inlet section = 1.963 x 10-3

m2

D1 = Inlet diameter = 0.05 m

A2 = Area of inlet section = 4.91 x 10-4

m2

D2 = Throat diameter = 0.025 m

Hv = 10 x h in mtrs

h = (Difference in pressure read from pressure gauge)

3. Hydarulic input to the turbine, Phyd

:

Phyd

= (W Q H)/1000 in kW

Where, W = Specific Weight of the water.

= 9810 N/m3

Q = Discharge in m3/sec (From formulae – 2)

H = Head on turbine in m of water. (From formulae – 1)

4. Break power of the turbine:

2 x π x N x ( F1 - F

2 ) x 9.81 x r

BP = ----------------------------------------

60000

Where,‘N’ is speed in rpm,

‘F1’&‘F

2’ = Load in Kgf,

r = 0.145 m radius of brake drum.

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5. Turbine Efficiency :

% ηtur

= BP / Phyd

x 100

6. Unit quantities - under unit head,

a) Unit speed, Nu = N / H1/2

Where, N = Speed in rpm

H = Head in m.

b) Unit power, Pu = P / H3/2

Where, P = Power output BPshaft in watts

H = Head in m.

c) Unit discharge, Qu = Q / H1/2

Where, Q = Discharge in m

3

/sec H = Head in m.

7. Specific speed,

N P1/2

Ns = ---------

H5/4

Where, N = Speed in rpm

P = Power output BPshaft in watts

H = Head in m.

Part load BPSHAFT

8. Percentage full load = ----------------------- x 100

Max. Load BPSHAFT

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TABLE OF CALCULATIONS(CONSTANT HEAD)

SPEED OF

THETURBINE‘N’ RPM

H in meters Discharge ,Qin m3/sec

Power

Output,BPshaft in KW

Hydraluic

Power, Phyd

in kWTurbine

Efficiency

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UNIT QUANTITIES UNDER UNIT HEAD

Unit Speed,

“Nu”

Unit Power,

“Pu”

Unit Discharge,

“Qu”

Specific speed

“Ns”

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GRAPHS:

FOR CONSTANT HEAD METHOD:

a) UNIT SPEED Vs UNIT DISCHARGE

FOR CONSTANT SPEED METHOD:a) DISCHARGE Vs EFFICIENCY

b) DISCHARGE Vs BP

c) EFFICIENCY Vs % FULL LOAD

RESULTS AND CONCLUSIONS:

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Performance Test on Pelton Wheel Turbine

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