CE 322
Hydraulics
I.
Pelton Turbine
Objectives
The objectives of this experiment are: to obtain a feel for water horsepower, brake horsepower,
the efficiencies of hydraulic and electric machines, the range of operating speeds for a
turbine/generator, and the concept of an optimum operating point.
II.
Theoretical Background
Fundamentals of Circuits
Ohms law
The voltage across any resistive element is equal to the resistance multiplied by the current.
V=IR
Power
The power dissipated by an element is equal to the voltage across the element multiplied by the
voltage across the element. Using substitution it can also be shown that the voltage squared
divided by the resistance of the element yields power dissipated by that element.
P = VI = V2/R
Fundamentals DC Machines
DC machines, in general, consist of two major components. These components are the rotor and
stator. The stator is stationary and facilitates the magnetic field. The rotor in a DC machine is the
rotating component that drives or is driven by the power on the rotating shaft (prime mover).
The basis behavior of this comes from two key concepts. Firstly, that current flowing through a
magnetic field will generate torque and vice versa (torque -> current). Secondly, the rate at
which a wire rotates within a magnetic field is directly proportional to the voltage generated on
the wire.
T= kφI
V= kφω
The kφ term in the equation above is referred to as the magnetization constant and varies directly
to the strength of the magnetic field across the rotor. This term is generally characterized
experimentally using a combination of blocked and open rotor tests. This has been done for the
machine used in this experiment.
Kφ=.868 V-s
Because a permanent magnet supplies the field kφ is constant.
Page 1 of 4
CE 322
Hydraulics
III.
Pelton Turbine
Equipment Description
This lab is to be performed on a hydraulic assembly and a model pelton impulse turbine. The
bottom portion of the assembly is a sump tank. A centrifugal pump draws water from the sump
and feeds it to the turbine. The spent water is dumped into the sump tank for recirculation.
The turbine sits over the sump tank on the top of the assembly. The flow into the turbine is
controlled by a spear valve assembly. The other function of this assembly is to form a solid water
jet directed at the turbine buckets from left. A pressure gauge mounted on the assembly indicates
the pressure head (in meters) of flow approaching the spear valve.
For this experiment, we will determine the efficiency of the system (the spear valve assembly,
the turbine, and the generator) instead of the turbine runner alone. The jet velocity, although not
directly measurable, can be estimated from the pressure head with some approximating
assumptions.
A load to the turbine is applied by a permanent magnet DC machine mounted on top of the
hydraulic bench with the pelton wheel. This generator consists of a stator and rotor permanent
magnet(s) and armature leads that connect to an electric load. The machine is coupled with to
the pelton wheel through a torque transducer. By raising (or lowering) the resistance of the
electrical load, the torque applied to the running turbine can be decreased (or increased). Facing
the turbine, its rotation is counterclockwise. The DC machine will generate a voltage and current
and the torque transducer will display the torque on the shaft. The voltage and current will be
measured using volt-multi meters connected in parallel with the load elements.
The speed (in rpm) of the turbine can be measured by a digital tachometer. Aim the tachometer
at the reflective patch on the turbine shaft and press the white switch on its right side to obtain
readings. Speeds from 10 to 30,000 rpm can be measured. The rpm uncertainty is: 0.1 rpm from
10 to 1000 rpm, 1 rpm from 1000 to 6000 rpm, and 2 rpm from 6000 to 30,000 rpm. Please keep
this tachometer dry as it is not water proof.
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CE 322
Hydraulics
IV.
Pelton Turbine
Procedure
1. Make sure the spear valve is fully closed. Plug in the power cord. Measure the distance
between turbine shaft center and the center of the buckets and the distance from the pump
shaft to the mounted force gauge.
2. Turn the pump on to slow speed, i.e. switch position 3. (The switch is located on the
control box).
3. Set the resistance to its maximum setting if it is not already.
4. Open the spear valve slowly 3 ½ turns.
5. Measure the turbine speed. (This is the maximum speed at the set spear valve position).
6. Measure the flow rate with the digital flow meter, the rpm of the pump, and the force on
the pump force gauge.
7. Reduce the resistance of the load. Obtain the rpm, the voltage across nodes A - D and A –
B, and torque readings from the digital displays.
8. Repeat step 7 no fewer than 15 times. You want to span the turbine speed from runaway
to nearly zero rpm.
9. Open the valve 1 ½ turns more and repeat experiment.
10. Turn the pump to high speed, switch position 2.
11. Repeat steps 5 to 9.
12. Close all the needle valve. Turn the pump off (with the red button on the control box) and
unplug the power cord.
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CE 322
Hydraulics
Pelton Turbine
Report Outline (Minimum Requirements)
1. Tabulate all raw data and provide a complete set of sample calculations on one data point.
2. Establish water horse power versus buckets speed curve at the two spear valve positions.
3. Establish generator-horse power versus bucket speed curve at the two spear valve
positions.
4. Establish system efficiency versus bucket speed curve at the two spear valve positions.
Show power at each of these locations: Electrical into the pump motor, mechanical into
the pump, hydraulic out of the pump, mechanical out of the turbine, and electrical out of
the generator
5. Discuss the results, including experimental errors and uncertainties.
Report Due Date: One week after data is taken.
Electrical Schematic:
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