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California State University Northridge

College of Engineering & Computer Science

Power Measurement Experiment

Professor: Arrincon, Javier

February 23, 2018

ME491

Written by: Khaled Aldoughji

Group 3

Abstract:

Dynamometer is the device to measure the speed of the rotating shaft in RPM. The speed in RPM is used to calculate power supplied to rotate the shaft with help of torque on it. The Shaft is supported on the bearing which act as the support acting member on shaft length. The arm length and the load application on the shaft length determines the torque being produced. Power of the shaft is the product of the angular speed and the torque. The brakes in the experimental setup are the hydraulic brakes which helps in applying load on the rotating shaft when load has to be increased brakes are applied. The efficiency of the experiment is the output which is power delivered by input power supplied. Efficiency and power are maximum at speed of 1484.2 RPM.

Introduction:

Power is the product of shaft torque transmitted to the angular speed. The power is the input electrical power supplied to the motor which rotates the shaft. The rotating shaft is supplied by electrical power and the load application is performed by using hydraulic brake which slows down the speed of the shaft. The hydraulic brake dynamometer in this experiment uses the shearing of a fluid caused by the rotation of a rotor mounted to the shaft. The load against the shaft is varied by changing the fluid level in the housing. The hydraulic brake dynamometer is driven by an electric motor. We will use the dynamometer to measure the motor efficiency as a function of load.

Theory:

The equation to calibrate the shaft power was given as:

……………………………………………………………………………….... (1)

Where,

T= Torque

= speed

Whereas, during the analysis the shaft was measured using other power factors and thus was given by:

……………...……………………………………………………………… (2)

Where,

F= reaction force

L= exerted at a moment arm of length

N = rotational speed

C1 = unit conversion factor

The error propagation was using the equation given as:

………………………………………...……….. (3)

The equation for efficiency was given as:

…………………………………………………………….…..…….. (4)

Where,

= unit conversion constant

= electrical input power

Later, Eq. (4) was calibrated and given as:

………………………………………………..……. (5)

Where

and were data points collected for different loads

Procedure:

The weigh tank was initially set at 20 and 40 lb and one by one the weights were applied to the equipment. To pass out streaming of the fluid a three-way valve was mounted between the outlet manifold and the weigh tank.

On passing of fluid, the flow rate was controlled using the control valve. However, to measure the flow rate the control valve was opened for weigh tank, paddlewheel meter, venturi and the rotameter.

Here the time interval required to collect a certain amount of water was determined. To determine rotameter reading the scored line was set with 3/8 below the top of the float, relative to the metal scale.

Further, the pressure difference obtained from venturi gauge was compared with flow rate. The control valve reduced the flow rate by about 1 gpm.

The machine had malfunction due to which experimental data is obtained from instructor.

Results & Discussion:

1) Plot the shaft power in units of horsepower versus motor speed in RPM.

Figure 1: Power vs Speed

The above figure 1, is the shaft power as function of speed. The error bars are the uncertainty in the speed and the power.

The curve for the power increase with the increase in the speed. The maximum efficient shaft operating point is achieved after which the curve drops the power over the increasing speed.

The power of the shaft is dependent on the input electrical power which also controls the speed of the rotating shaft. The load is decreased which causes the shaft to rotate with higher angular speed with help of electrical power supplied.

Figure 2: efficiency vs Speed

The figure 2, has the shaft efficiency plotted as the function of speed. The graph has the efficiency curve which increases with the increase in the speed. The efficient after reaching the maximum point on further increase in the speed has a decrease in the efficiency. The load decrease causes the increase in the efficiency of the rotating shaft.

Table 1: Results and Uncertainty

From the table above the torque given to the shaft, from the motor with electrical input power is used to calculate the power output of the shaft from applied load and speed. The efficiency and power are related with each other, if one increases the other follow. The uncertainty in the efficiency is less than uncertainty in output power of the shaft. The shaft has the efficient with increases with the output power and uncertainty of it follows similar pattern. The reason to increase and decrease if the power, efficiency is when shaft rotating at high speed it will deflect from is axis of rotation which reduces the power and decreases efficiency. The uncertainty accounts for the calculated results and are in agreement with each other. The obtained efficiency and power values are under the experimental resolution and their respective uncertainties.

Conclusion

The experiment helps in measuring the motor efficient with help of dynameters and applied load on the input motor shaft. The electrical input is controlled, by reducing the load on the shaft which increases the torque due to rotation of the shaft increases in speed. The experiment determines the speed, at which the motor can be operated with causing any loss of electrical power and receiving maximum efficiency. Overall experiment was successful.

Appendix

Experiment data

Power vs Speed

Motor Speed in RPM

Shaft power in horse power HP

Efficiency vs Speed

Motor Speed in RPM

efficiency