05-VAWT Generator Testing

Transcription

1 Introduction The purpose of this module is to measure and calculate the generated voltage as a function of the rotational velocity (revolutions per second). This will be accomplished by connect the generator shaft to a drill press chuck, varying the drill speed and using a Digital Voltmeter (DVM) measure the generator voltage and the voltage frequency. A tachometer will be used to measure shaft rotation rate in revolutions per minute (RPM) and related to the voltage frequency. At the end of this module you will know how many volts are generated per shaft revolution. Sinewave Voltage Waveform The generator we will be testing uses four magnets and four coils. Faraday s Law tells us that for a four pole generator, each shaft revolution produces two sinewaves, or 2Hz and a revolution per second (60RPM). Refer to for a more complete discussion of sinusoidal waves. A brief summary of related facts follows: 1 Sine waves per pair of magnetic poles E RMS = 0.707E P E P For a 4 Pole generator ( Frequency in Hz) = (Shaft Revolutions per second)/2 F (Hz) = rps/2 Revolutions per minute (RPM) = Revolutions per second x 60 Root-Mean-Square Voltage (RMS) From the figure you can see that a sinewave is a alternating voltage (AC) that has both positive and negative values. An average of these values is zero. However, a sinusoidal electric current will heat a resistive load just like a battery or DC current will. The value of that voltage is of the peak voltage ( Ep ). This means for a given electrical load (RL) the AC-RMS voltage will produce the same heat (power) a battery of the same value ( 10 v-rms = 10 v-dc). In this module all AV voltages will be measured as RMS voltages. We will not have to know the Ep value. Jbernardini Fall 2016 Page 1

2 Generator Test Procedure 1. Align the turbine shaft in the drill press chuck. (See figure below) Generator Test Setup 2. Carefully tighten the chuck, allowing the shaft to center itself. 3. Connect the DVM to the generator coils. (the ones not connected to anything). 4. Measure the resistance using the ohmmeter. You should the total coil resistance plus the test lead resistance (approximately 14 ohms). If you do not get this troubleshoot the problem (loose wire?) 5. Change the DVM to ac Volts. 6. Turn the power supply voltage knob the extreme counter clockwise position. 7. Turn on the power supply. 8. Adjust the power supply to start turn the shaft. You should start to see waveform appear on the DVM screen. Jbernardini Fall 2016 Page 2

3 9. Continue to increase the voltage until you get close to the target RPM and frequency. 10. Record the actual voltage, RPM and frequency. 11. Repeat the procedure for the target values in the table below. 12. Repeat the steps to obtain the LOAD Test data. 13. Record all data in your journal. Prototype Wind Turbine Drill Press Data -No Load Target Values Measured (Actual) Calculate RPM rev/min F (Hz) 4-Pole Z (rps) rev/sec RPM rev/min F (Hz) 4-Pole V rms -MES (volts) Z (rps) rev/sec V rms -CAL (volts) Load Testing Procedure This involves connection various resistors across the output of the generator (DVM) terminals and measuring the resulting voltage (V L ). Load Resistors 1. Adjust the drill speed to 480 RPM. 2. Using a jumper connector connect a load resistor starting with the highest value. 3. Measure the resulting voltage with the DVM. 4. Repeat the measurements for all load resistor values. 5. The frequency should remain the same for all measurements. Jbernardini Fall 2016 Page 3

4 R g = RPM rev/min F (Hz) 4-Pole Load R L (ohms) Measured Load Volts V L Calculated Load Volts V L The following variables and equation will allow us to predict the open circuit voltage generated by the turbine. Data Analysis Fill in the table below for your analysis Value N-Number of loops of wire A Area of enclosed loop (m2) P Number of poles 4 B Magnet strength (Tesla) Z- revolutions per second ( Variable F Frequency Variable Sample Data Nominal N - Number of loops of wire 888 A - Area enclosed by loop (m 2 ) P - Number of Magnetic poles 4 B - Magnetic pole strength (Tesla) 0.1 Calculated No-Load rms Voltage Z - Rotational velocity of magnets (rps) below V rms = * N *A *P *B *Z F - Frequency of Voltage (Hz) below 1. Using the generator equation produce the Excel spreadsheet as shown below. Place all information in the cells indicated in the example. Jbernardini Fall 2016 Page 4

5 2. From the analysis calculate the generated volts per 100 RPM from both the generator equations and the measured data. 3. This can be calculated for data or the data graph Volts per 100 RPM Generator equations Measurements Jbernardini Fall 2016 Page 5

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