Storage of the electrical energy from wind energy with a capacitor

Transcription

1 Storage of the electrical energy ENT Keywords Wind energy, generator, capacitor, storage, and saturation function Principle Electrical energy can be stored with the aid of capacitors. This experiment shows the effect of the integration of a capacitor into a system comprising a wind turbine and motor. The second part of the experiment is a measurement to determine the effect of different charging times on the runtime of the motor. Equipment *2 Connector, straight, module DB *4 Connector, angled, module DB *2 Connector, T-shaped, module DB *2 Connector, interrupted, module DB *2 Junction, module DB *1 Switch, change-over type, DB *1 Motor with indicating disc, 5 V *1 Blower, 12 V *1 Generator with a 3 mm axis *1 Rotor, 2 pieces *2 Clamp holder with two clamping points *1 Sliding mount for the optical bench *2 Support rod, stainless steel, l = 500 mm *1 Clamp on a holder for the demonstration board 1 Capacitor (Gold Cap), 1 F, DB Additional equipment 1 Demo physics board with a stand Power supply, universal **1 Cobra4 Wireless-Manager **1 Cobra4 Wireless-Link **1 Cobra4 Sensor-Unit Energy **1 Holder for Cobra4, magnetic **1 measure software for Cobra Connecting cable, 250 mm, red Connecting cable, 250 mm, blue Connecting cable, 250 mm, yellow Connecting cable, 500 mm, blue Connecting cable, 750 mm, red Fig. 1: Set-up of the qualitative experiment P PHYWE Systeme GmbH & Co. KG All rights reserved 1

2 ENT Storage of the electrical energy 1 Connecting cable, 750 mm, blue PC, USB port, XP, Vista, Win7 * Included in the ENT 1 set ** Included in the Cobra4 extension set Note Ensure that the blower is operated at 12 V maximum. Be careful when handling the generator. Do not touch the rotating rotor blades. The capacitor must be connected to the voltage source in a manner that ensures that the current is positive during the charging phase and negative during the discharging phase. The Cobra4 Sensor-Unit Energy provides the values for the electric power and work always with a positive sign. 1. Qualitative experiment Set-up - Set the circuit up as shown in Fig. 1, but do not integrate the capacitor at this point. - Ensure the correct polarity of the motor. - Fasten the clamp on the holder tightly to the left edge of the board and clamp in the blower. - Align the blower so that it generates a horizontal air jet along the lower half of the board. - Connect the blower to the DC voltage output of the power supply unit. - The power supply unit is switched off. - Set up a "support bench" for the wind turbine: Place the two clamp holders on the table. Push the slide mount onto the two support rods and guide the rods through the two holes in the clamp holders. - Attach the support bench to the board (Fig. 1) and align it horizontally. - Fasten the 6 blades to the wind generator. - Insert the wind generator into the holes of the slide mount. - The distance between the wind generator and blower should be 5 cm (Fig. 2). - If necessary, correct the distance between the blower and the board and adjust the height of the generator by moving it in the slide mount. Procedure - Switch the power supply unit on and adjust a voltage of 12 V. - After some time, switch the power supply unit off and observe the motor. - Integrate the capacitor as shown in Fig Repeat the experiment and observe the motor. Observation In the first run without a capacitor, the motor stops shortly after the power supply unit has been switched off. In the second run with a capacitor, the rotation of the motor is slightly slower than in the case without a capacitor. When the power supply unit is switched off, the motor runs more slowly but it continues to run for several seconds. The wind turbine also continues to run, but not as long as the motor. Fig. 2: Set-up of the wind turbine and blower 2 PHYWE Systeme GmbH & Co. KG All rights reserved P

3 Storage of the electrical energy ENT Evaluation In the circuit, the capacitor is connected in parallel with the motor. As a result, the current is reduced because of the motor and the motor runs a bit slower than without the capacitor. As long as the wind turbine runs, it generates voltage, thereby charging the capacitor. When the power supply unit (blower) is switched off, the capacitor discharges, thereby resulting in current flowing through the motor of the wind turbine and through the motor in the module. The motors continue to run until the capacitor voltage reaches the minimum voltage of one of the motors. The small motor in the module runs longer, since it only requires very low voltage at the beginning. 2. Quantitative experiment Set-up - Set the circuit up as shown in Fig. 3 and ensure the following: o The polarity of the capacitor. o The change-over switch closes the circuit of the motor. o Ensure that the red plug is connected to the ma socket of the Cobra4 Sensor-Unit Energy. Procedure - Start the PC and Windows. - Connect the Cobra4 Wireless Manager to the USB port of the PC. - Start the "measure" software package on the PC. - Connect the Cobra4 Wireless-Link to the Cobra4 Sensor-Unit. After it has been switched on, the Fig. 3: Experiment set-up with a change-over switch P PHYWE Systeme GmbH & Co. KG All rights reserved 3

4 ENT Storage of the electrical energy Sensor-Unit will be automatically detected and an ID number will be assigned to the Cobra4 Wireless-Link. This number will be displayed. The communication between the Cobra4 Wireless Manager and the Cobra4 Wireless-Link is indicated by way of the data LED. - Switch the Cobra4 Wireless-Link with the connected Cobra4 Sensor-Unit on. The Sensor-Unit and the electrical quantities U, I, P, and W are displayed as the measuring channels. - Load experiment "ENT " (Experiment > Open experiment > ). The program will now open all of the required presettings for the measurement data recording process (Fig. 4). - Switch the power supply unit on and adjust a voltage of 12 V. - Flip the switch (charging the capacitor) and at the same time start the measurement data recording process in "measure". - After 30 seconds, stop the measurement data recording process in "measure" and at the same time switch the power supply unit off. - Repeat the measurement directly afterwards. - The power supply unit remains off. - When starting the measurement data recording process in "measure", flip the switch (discharging the capacitor). - Observe the motor. - Stop the measurement data recording process in "measure" when the motor stops. - Transfer the measurement values to the "measure" main program. - Call up a new measurement with Cobra4. - Repeat the experiment with a capacitor charging time of 60 seconds, and then also with 120 seconds. Fig. 4: Measurement data recording; charging time 30 s 4 PHYWE Systeme GmbH & Co. KG All rights reserved P

5 Storage of the electrical energy ENT Observation When the charging time is longer, the motor also runs longer. The second curve (discharging) is clearly flatter than the first one (charging). Evaluation With the aid of the function "Survey", the following values can be determined: Charging time 30 s 60 s 120 s Runtime 44 s 84 s 110 s Electric work (charging) 2.4 Ws 3.8 Ws 5.3 Ws Electric work (discharging) 0.3 Ws 1.0 Ws 1.6 Ws The longer the capacitor is charged, the more the ratio between the runtime of the motor and the charging time of the capacitor deteriorates. The charging and discharging curves of the capacitor show the typical course of a saturation function (exponential function). When the charging time is extended, e.g. by 30 seconds, the additional energy that is stored is less than the energy that has already been stored during the first 30 seconds. During the discharging phase, the electric work is clearly less than during the charging of the capacitor. This is due to the fact that a capacitor is subject to relatively large losses, e.g. by natural discharging. The motor is also subject to losses in the form of friction. Application Compared to batteries with chemical storage media, capacitors offer the great advantage of being able to supply the stored electrical energy in a direct manner, since the energy does not need to be converted. Especially in the case of higher voltages, capacitors have a time advantage which is why they are often used in high-voltage power plants. Fig. 5: Measurement data evaluation; charging time 120 s P PHYWE Systeme GmbH & Co. KG All rights reserved 5

6 ENT Storage of the electrical energy Notes Corresponding student experiments TESS EN 5.7 Storage of the electrical energy from wind energy with the aid of a capacitor (P ) For the execution of the experiment without a PC, the items on the list (page 1) that are marked with (**) must be replaced with the following items: Experiment P Cobra4 Mobile-Link Cobra4 Sensor-Unit Energy Cobra4 Display-Connect, transmitter and receiver set Holder for hand-held meters Large-scale display Experiment P Work and power meter PHYWE Systeme GmbH & Co. KG All rights reserved P