===== Three-phase AC =====

==== Background information ====
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In a DC network or an AC network with only two live conductors, only a single voltage is available at the end of the line. In contrast, in a three-phase AC network (three-phase current) with the external conductors L1, L2, L3 and the neutral conductor N, the possibility arises to connect to two different voltage levels. The three external conductors can be used individually or together with the neutral conductor to supply electrical loads. This enables the economic supply of consumers with greatly differing power consumption on the same network.
The generator circuit diagram is shown in <imgref Fig-14_V3-generator-circuit>.

{{drawio>Fig-14_V3-generator-circuit.svg}}\\
<WRAP centeralign> <imgcaption Fig-14_V3-generator-circuit | Generator circuit diagram> </imgcaption> </WRAP> 
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At the control panel of your laboratory workstation there are sockets. The designations of the sockets are: L1, L2, L3 and N. Connect these sockets to your breadboard.
**Warning: There is a risk of short circuit!**

==== Experimental Tasks ====

  - Sketch the voltages $U_{\rm 1}$, $U_{\rm 2}$ and $U_{\rm 3}$ using the oscilloscope. 
  - Enter all three line-to-neutral voltages into a single screen image and use a different color for each external conductor. 
  - Also label the waveforms with the corresponding voltages. To do this, measure $U_{\rm 1}$ and $U_{\rm 2}$ as well as $U_{\rm 1}$ and $U_{\rm 3}$ simultaneously. 
  - State the oscilloscope settings you used. \\ \\ <wrap left> {{drawio>Fig-00_V4-Screen-image>.svg}}\\ <imgcaption Fig-15_V4-Screen-image> | Screen image for uF and uC> </imgcaption> </wrap> L1:  $ \frac{V}{\rm DIV} =  $ \\ \\ L2:  $ \frac{V}{\rm DIV} =  $ \\ \\ L3:  $ \frac{V}{\rm DIV} =  $ \\ \\ Time basis: $ \frac{T}{\rm DIV} =  $ \\ \\ \\ \\ \\ 
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  - Draw the phasor diagram of the voltages $U_{\rm L1-N}$, $U_{\rm L2-N}$ and $U_{\rm L3-N}$. 
  - Complete your phasor diagram with the line-to-line voltages $U_{\rm L1-L2}$, $U_{\rm L2-L3}$ and $U_{\rm L3-L1}$. 
  - How large are these voltages?
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{{drawio>Fig-16_V3-Phasor-diagram-three-phase network>.svg}}\\
<WRAP centeralign> <imgcaption Fig-16_V3-Phasor-diagram-three-phase network> | Phasor diagram of the three-phase-network> </imgcaption> </WRAP> 
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===== The Three-Phase Midpoint Circuit =====

==== Background information ====
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The circuit shown in <imgref Fig-17_V3-three-phase-midpoint-circuit> is a three-phase midpoint circuit. 

==== Experimental Tasks ====

  - Build this three-phase rectifier circuit. \\ {{drawio>Fig-17_V3-three-phase-midpoint-circuit>.svg}}\\ <WRAP centeralign> <imgcaption Fig-17_V3-three-phase-midpoint-circuit> | Three-phase midpoint circuit> </imgcaption> </WRAP> \\
  - Enter into the three-phase midpoint circuit, s. <imgref Fig-17_V3-three-phase-midpoint-circuit>, the rectified voltage and the current. Now connect the oscilloscope to the built circuit so that the output voltage at the rectifier can be displayed together with $U_{\rm 1}$ or $U_{\rm 2}$ or $U_{\rm 3}$. Label the waveforms with the corresponding voltages. \\
  - Draw the oscilloscope screen image in another color into the diagram <Fig-15_V4-Screen-image>. \\
  - Which maximum and minimum values of the rectified voltage occur? \\ \\ ${\rm ................................................................................................}$ \\ \\
  - What is the average value of the rectified voltage? \\ \\ ${\rm ................................................................................................}$ \\ \\
  - How large is the ripple frequency? \\ \\
${\rm ................................................................................................}$ \\ \\

===== The Three-Phase Bridge Rectifier Circuit =====
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Build the three-phase bridge rectifier circuit shown in <imgref Fig-18_V3-three-phase-bridge-rectifier-circuit> 
  - Enter the rectified voltage and the current into <imgref Fig-18_V3-three-phase-bridge-rectifier-circuit>. \\ \\{{drawio>Fig-18_V3-three-phase-bridge-rectifier-circuit>.svg}}\\ <WRAP centeralign> <imgcaption Fig-18_V3-three-phase-bridge-rectifier-circuit> | Three-phase bridge rectifier circuit> </imgcaption> </WRAP> \\
  - Connect the oscilloscope so that the voltage after the three-phase bridge can be measured. 
  - Sketch the oscilloscope screen image, s. <imgref Fig-19_V3-Screen-image-three-phase-bridge-rectifier-circuit> 
  - Label the waveforms with the corresponding voltages. 
  - Give the oscilloscope settings used. \\ \\ <wrap left> {{drawio>Fig-00_V4-Screen-image>.svg}}\\ <imgcaption Fig-18_V4-Screen-image> | Screen image for uF and uC> </imgcaption> </wrap> Channel 1:  $ \frac{V}{\rm DIV} =  $ \\ \\ Time basis: $ \frac{T}{\rm DIV} =  $ \\ \\ 
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  - Which maximum and minimum values of the rectified voltage occur? \\ \\ ${\rm ................................................................................................}$ \\ \\ \\
  - What is the average value of the rectified voltage? \\ \\ ${\rm ................................................................................................}$ \\ \\ \\
  - How large is the ripple frequency? \\ \\ ${\rm ................................................................................................}$ \\ \\ \\
  - Now connect a capacitor (electrolytic capacitor) with 100 µF in parallel to the load resistor and sketch the oscilloscope screen image, s. <imgref Fig-20_V3-Screen-image-Rectified-voltage-three-phase-bridge-100-µF>. 
  - Label the waveforms with the corresponding voltages. 
  - Give the oscilloscope settings used: \\ \\ \\ ${\rm ................................................................................................}$ \\ \\ \\ **Warning: When using an electrolytic capacitor (Elko) the correct polarity must be observed!** \\ \\ <wrap left> {{drawio>Fig-00_V4-Screen-image>.svg}}\\ <imgcaption Fig-19_V4-Screen-image> | Screen image for uF and uC> </imgcaption> </wrap> Channel 1:  $ \frac{V}{\rm DIV} =  $ \\ \\ Time basis: $ \frac{T}{\rm DIV} =  $ \\ \\ 
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  - Which maximum and minimum values of the rectified voltage occur? \\ \\ ${\rm ................................................................................................}$ \\ \\ 
  - What is the average value of the rectified voltage? \\ \\ ${\rm ................................................................................................}$ \\ \\
  - How large is the ripple frequency? \\ \\ ${\rm ................................................................................................}$ \\ \\ 
  - Compare all measured circuits and explain the advantages and disadvantages of each circuit. 
  - Name one application for each circuit. \\ \\
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==== Test questions - Three-phase AC ====