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Understanding 1/3 Period Phase Shift in 50Hz Three-Phase Electrical Systems

Luckey13 15876 6
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  • #1 15397316
    Luckey13
    Level 15  
    Hello, perhaps a trivial question, but what does a phase shift of 1/3 period mean?
    I`m a layman in this topic, but I understand it like this:

    The current has a frequency of 50Hz, if I understand correctly, this refers to voltage changes, and 50Hz means 50 voltage increases and decreases per second, so the period is 0.02 seconds.

    Does this mean that changes in individual phases have the same frequency, but are not synchronized, but shifted in time by 0.02/3 seconds?
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  • #2 15397385
    Rysio4001
    Heating systems specialist
    Hello.
    Buddy Luckey13, you explained it very confusingly, but it looks like you understand it well.

    Below I have drawn a graph with voltage waveforms for three phases L1, L2 and L3. It shows very well what is going on.
    As you can see, the individual phases L1, L2 and L3 are shifted by an angle of 120°. Shifting by an angle of 120° is your 0.02/3s.
    I also marked the period for the L1 phase. The situation is similar for phases L2 and L3.

    Understanding 1/3 Period Phase Shift in 50Hz Three-Phase Electrical Systems
    Regards.
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  • #3 15397544
    Luckey13
    Level 15  
    Convoluted, because I had virtually no knowledge on the subject ;)
    Out of curiosity, I have one more question: if the voltage oscillates at a frequency of 50Hz, what is 230V voltage?
    From what I found, the voltage oscillates from 325 to -325V, the average in such a case would be 0, so where does the 230V come from?
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  • #4 15397725
    Rysio4001
    Heating systems specialist
    Hello.
    Luckey13 wrote:
    ...if the voltage oscillates at a frequency of 50Hz, what is 230V voltage?
    From what I found, the voltage oscillates from 325 to -325V, the average in such a case would be 0, so where does the 230V come from?
    Yes, the voltage oscillates in the range of approximately 325V to -325V, and the voltage of 230V is the effective value of this alternating voltage. The average value is indeed 0, but the average and effective value are not the same. In simple terms, the effective value is as if the lower half-periods of the waveform were transferred (reflected) to the upper part of the graph, and then the average was taken.
    For sinusoidal waveforms, the maximum voltage value is equal to √2 times the effective value. Hence √2*230V≈325V.

    More precisely, the effective value is the value of the direct voltage, the application of which to the resistor will cause a current to flow in it and, as a result, the release of thermal power exactly the same as the application of an alternating voltage of such an effective value to the same resistor.
    Regards.
  • #5 15398361
    phanick
    Level 28  
    Rysio4001 wrote:
    In simple terms, the effective value is as if the lower half-periods of the waveform were transferred (reflected) to the upper part of the graph, and only then the average was taken

    No, this is the average with modulus.
    The effective value is as if you multiplied your sine by itself and then took the average from it. Why? Because the power is P = U * I, I = U/R, so assuming we have some constant load R => P = U^2/R, so the power is proportional to the square of the voltage. Since our voltage is not constant, but alternating, we need some measure to determine it. Why do we take an average? I explained why in a square above
  • #6 15398492
    Luckey13
    Level 15  
    Thank you for helping me understand ;)
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  • #7 15399467
    Anonymous
    Anonymous  

Topic summary

The discussion revolves around the concept of a 1/3 period phase shift in a 50Hz three-phase electrical system. A user seeks clarification on the meaning of this phase shift, which is explained through the relationship between frequency and time. The phases L1, L2, and L3 are confirmed to be shifted by 120 degrees, corresponding to a time shift of 0.02/3 seconds. Additionally, the effective voltage of 230V is discussed, clarifying that it represents the root mean square (RMS) value of the alternating voltage, which oscillates between approximately 325V and -325V. The effective value is essential for calculating power in resistive loads. The conversation also touches on the appearance of a two-phase oscillogram and the nature of 400V voltage waveforms.
Summary generated by the language model.
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