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Question:

Measure the transmission line of a substation. The relation between voltage and current is that the current lags the voltage for 180 degrees, so now I want to ask

  1. Which part of transmission line did I measure, sending end or receiving end?

  2. Is the load an inductive load, a capacitive load or a resistive load?

My answer for 1. and 2. are as below:

  1. I measure it at the receiving end of the transmission line, because I think everyone will want to know about the characteristic of the thing which we receive, not the characteristic of the thing which someone sends. So I think the answer should be "receiving end."

  2. The question says "current lags the voltage for 180 degree", I think it means that \$\theta_i+180=\theta_v\$, that is ,\$\theta_v-\theta_i>0\$, so the load should be an inductive load.

However, the answers are as below:

  1. Receiving end

  2. Resistive load. Why is the load a resistive load, not an inductive load? Can someone tell me the reason?

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1 Answer 1

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You want to see how the load behaves, so measure the current through the load and the voltage between the terminals of the load. You have seemingly decided to do it.

180 degrees phase shift between the voltage and the current of the load needs either pure negative resistance load or pure positive load resistance and inverted polarity for either voltage or current measurement. I guess the latter has happened. Reactive load case should be seen as 90 or -90 degrees phase shift, no matter is one of the polarities inverted or not.

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  • \$\begingroup\$ oh i know which part of my thinking about 2 is wrong,thank you \$\endgroup\$
    – shineele
    May 11, 2020 at 10:13

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