A question regarding transmission line

In summary: If the load impedance is higher than the characteristic impedance, the load already experiences Vmax.This means that the voltage and current are working together and the wave can be reflected. If you place the load at the position of the Vmax however, there will be no energy reflected back and the problem is resolved.
  • #1
yykcw
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0
When wave is reflected back means power is reflected back and not all power is consumed at the load. But I am thinking if I placed the load at the position of Vmax (of the stationary wave formed by the incident and reflected wave). Isn't that all the power will be dissipated at the load, so there should be no wave reflected back? Why is there a contradiction?
 
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  • #2
If the load impedance is higher than the characteristic impedance, the load already experiences Vmax.
 
  • #3
One way of looking at EM wave reflection is that either the voltage is at max and the current is zero (for an open) or the current is at max and the voltage is zero (for a short). The key is to get the voltage and current to work together. We do this by matching impedances.

There are other, more complicated solutions which rely on frequency and geometry, but those are usually reserved for weird applications. (I saw an air gap transmission line used as a lightning protector for a narrow frequency signal once; clever.)

It is poor design practice to use such clever tricks unless they are needed though. One ding and the system might literally burn.
 
  • #4
yykcw said:
When wave is reflected back means power is reflected back and not all power is consumed at the load.
To be more precise, it is energy that is reflected. Power is the rate of flow of energy.

There are two independent signals, one traveling in each direction. The impedance of a transmission line sets the ratio of voltage to current in each of those signals. The sum of those signals generates the standing wave pattern.

In order to get a voltage node there must be an impedance mismatch to reflect the energy in the first place. If you parallel another load somewhere on the line it will change the original line length and so move the voltage node somewhere else.
 

1. What is a transmission line?

A transmission line is a specialized type of electrical circuit that is used to transport electrical energy from one point to another. It is typically made up of conductors, insulators, and other components that help to control the flow of electricity.

2. How does a transmission line work?

A transmission line works by using electromagnetic waves to carry electrical energy from a power source to a destination. The conductors in the transmission line create an electric field and a magnetic field, which interact to create the electromagnetic wave. This wave travels through the transmission line and can be received at the other end.

3. What are the different types of transmission lines?

There are several types of transmission lines, including overhead lines, underground lines, and submarine lines. Overhead lines use tall poles to support the conductors, while underground lines are buried beneath the surface. Submarine lines are laid on the ocean floor to transport electricity between continents.

4. What are the advantages of using transmission lines?

One of the main advantages of using transmission lines is that they can transport electricity over long distances with minimal energy loss. This makes it possible to bring power from remote locations, such as hydroelectric dams, to areas where it is needed. Transmission lines also help to improve the reliability of the electrical grid by providing backup routes for electricity to flow.

5. What are the potential problems with transmission lines?

One of the main problems with transmission lines is that they can cause electromagnetic interference (EMI) with other electronic devices. They can also be vulnerable to weather events, such as lightning strikes or strong winds, which can damage the lines and cause power outages. Additionally, the construction of transmission lines can be controversial because of potential environmental impacts and concerns over property rights.

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