Why Standing Wave is discuss only in RF Transmission Lines?

[umery2k75]

For maximum power transformer, source must be match to the load. If this don't happen. We get forward and reflected power.The wave moving toward the load(forward wave) and one moving away the load(reflected wave) will interfere with one another and produce the standing wave.Why discuss with higher frequency transmitter.Maybe for lower frequency 50/60Hz, this effect is reduce to be notice and maybe people don't talk about it.



Why this doesn't happen at low frequency like 50/60Hz. The power that we are using in our daily life at home,offices,etc. For power industry, three phase distribution people never take into consideration the standing wave in AC power circuits.I'm little confused. When I talk about power transmission, load must match the source or maximum power transfer doesn't take place, to minimize the load reflection.When I talk about RF transmission line, load must match or maximum power transfer doesn't take place, because standing waves will create because of forward,reflected waves. Power Transmission/RF tranmission seems to look very similar to each other. So can I apply the concept of standing waves at low frequency for Power transmission.

 

[FvM]

Re: Why Standing Wave is discuss only in RF Transmission Lin

If you are an electrical engineer, you should have heard about this topic in electrical power engineering.

In a short:
- power distribution systems are not generally based on impedance matching. For overland lines, there is however a "natural power" property, that indicates impedance matching.
- standing waves actually matters in power distribution systems, but only up from a several hundred kilometers scale (you may want to think about wavelengths)

In the usual engineering scope, transmission line properties appear as part of reactive net impedance.

By the way, your question would be good for an interview or a PhD examination to check general engineering knowledge.

 

[monnoliv]

Re: Why Standing Wave is discuss only in RF Transmission Lin

Why this doesn't happen at low frequency like 50/60Hz.

It happens of course (same physics everywhere) but as the wavelength is 6000[km], you see nothing. Only engineering long distribution power line takes this into account (for example, detecting the position of a defect along the line can be made by the examination of the time taken by a signal to do the go-back).

 

[flatulent]

Re: Why Standing Wave is discuss only in RF Transmission Lin

This effect occurred in the past on telephone lines that were long. It caused the output voltage to be higher than the input.

 

[umery2k75]

Re: Why Standing Wave is discuss only in RF Transmission Lin

@monnoliv

Did you figure out the wavelength of 50hz by this relation ?
wavelength=300/Freq in Mhz
wavelength=300/(50/1000000))=6000000=6000KM

Added after 12 minutes:

Here are two pictures, one say TIME PERIOD other say WAVELENGTH.

For time period=1/f=1/50Hz=20mS. The time period and wavelength appears similar to each other.I think they both have same meaning and are same.
The constant 300 appears to me to be as the speed of light(miles/hr) in your above equation. I think you are considering the wave 50Hz AC to be travelling at the speed of light and hence Electromagnetic in nature, but as the electrons has a definite speed and are very slow. Did you consider the electromagnetic wave that originates perpendicular and 90' apart from the AC wave?

**broken link removed**

 

[FvM]

Re: Why Standing Wave is discuss only in RF Transmission Lin

In my opinion, you're starting to confuse an originally clear question. The travelling speed of electrical waves along a an
overland line actually equals speed of light, because µr and er are close to 1. It's a bit slower in transmission lines involving other
dielectrica than air, but still in the same order of magnitude.

Travelling speed of waves has nothing to do with speed of electrons in a conductor. Electromagnetic waves in a transmission
lines are different from free electromagnetic waves in several details, but they a ruled by the same basic equations.

 

[monnoliv]

Re: Why Standing Wave is discuss only in RF Transmission Lin

Yes, the wavelength of a 50Hz voltage travelling conductors is about 300000000/50 = 6000 km. It has the same properties as others signals (rf, digital,...).
I think that you're confused with two things.
On the first hand is the propagation of the electromagnetic wave associated with the 50Hz voltage (or any DC voltage), think about a switch that light a bulb (it's instantaneous since the velocity of the current wave is always in the range of the speed of light, it's a real wave along conductors between the switch and the bulb and is not related with the charge displacement).
On the second hand, the displacement of the charges (electrons), these ones have very low speed (depending also strongly of the medium) and, of course, in AC current their mean velocity = 0 (since they always go-back).

 

[umery2k75]

Re: Why Standing Wave is discuss only in RF Transmission Lin

Can I say TIME PERIOD=WAVELENGTH? I'm looking at the above two pictures.

 

[monnoliv]

Re: Why Standing Wave is discuss only in RF Transmission Lin

After a period of 20mS your wave has travelled 6000km
Time period unit: second
Wavelength unit: meter