I What is the cause of electrical disturbances?

[rudransh verma]

The electromagnetic field can carry waves, some of them are light, others are used in radio broadcast. These oscillatory waves are distinguished by their frequency. The usual pickup that we get from electric currents in the circuits in the walls of the building has a frequency of about 100 cycles/sec. It behaves as field and are called electrical disturbances.
What is a pickup? I don’t fully understand this statement in bold.

If I am correct this is the same current which is usually at 50-60hz but now due to some disturbance(lightening, fluctuations )it’s frequency has increased to 100 hz. Now it behaves as field. This is the same thing that happens on electric poles. Due to power surges a strong dangerous field is setup around it.
Correct me if I am wrong !

 

[.Scott]

In this case I believe "the usual pickup that we get" is intended to be taken literally - as in what is happening to a human body in an electric field. In this sense, "pickup" is similar to the what happens with the pickup in an electrical guitar.

The reference to 100Hz is likely intended to cover all frequencies in that general band - including 50Hz, 60Hz, and the second harmonics 100Hz and 120Hz.

The frequency of the power supplied by electric utilities is very regulated. Anything that changes the 50Hz or 60Hz power by more than 0.5Hz is likely to kill the power completely.

Electrical disturbances are simply unwanted electric currents or electric fields. They would include the 50-60Hz fields produced by household power currents.

 

[rudransh verma]

In this case I believe "the usual pickup that we get" is intended to be taken literally - as in what is happening to a human body in an electric field. In this sense, "pickup" is similar to the what happens with the pickup in an electrical guitar.

The reference to 100Hz is likely intended to cover all frequencies in that general band - including 50Hz, 60Hz, and the second harmonics 100Hz and 120Hz.

The frequency of the power supplied by electric utilities is very regulated. Anything that changes the 50Hz or 60Hz power by more than 0.5Hz is likely to kill the power completely.

Electrical disturbances are simply unwanted electric currents or electric fields. They would include the 50-60Hz fields produced by household power currents.

You mean pickup is the shock we receive on touching a bare wire!

 

[.Scott]

You mean pickup is the shock we receive on touching a bare wire!

No. It is what you see on an oscilloscope when you make a good electrical connection between your finger and the scope probe. Your body acts like as an antenna.

 

[rudransh verma]

No. It is what you see on an oscilloscope when you make a good electrical connection between your finger and the scope probe. Your body acts like as an antenna.

So in a oscilloscope we can see the frequency of the pickup that we get from electric signal passing through it. This pickup is a graphical representation of current.

 

[.Scott]

You have the basic idea - but you need to discriminate between current (amps) and potential (volts).

Current is the actual flow of electrons. Voltage is the force behind that flow that allows the flow to occur even when there is resistance. So voltage is like the water pressure behind your faucet.

The oscilloscope normally measures potential (ie, voltage), not current.
The reason that the oscilloscope is able to show the signals that you pick up is that the probes are very high impedance (commonly 100Mohms). This actually minimizes the current. Otherwise the probe would tend to short out your signal.

 

[rudransh verma]

You have the basic idea - but you need to discriminate between current (amps) and potential (volts).

Current is the actual flow of electrons. Voltage is the force behind that flow that allows the flow to occur even when there is resistance. So voltage is like the water pressure behind your faucet.

The oscilloscope normally measures potential (ie, voltage), not current.
The reason that the oscilloscope is able to show the signals that you pick up is that the probes are very high impedance (commonly 100Mohms). This actually minimizes the current. Otherwise the probe would tend to short out your signal.

But the frequency of current in houses is 50-60hz not 100hz. If I’ll connect the device to a household circuit I will get 50-60 hz not 100hz. Don’t we?

 

[.Scott]

You will get either 50 or 60Hz.
It says "about 100 cycles per second". Given a spectrum that runs from below vertical sync rates (30 Hz) to beyond gamma rays, 50 Hz is "about" 100 Hz.

 

[rudransh verma]

You will get either 50 or 60Hz.
It says "about 100 cycles per second". Given a spectrum that runs from below vertical sync rates (30 Hz) to beyond gamma rays, 50 Hz is "about" 100 Hz.

Sorry! I don’t get it. Can you elaborate?

 

[berkeman]

Sorry! I don’t get it. Can you elaborate?

He is just saying that both 50Hz and 60Hz are "about 100Hz". It seems the author was just speaking in generalities. Can you provide a link to where you got that quote? Thanks.

 

[rudransh verma]

He is just saying that both 50Hz and 60Hz are "about 100Hz". It seems the author was just speaking in generalities. Can you provide a link to where you got that quote? Thanks.

It is from six easy pieces by Feynman. It is mentioned that 100Hz or cycles/sec is electrical disturbance and behaves as field.
So that means it’s usually 50-60hz but at the time of power surge it goes 100hz(100 cycles/sec).

 

[berkeman]

So that means it’s usually 50-60hz but at the time of power surge it goes 100hz(100 cycles/sec).

No, I don't think that's what they are saying. I don't have a copy of that book, so it's hard for me to guess what was being said.

 

[rudransh verma]

No, I don't think that's what they are saying. I don't have a copy of that book, so it's hard for me to guess what was being said.

 

[berkeman]

Yeah, he's just talking about approximate AC Mains line frequencies being on the order of 100Hz. See how he is using orders of magnitude to describe the other bands? It's just an unfortunate choice of words to call AC Mains line frequencies "disturbances".

 

[rudransh verma]

Yeah, he's just talking about approximate AC Mains line frequencies being on the order of 100Hz. See how he is using orders of magnitude to describe the other bands? It's just an unfortunate choice of words to call AC Mains line frequencies "disturbances".

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I thought it’s usually 50-60 cycles but when there is Voltage increase or power surge then it goes up to 100 and we get dangerous fields generated around the circuits. That is disturbance. What do you think?

 

[berkeman]

I thought it’s usually 50-60 cycles but when there is Voltage increase or power surge then it goes up to 100 and we get dangerous fields generated around the circuits. That is disturbance. What do you think?

Nope. I've worked with AC Mains a lot and also with powerline Surges (like due to lightning), and the powerline frequency does not change. As @.Scott said early on -- changing the AC mains frequency would have all kinds of other problems.

The frequency of the power supplied by electric utilities is very regulated. Anything that changes the 50Hz or 60Hz power by more than 0.5Hz is likely to kill the power completely.

More common are short-term "Swell" and "Sag" of the line voltage, which can cause other problems. There is a tremendous amount of inertia behind the AC Mains line frequency for it to change in response to a "disturbance".

 

[rudransh verma]

Nope. I've worked with AC Mains a lot and also with powerline Surges (like due to lightning), and the powerline frequency does not change. As @.Scott said early on -- changing the AC mains frequency would have all kinds of other problems.
More common are short-term "Swell" and "Sag" of the line voltage, which can cause other problems. There is a tremendous amount of inertia behind the AC Mains line frequency for it to change in response to a "disturbance".

So the author is talking about the same 50-60 hz(cycles) and is mentioning it as 100 and he is calling it disturbance and is saying it is a field.
50-60 or 100 are all almost same.

 

[berkeman]

50-60 or 100 are all almost same.

Yes, see how he lists other frequency bands as orders of magnitude?

he is calling it disturbance and is saying it is a field.

Yes, as I said the term "disturbance" is unfortunate. I'm guessing he said that because the AC Electric and Magnetic fields from AC Mains wiring are "parasitic" in the sense that they are not used for anything. They are a result of the voltages and currents in the wires, not part of a communication system like the other "Waves" that he lists.

 

[rudransh verma]

Yes, see how he lists other frequency bands as orders of magnitude?Yes, as I said the term "disturbance" is unfortunate. I'm guessing he said that because the AC Electric and Magnetic fields from AC Mains wiring are "parasitic" in the sense that they are not used for anything. They are a result of the voltages and currents in the wires, not part of a communication system like the other "Waves" that he lists.

Yes it’s the current we use and the fields it creates around the wires are of no use and are disturbances.
One thing I’m not clear about.
The usual pickup that we get from electric currents in the circuits in the walls of the building has a frequency of about 100 cycles/sec.
Overall it is saying 100hz is the frequency of AC. Right?
If we increase the AC frequency and the wires can withstand the current then it would create strong fields around wires which could damage nearby appliances. The ends of the wire would create sparks by ionising the air.

 

[berkeman]

Overall it is saying 100hz is the frequency of AC. Right?

The common AC Mains frequencies are 50Hz and 60Hz, which are on the order of 100Hz.

If we increase the AC frequency and the wires can withstand the current then it would create strong fields around wires which could damage nearby appliances. The ends of the wire would create sparks by ionising the air.

No. There are a number of appliances and devices that use AC Mains power that would not tolerate much of an increase in frequency. Obvious ones are clocks that use the AC Mains frequency as a reference, and motors that rely on the AC Mains frequency to run synchronously with. The bigger safety risk is with AC Mains transformers -- they typically use laminations in their construction (Google search terms in bold) to limit thermal losses due to eddy currents.

The thickness of the laminations is set by the 50/60Hz line frequency, and if you go a lot above that, you get lots more losses due to heat and potentially a bad overtemperature failure of the transformer. (Please don't ask me about the time that I inadvertently set the AC Mains generator for a test setup to 400Hz instead of 60Hz and fortunately smelled the melting transformers before they caught fire in the lab...)

 

[davenn]

Overall it is saying 100hz is the frequency of AC. Right?

No, you seem fixated on this and constantly repeating it, it is incorrect

In SOME countries, the mains frequency is 50Hz -- Australia (where I am) and New Zealand are a couple of them
In OTHER countries the mains frequency is 60Hz

As @.Scott said earlier, the mains freq. which ever is used, is very strongly controlled and it's variation would be 0.5Hz or less.

 

[davenn]

You mean pickup is the shock we receive on touching a bare wire!

No, it's the frequency "picked up" ( received) by test equipment

 

[hutchphd]

The common AC Mains frequencies are 50Hz and 60Hz, which are on the order of 100Hz.

It is a little more definite than that. If you run a 50Hz current through a resistor the power fluctuation goes like $sin^2$ which doubles the frequency. That is why the fluorescent lights ( in the UK) flicker at 100 Hz: current going either direction makes light. An arc will put out RF modulated at 100 Hz. for the same reason.
So the interference is often the power delivered and the author was being exact

 

[rudransh verma]

It is a little more definite than that. If you run a 50Hz current through a resistor the power fluctuation goes like $sin^2$ which doubles the frequency. That is why the fluorescent lights ( in the UK) flicker at 100 Hz: current going either direction makes light. An arc will put out RF modulated at 100 Hz. for the same reason.
So the interference is often the power delivered and the author was being exact

@davenn In India it’s 50hz.

 

[rudransh verma]

You will get either 50 or 60Hz.
It says "about 100 cycles per second". Given a spectrum that runs from below vertical sync rates (30 Hz) to beyond gamma rays, 50 Hz is "about" 100 Hz.

Sorry yesterday I was a little tense. But now I got you. You are saying the author is talking about same 50-60 hz but referring it as about 100. They are all same roughly. This current in wires make fields which he called as electrical disturbance.
Imagine somehow it’s frequency is increased to a dangerous level. After destroying electrical appliances there would be huge fields around the wirings. We would see sparks in which is actually ionising the air.