IF that generator on the truck is ever used to power any aircraft electronics, like a radio to contact aircraft, it might need to use 400 Hz for an aircraft type radio. Or if it is powering an aircraft flux-gate compass, or mini-cannon. ORit might be that only that generator was available.

 

400Hz and 50/60Hz Generators also operate at substantially different standardized Voltages.

As far as I know, ( which might not be very far in this case ).

400Hz Generators are usually 3-Phase,
Single-Phase would be a very unusual application,
400Hz Generators are exclusively for specialized Military applications.

50/60Hz Generators may be Single-Phase or 3-Phase,
or even both at the same time,
depending upon the requirements of the intended application.

The standard 400 Hz AC system used by aircraft has a phase voltage of 115 V.

400 Hz systems are used well beyond specialized military applications. Not only are aircraft, military, commercial, and private, that are complex enough to need an AC system almost always 400 Hz, but so are many other mobile systems such as ships and for the same reasons -- power-to-weight considerations.

 

Hi, I suggest using an analogy that most people are already familiar with, even if they don't know how to explain it: Sound pitch and wave interference.

Open this link and play the tone at 440Hz. Next open a new window and play an additional tone of 440Hz at the same. You'll hear the same pitch / note of A as both frequencies are playing because the pressure differential that the tones generate in air are in phase. This means they travel through the air in a way that doesn't interfere with each other (no destructive interference).

https://onlinetonegenerator.com/

Now set the second tone to play 430Hz. You'll hear an unmistakable pulsing of the two tones at a frequency of 10Hz (440 - 430) known as the beat frequency. The beat frequency is the result of the pressure waves of each tone smashing against each other as they travel through the air. Since both tones are periodic in nature, the frequency mismatch / interference takes up a periodic nature as well, in this case it oscillates at 10Hz.

A very similar phenomena happens when there is a frequency mismatch between a generator outputting say 60Hz and a power tool that is expecting a power source of 60Hz. If the mismatch is great enough, the pulses of energy delivered by the generator end up being reflected back into the generator. This frequency mismatch will vibrate the machinery at the beat frequency just like in the sound pitch example (unless it gets damped / absorbed). The only way to get rid of the beat vibrations is to ensure there is no frequency mismatch. I like this analogy because it all stems from the same phenomena of wave interference.

As for asking why the standard is 50Hz vs 60Hz etc., the simple answer is it's arbitrary. If they want to know more, refer them to the history on generators and physics of travelling waves.

 

Bro if your students dont understand what is the definition of how many times something happens in one second maybe they should switch to baseball..

 

A very similar phenomena happens when there is a frequency mismatch between a generator outputting say 60Hz and a power tool that is expecting a power source of 60Hz. If the mismatch is great enough, the pulses of energy delivered by the generator end up being reflected back into the generator. This frequency mismatch will vibrate the machinery at the beat frequency just like in the sound pitch example (unless it gets damped / absorbed). The only way to get rid of the beat vibrations is to ensure there is no frequency mismatch. I like this analogy because it all stems from the same phenomena of wave interference.

If you feed a 50Hz power tool with 60Hz:
if it is a universal motor (most are) - it won't give a damn. It will just do what it always does.
If it is an induction motor, it will rotate 20% faster. There will be no beat frequency.
It is not aware of what frequency it should be getting. There is no resonant circuit tuned to 50Hz. It's just a coil of wire around a piece of silicon-iron.

 

If you feed a 50Hz power tool with 60Hz:
if it is a universal motor (most are) - it won't give a damn. It will just do what it always does.
If it is an induction motor, it will rotate 20% faster. There will be no beat frequency.
It is not aware of what frequency it should be getting. There is no resonant circuit tuned to 50Hz. It's just a coil of wire around a piece of silicon-iron.

I was referring to impedance matching which is a universal concept across physics. Maybe I should have said transmission lines not motors.

Can you think of a case where a frequency mismatch will cause a piece of machinery to vibrate? If so, why does this occur and how do you determine the vibration frequency?

 

Bro if your students dont understand what is the definition of how many times something happens in one second maybe they should switch to baseball..

That's pretty ignorant. There is an idea that some people can't learn because they are too stupid. But from my experience, most people are horrible with teaching. Just look at the ego in this thread alone. The guy asked for analogies and how many did he get? I'm not saying mine was correct or optimal but at least I gave one and it's open to debate. The point is to teach non-technical students something technical which requires patience and understanding of their limitations.

 

Bro if your students dont understand what is the definition of how many times something happens in one second maybe they should switch to baseball..

Yeah sure, but no one is really giving a good answer as to why we're using the 400 Hz frequency generator to power a radar. A lot of people have said it's because of weight or size of the generator, but thats not it. It's my fault for not giving a detailed explanation of why I wanted the analogy.

 

That's pretty ignorant. There is an idea that some people can't learn because they are too stupid. But from my experience, most people are horrible with teaching. Just look at the ego in this thread alone. The guy asked for analogies and how many did he get? I'm not saying mine was correct or optimal but at least I gave one and it's open to debate. The point is to teach non-technical students something technical which requires patience and understanding of their limitations.

Thank you, Costanza!

 

Yeah sure, but no one is really giving a good answer as to why we're using the 400 Hz frequency generator to power a radar.

See post #31.

Perhaps you could let us know what it says on the Ratings Plate of the Radar, and that might give us a clue. otherwise it’s complete guesswork.
Like @LowQCab said, always read the specification plate.

 

That's pretty ignorant. There is an idea that some people can't learn because they are too stupid. But from my experience, most people are horrible with teaching. Just look at the ego in this thread alone. The guy asked for analogies and how many did he get? I'm not saying mine was correct or optimal but at least I gave one and it's open to debate. The point is to teach non-technical students something technical which requires patience and understanding of their limitations.

I am sorry if my attitude is somewhat aggressive. If you need an analogy for, for example, the saturation inside n-p-n junction, or accessing registers in an EPROM memory - that I can understand.

If you need an analogy for "how many times something happens in one second", or "10 Hz is if I tap on the table 10 times in a second with equal intervals", as reverse proportional of "this action takes 1/10 second to happen", I am sorry but there is no lower level explanation than this. What is the analogy of 1 + 1? Peter had one apple and Jane gave him one more, how many apples does Peter have now?

I mean (I supposed) you are teaching some high school student, not toddlers... possible future engineers... and of all things to make an analogy you choose EATING BURGERS ?!
come on.......

 

I am sorry but there is no lower level explanation than this.

Aye but that's where you're wrong. Just because it reduces to that in your brain doesn't mean it will to others. Besides, outside of electronics, physics and music, the concept of frequency doesn't really relate to anything. You said how many times something happens in one second? Like what? Punches to the face? If someone doesn't have a background in general physics or music, the concept is nonsensical because there is no reason to count things by the amount of times they happen in one second.

And let's not bullshit each other here. Instead of providing an analogy, you are criticising people you've never met on superficial grounds. On what planet is this not a blatant display of ego and disrespect for your fellow man?

I get upset when I read shit like this because some poor soul will read your post then think to himself something like "I'm too stupid to understand frequency, I might as well give up" and they do. My objective on the other hand is to share my knowledge and plant the seed of interest in science wherever I can. To this end, there are no stupid questions or stupid people only stupid teachers.

 

I provided an analogy, I wrote "10Hz is if I tap on the table 10 times in one second with equal intervals". I think it is super simple and understandable even for someone who encounters the definition of a frequency for the first time.

It was funny to me that someone who is supposed to teach this subject could not come up with an analogy like this, instead he had to ask it on a forum.
I will even be in complete allingment with 2025: I am sorry if my opinion offended anyone.
Even though there wasn't any direct offense in my post, just observation that standards are becoming lower and lower.
Unlike yours, which is full of foul language and accusations towards me.



I am out of this thread.

 

The only sensible analogy for frequency will be RPM, which is even technically correct.
AND certainly there are some who will not be able to understand that. They do not belong in the class about electricity.

 

I missed the question about an analogy for Hertz in particular, but I don't think there is really a use for an analogy in the general sense. And explanation, yes—but an analogy requires some application.

AC (Alternating Current) gets its name from the fact that alternates between positive and negative polarities. It goes from 0V to its peak positive voltage, the back down to its peak negative voltage then back up to 0V. How many cycles each second this happens is expressed in a unit called Hertz—it used to be called cycles per secondI.

The name cycle is from the fact that like a wheel rotating, the true nature of things is a rotary motion, just like the generators that sometimes produce AC. When plotted over time, it describes a sine wave which is the plot you typically see, but that is just a rotation "unrolled".

Hertz can be practically relevant since many things powered by AC use the alternation to cause motion and—for example, 400Hz while make about 6.7 times more opportunities to move than 60Hz.

 

Describing frequency of AC ss an analogy is easy, RPM comes to mind immediately. But finding an analogy that correctly explains why we cannot run a device designed for 400Hz on 60Hz, is not easy.

Look at the absurd analogy I used to explain why we cannot use diesel in an engine designed for gasoline. It does nothing to explain why, and it is comically wrong.

It comes down to this:

1. Frequency has multiple effects on electro-mechanical equipment, such as timing derived from power frequency, saturation of magnetic cores of various components, and the inductive reactance of relay and solenoid coils.

2. Such equipment is designed for one particular frequency. If run at a different frequency, very bad things might happen.

 

My target audience is mainly 18 - 24 year olds that are running on very little sleep, that's why I wanted a break down. They will easily understand frequency, that's not my main point. I wanted to give them a reason as to why the difference in frequency was important from the power source, how it directly applies to the equipment it is powering. I can't share the data plates from the radars, I thought maybe there was some kind of universal answer as to why the manufacturer chose to make this equipment run off a 400 Hz generator instead of 60, so we could use the same generators for all of our equipment. Ya'akov said "400Hz systems are also potentially faster than 60Hz, meaning they are better for high speed actuators and the like", which makes the most sense as an answer to me, because the radars have actuators and other moving parts to make it spin. The analogy isn't necessary with information like that, but i wont be telling my class that information, thats just for my own knowledge now. I will tell my class that I am not an expert on why the choice was made to use 400 Hz, but that they cannot use the 400 Hz power for anything other than the radar (I know they could, but they will not be working with any other 400 Hz equipment in this job), and if they tried to it would damage the equipment. Maybe I will contact the manufacturer and get the answer from them some day. Thank y'all who tried to explain this to me.

 

Describing frequency of AC ss an analogy is easy, RPM comes to mind immediately. But finding an analogy that correctly explains why we cannot run a device designed for 400Hz on 60Hz, is not easy.

Look at the absurd analogy I used to explain why we cannot use diesel in an engine designed for gasoline. It does nothing to explain why, and it is comically wrong.

It comes down to this:

1. Frequency has multiple effects on electro-mechanical equipment, such as timing derived from power frequency, saturation of magnetic cores of various components, and the inductive reactance of relay and solenoid coils.

2. Such equipment is designed for one particular frequency. If run at a different frequency, very bad things might happen.

I thought your horsey analogy was funny, and if it made it stick into someone's head that they cannot use gas in a diesel generator, I would definitely use it in real life. You have to know your audience, and sometimes an over explanation will make them turn off their ears. Some people dont have long attention spans, and we have limited time to teach. If telling them not to hurt the horses will get them to remember the base information DO NOT PUT GAS IN A DIESEL ENGINE, then why not use that analogy?

 

I thought your horsey analogy was funny, and if it made it stick into someone's head that they cannot use gas in a diesel generator, I would definitely use it in real life

If that is what you are looking for, just make sure it is as absurd as my little horses so that none of your students thinks it is the real reason.

 

If that is what you are looking for, just make sure it is as absurd as my little horses so that none of your students thinks it is the real reason.

That's all I am looking for, this one little bit of this job we have broken down so Barney style that anyone can understand it. If anyone has such a lack of nuance that they take it literally, they need to quit this job and go be an electrical engineer lol