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Middle School Electrical Transformer Definition

09/21/2017 10:42 PM

I'm writing a poster for middle school kids explaining how electricity is changed from 480 volts to 120 for classroom use. I was wondering who I could ask and then realized I had this great forum I could ask. Please check my work,

"Transforming Electric Current

How does the 480 volts coming from the electric pole and solar panels get reduced to 120 volts for use in classrooms? Electrical current can be compared to a river, where volts are the width of the river and amps are the flow.

In a transformer, the primary wire carrying a 480 volt / 4 amp alternating current is coiled to generate a fluctuating magnetic field. An electrical current is then induced in a secondary coil placed in the field. If the secondary coil has 1/4th the number of turns of the primary, the current induced in it will be 1/4th the voltage at 4 times the amperage: 120 volt / 20 amp.

Our transformers are 33% more efficient because they use heavier wire and more turns in each coil. They also give off less heat, reducing air conditioning requirements."

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Guru

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#1

Re: Middle school electrical transformer definition

09/21/2017 11:47 PM

Flow is good as an analogy for amps. However, river width is essentially equivalent to flow. The best analogy for voltage is pressure, which is not particularly related to width.

Whose transformers are are less efficient than yours; why; and where do you get the 33% figure?

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#23

Re: Middle school electrical transformer definition

09/26/2017 2:14 PM

Thanks for the suggestion. I'll change the copy to improve the comparison.

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#2

Re: Middle school electrical transformer definition

09/22/2017 4:31 AM

BTW, 33% more efficient means your transformer is 33% bigger and 33% more expensive than the ones you are comparing them with.

Moreover, you are wrong in assuming that "reducing the air conditioning requirements will have any effect" on the price, since most line frequency transformers are designed for natural convection, which is free.

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#8

Re: Middle school electrical transformer definition

09/22/2017 10:58 AM

That's a great idea. Thanks.

I'll have to look into more of the facts about the brand of transformer. It probably over states the percentage, I'll probably just say its high performance transformer, using better wire.

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#3

Re: Middle school electrical transformer definition

09/22/2017 5:46 AM

This doesn't fully answer your question but I remember many many years ago while trying to understand electrical questions in a physics class a mate of mine said imagine plumbing. The water in the pipes is your current, the pressure from the header tank or mains supply is your voltage and the pipes are what creates the resistance. You can also visualize ohms law easily with this analogy.

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#9

Re: Middle school electrical transformer definition

09/22/2017 10:59 AM

Thanks for the suggestion, I'll use it.

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#4

Re: Middle School Electrical Transformer Definition

09/22/2017 7:55 AM

It best to do a hands on project where the kids build some demonstration models, this leads to a greater understanding of what's taking place and how these things work....

Kits for classroom demonstration are sold everywhere....

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#10

Re: Middle School Electrical Transformer Definition

09/22/2017 11:08 AM

Thanks, that's a great video.

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#5

Re: Middle School Electrical Transformer Definition

09/22/2017 9:04 AM

I think a lever is a better analogy. Force is analogous to voltage and motion is analogous to current. On the high voltage side (closer to the fulcrum) there is less current (motion) and more voltage (force). On the low voltage side, there is less voltage (force) and more current (motion).

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#11

Re: Middle School Electrical Transformer Definition

09/22/2017 11:09 AM

Thanks. That's a good analogy.

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#14

Re: Middle School Electrical Transformer Definition

09/22/2017 12:14 PM

That is why voltage is sometimes referred to as e.m.f. (emf) electro-motive force.

Water flow (I feel) is a just OK analogy, but a river might have a seriously large amount of flow (Amazon), with an almost unnoticeable current.

Current ties right in with the speed analogy, whether it is liquid speed of movement, or solids moving, or a stationary system with balanced moments of weight on lever arms as presented above. Current (speed of electrical flow), also ties in with how fast water current turns a given water wheel, completing the analogy of power.

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#22

Re: Middle School Electrical Transformer Definition

09/26/2017 1:33 PM

You're sort of right. Current is coulombs/sec, not distance/sec. The wider the wire/river, the slower the distance/sec is needed to carry the same coulombs(water molecules)/sec.

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#6

Re: Middle School Electrical Transformer Definition

09/22/2017 9:09 AM

Thanks for your feedback. It helps a lot.

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#7

Re: Middle School Electrical Transformer Definition

09/22/2017 9:53 AM

"In a transformer, the primary wire carrying a 480 volt / 4 amp alternating current is coiled to generate a fluctuating magnetic field. An electrical current is then induced in a secondary coil placed in the field. If the secondary coil has 1/4th the number of turns of the primary, the current induced in it will be 1/4th the voltage at 4 times the amperage: 120 volt / 20 16 amp."

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#12

Re: Middle School Electrical Transformer Definition

09/22/2017 11:10 AM

Thanks, I'll use those numbers.

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#13

Re: Middle School Electrical Transformer Definition

09/22/2017 12:08 PM

Are you sure this information blurb is using up to date information?

What does the National Electrical Code have to say about wiring power to public schools?

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#18

Re: Middle School Electrical Transformer Definition

09/22/2017 10:56 PM

I'll check into it. Thanks for your thoughts.

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#15

Re: Middle School Electrical Transformer Definition

09/22/2017 3:37 PM

Please post a picture of your final version and let us know how the students reacted--especially what questions they asked.

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#16

Re: Middle School Electrical Transformer Definition

09/22/2017 3:40 PM

I will. Thanks.

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#17

Re: Middle School Electrical Transformer Definition

09/22/2017 8:37 PM

Why on earth would a middle schooler care about the efficiency of your transformers? Most adults, even those IN the electrical field, have almost no grasp on what transformer efficiency even means.

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#19

Re: Middle School Electrical Transformer Definition

09/22/2017 10:58 PM

The school is near net-zero. Every little bit helps. The signage project covers every aspect of the school's energy system. Thanks for the feedback.

Commentator

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#20

Re: Middle School Electrical Transformer Definition

09/25/2017 3:40 PM

Your definition is around the wrong way.
Voltage can be talked about as 480v on the primary will produce 120v on the secondary.
But with current the way to describe it is this:

When 20 amps flows in the secondary, 5 amps will flow in the primary. (The losses will be about 5%).

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#21

Re: Middle School Electrical Transformer Definition

09/25/2017 3:51 PM

Thanks for the correction.

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#24

Re: Middle School Electrical Transformer Definition

10/05/2017 7:43 AM

One way of explaining the school students could be through example of mechanical gear system. Two wheels having different number of teeth (and therefore different diameters like different conductor diameter in two windings). Here number of teeth could be compared with number of turns in transformer winding. Total work done (total power ) is same except for the friction (iron and copper loss). Less number of turns would have more number of revolutions (less number of turns would have more voltage per turn.) and vice versa. Total work done would be the product of torque and number revolution (product of voltage and current). This will be same for both sides in transformer as well as in turning gear system.

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#25

Re: Middle School Electrical Transformer Definition

10/05/2017 11:06 AM

Thanks for the suggestion. I may use it.

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#26

Re: Middle School Electrical Transformer Definition

10/06/2017 5:23 AM

The example for gears could be bicycle where one revolution of paddle wheel gear (bigger) results in many revolutions of rear axle wheel (smaller). Since bicycle is a day to day affair for students quite possibly them may understand the subject better.

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#27

Re: Middle School Electrical Transformer Definition

10/06/2017 8:57 AM

That's a great idea. Thanks!

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