Explaining Toroidal Transformers & Their Self-Shielding Properties

In summary, toroidal transformers are known for their self-shielding properties and strong magnetic flux within the core. However, threading a good conductor through the center of the toroid and creating a one-turn secondary can cause a short circuit and a large current flow, despite the wire being in a near-zero field region. This phenomenon is not limited to toroidal transformers and raises questions about current theories. It is explained by Faraday's law, where the oscillating magnetic field in the toroid creates an electric field in the wire. This occurs in the "empty space" within the toroid, rather than the core.
  • #1
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This question relates to 50Hz power toroidal transformers.

Toroidal transformers are well known for their self shielding properties and consequently have a near-zero external field. Most of the magnetic flux lies within the core.
Yet if one where to thread a good conductor through the centre of the toroid and connect the ends to form a loop, thus creating a one-turn secondary, one would in practice cause a short circuit and a very large current would flow (limited by the resistance of the loop).
This seems to imply that the loop is experiencing most of the field created by the primary coil. How can this be explained when the wire itself lies completely in a near-zero field region? Seems spooky to me. This phenomenon is not restricted to toroidal transformers but is at the heart of every electrical machine, just that in a toroidal transformer it becomes plain that current theories and textbooks are missing something big time. The standard answer would be that the emf generated in the secondary depends on the amount of flux “linking” the primary and secondary and in this case all of the flux plainly passes through the area enclosed by the secondary circuit. I just cannot see how this “explanation” explains anything. How do the electrons in the wire feel the primary magnetic field?
 
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  • #2
Maybe I don't understand your setup here, but why would "...wire itself lies completely in a near-zero field region..." when a part of it is threading through the center of the solenoid where the field is the largest? One could easily think of this region as the "emf source" for the secondary to cause current to flow.

Zz.
 
  • #3
There is no B field at the wire, but there is an electric field.
The oscillating magnetic field in the toroid produces an electric field in the wire.
The integral of this field around the circle equals the rate of change of the magnetic flux.
That is Faraday's law.
 
  • #4
To clarify
By centre of the toroid I mean not the core of the toroid, but the empty space of the "window in the doughnut" or the hole in a "Polo" mint. This space is also empty of any field as far as I know at least in an ideal toroidal transformer.
 
  • #5
The E field is in that "empty space".
 

1. What is a toroidal transformer?

A toroidal transformer is a type of electrical transformer that is shaped like a doughnut or torus. It consists of a primary and secondary winding wrapped around a magnetic core made of a ferromagnetic material.

2. How does a toroidal transformer work?

A toroidal transformer works by using electromagnetic induction to transfer electrical energy between the primary and secondary winding. When an alternating current flows through the primary winding, it creates a changing magnetic field in the core which induces a current in the secondary winding.

3. What are the advantages of using a toroidal transformer?

Some advantages of toroidal transformers include their compact size, high efficiency, and low electromagnetic interference. They also have a lower external magnetic field compared to other transformer types, making them ideal for sensitive electronic equipment.

4. What are self-shielding properties of toroidal transformers?

Self-shielding properties refer to the ability of a toroidal transformer to reduce the amount of electromagnetic interference it produces. This is due to the toroidal shape of the transformer, which allows the magnetic field to be contained within the core, resulting in less interference with other nearby electronic devices.

5. How are toroidal transformers used in different applications?

Toroidal transformers are used in a variety of applications, including power supplies, audio equipment, and medical devices. They are also commonly used in household appliances, such as refrigerators and washing machines, due to their compact size and low noise level.

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