# Transformer core variable reluctance

• sondreL
In summary, the conversation discusses the potential for creating secondary induction in a transformer by varying the reluctance, or permeability, of the core while DC is applied to the primary. The group agrees that this would result in an induced current and compares it to a reverse magnetic amplifier. They also mention how this principle is used in automobiles for measuring rotation rates.

#### sondreL

Hi , When DC is applied to a transformer there is no secondary induction because DC current creates no changing flux in the Core. If I could change the reluctance, or permeability is another word I guess, of the transformer core while still having DC applied to the primary , would that then result in a secondary induced current?

Yeah, I think so. What matters in the end is the magnetic flux that is encompassed by the secondary coils and the change of that flux; whether you change that total flux by modulating the external magnetic field or by changing the inductance of the coil shouldn't matter.

Ok , can anyone else please confirm, would having DC on the transformer primary and then somehow varying the reluctance of the core result in induced secondary , I myself think it should the above poster rumborak also said so. It would turn out as a reverse magnetic amplifier , since mag amps work on having AC as the load on primary and DC as the control current for more or less core saturation. Also if I could change the reluctance of the core while DC is applied to the primary inducing changing flux in the secondary how would this affect the DC in the primary from the perspective of the incoming DC ?Normally when I apply DC to a transformer nothing happens just the winding heats up slowly , what would happen here ?

I think it's worth asking the question of how you plan to change the reluctance of the secondary coil? The only way I can imagine is a) by changing the area the magnetic circuit encompasses or b) changing the number of windings. In both cases it should result in an induced voltage.

This very principal is used in many automobiles for sensors that measure the rate of rotation of things like the crankshaft, wheels, transmission gears, etc. A coil of wire is wrapped around a permanent magnet. A gear rotates through the magnetic field. The permeability changes as the teeth of the gear move toward and away from the sensor, this induces an AC voltage in the coil. A circuit in the cars computer measures the frequency of the signal and tells the computer how fast the component is rotating.

## 1. What is transformer core variable reluctance?

Transformer core variable reluctance is a term used to describe the ability of a transformer's core material to change its magnetic flux density in response to changes in the applied voltage or current. This phenomenon is crucial in the operation of transformers, as it allows for efficient and precise control of energy transfer between two circuits.

## 2. How does variable reluctance affect transformer performance?

The variable reluctance of a transformer's core material can significantly impact its performance. If the core material has a high reluctance, it will require more turns of wire in the transformer's primary and secondary coils to achieve the desired level of energy transfer. On the other hand, a low reluctance core material will require fewer turns of wire, resulting in a more efficient transformer.

## 3. What materials are commonly used for transformer cores with variable reluctance?

The most frequently used material for transformer cores with variable reluctance is laminated silicon steel. This material has high magnetic permeability, low hysteresis losses, and low electrical conductivity, making it ideal for transformer applications. Other materials such as nickel-iron alloys and ferrites may also be used, depending on the specific requirements of the transformer.

## 4. How is variable reluctance controlled in transformers?

Variable reluctance in transformers is controlled by varying the amount of current flowing through the primary winding, which in turn changes the strength of the magnetic field. This change in magnetic field induces a voltage in the secondary winding, resulting in energy transfer between the two circuits. Additionally, the design of the core material and the number of turns in the primary and secondary coils can also affect the variable reluctance of a transformer.

## 5. What are the advantages of using variable reluctance in transformers?

The use of variable reluctance in transformers offers several advantages, including improved energy efficiency, lower losses, and greater control over the energy transfer between circuits. It also allows for the reduction of size and weight of the transformer, making it more compact and cost-effective. Additionally, variable reluctance can help reduce noise and vibration in transformers, making them more suitable for sensitive applications.

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