# Transformer Frequency: No Relative Motion Explained

• ranju
In summary: Suppose you apply an AC current through the first coil and measure the voltage across the second coil. The voltage across the second coil will be the same as the voltage across the first coil, but the current through the first coil will have changed because the first coil is passing the current through it.
ranju
We know that frequency of induced emf in secondary coil remains same as frequency of applied voltage in primary coil and I have read that its reason is " there is no relative motion between the coils..".
Actually I am not getting the reason , maybe some fact or concept has slipped from my mind but I can't recollect how frequency is dependent on relative motion between the coils..

Consider a bar magnet rotating in a fixed DC magnetic field. From the magnet's point of view, the field appears to be an AC field with a frequency the same as the rotational frequency of the magnet. In an analogous way, visualize a transformer with the secondary coil rotating. To the secondary, the frequency of the apparent magnetic field has a frequency equal to the difference between the AC frequency and the frequency of rotation of the coil.

Of course we don't rotate the secondary coil of things we call transformers. When we do rotate one of the coils, we call the devices generators or motors. That is far from the full story of how generators or motors work, but it is an important clue.

ranju and berkeman
ranju said:
We know that frequency of induced emf in secondary coil remains same as frequency of applied voltage in primary coil and I have read that its reason is " there is no relative motion between the coils..".
Actually I am not getting the reason , maybe some fact or concept has slipped from my mind but I can't recollect how frequency is dependent on relative motion between the coils..
Frequency of induced emf in the secondary coil is the same as the frequency of the voltage applied to the primary coil is the same as frequency of magnetic flux coupling the windings. By Faraday law of electromagnetic induction : emf = N⋅dφ/dt. No relative motion between parts* of transformer, transformer is the "static" converter of electromagnetic energy.

* small vibrations of turns and other parts can be neglected

sorry But I did'nt get your point..!

ranju said:
sorry But I did'nt get your point..!
Then, I believe you don't understand Faraday's law of em induction.

zoki85 said:
No relative motion between parts* of transformer, transformer is the "static" converter of electromagnetic energy.
this is the point I am not getting...!
I know law of electromagnetic induction but I am not able to relate it here..

ranju said:
this is the point I am not getting...!
I know law of electromagnetic induction but I am not able to relate it here..
If you know that law and know the fact that parts of a classic transformer don't move (they are static), why did you mention movement between coils:
ranju said:
Actually I am not getting the reason , maybe some fact or concept has slipped from my mind but I can't recollect how frequency is dependent on relative motion between the coils..Please clear it out..
?

You did'not get what I was intended to ask.. actually I actually wanted to know the relation between the frequency and movement of coils.. how frequency is dependent on it.. Here , there is no relative motion between coils , hence frequency is constant as stated. But what is the reason ??

ranju said:
You did'not get what I was intended to ask.. actually I actually wanted to know the relation between the frequency and movement of coils.. how frequency is dependent on it.. Here , there is no relative motion between coils , hence frequency is constant as stated. But what is the reason ??

In post number 2, I showed you a kind of relative motion could change the apparent frequency. Did you understand that?

ranju said:
You did'not get what I was intended to ask.. actually I actually wanted to know the relation between the frequency and movement of coils.. how frequency is dependent on it.. Here , there is no relative motion between coils , hence frequency is constant as stated. But what is the reason ??
If the coils rotate/move one to each other and at least one is passed by current i(t)≠0 you'll have so called:

1. emf of rotation (frequency of which, fr, coincides with frequency of mechanical rotation/motion)
2. emf of transformation (freq. of which, ft, coincides with frequency of the current)

Total voltage is the supereposition of two emfs.

As a pair of examples, imagine this:
1. Two solenoidal coils are placed parallel, on directly above the other. Now, if you apply an AC current through the top solenoid, i=sin(wt), then it will produce a time varying magnetic field, phi = some_constant sin(wt).
Some of the top solenoid's field will cut into the second solenoid. Assuming the second solenoid isn't tied to a load, it will have a voltage induced based upon the change in magnetic field, dphi / dt, or V_coil2 = some_other_constant cos(wt).

Both coils are running at w (frequency)

2. Assume the top solenoid (from 1 ) had a steady DC current going though it. If the two solenoids are still, the amount of field induced in the second coil will be steady and dphi / dt = 0, no voltage is across the second coil.
However, if the top coil begins to rotate at some rate, wr, then there is a voltage induced in the second solenoid at V_coil2=a_constant cos(wrt) as the flux from the top solenoid begins to rotate.

ranju

## 1. What is transformer frequency?

Transformer frequency refers to the rate at which the alternating current (AC) changes direction in a transformer. It is measured in hertz (Hz) and is typically 50 or 60 Hz in most countries.

## 2. How does transformer frequency affect the performance of a transformer?

The frequency of an AC power source affects the efficiency and output of a transformer. Higher frequencies can cause increased power losses and decreased output, while lower frequencies may result in overheating and damage to the transformer.

## 3. What is meant by "no relative motion" in transformer frequency?

No relative motion in transformer frequency means that the primary and secondary coils of the transformer are stationary in relation to each other. This is in contrast to transformers with rotating parts, which have a relative motion between the coils.

## 4. How is transformer frequency determined?

Transformer frequency is typically determined by the power grid frequency, which is set by the utility company. In some cases, transformers may be designed for specific frequencies, such as in industrial or specialized applications.

## 5. Can transformer frequency be changed?

Yes, transformer frequency can be changed with the use of specialized equipment, such as frequency converters. However, this process can be costly and may not be necessary in most cases, as the frequency of the power grid is typically stable and reliable.

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