Transformers & Phase Difference

In summary, the phase differences that take place with an ideal transformer involve an alternating flux that is in phase with both the primary and secondary coils. According to Faraday's Law, the induced emf in the secondary coil will be 90 degrees out of phase with its flux. The back emf in the primary coil will also be 90 degrees out of phase and in phase with the emf in the secondary coil. However, when a load is connected to the secondary, mutual and self induction can alter the phase differences and the secondary current may be pi out of phase with the applied emf. The mathematical calculations for these variations are straightforward.
  • #1
Freddy86
17
0
Hi, I'm trying to figure out what phase differences take place with an ideal transformer. This is what I have figured out so far:

If you apply an AC current to the primary coil then you will get an alternating flux in the primary and secondary coils simultaneously therefore the fluxes are in phase. The induced emf at the secondary will be 90 degrees out of phase to its flux which follows on from Faraday's Law. I'm trying to figure out the phase differences of the back emf's. Will the back emf in the primary coil also be 90 degrees out of phase and therefore be in phase with the emf of the secondary? I'm not sure about the back emf of the secondary? Is there anything that is 180 degrees out of phase?

Thank you for any help given.
 
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  • #2
I was under the impression that transformers were a 180 degree phase shift, as the currents match up but the sign gets reversed. The primary is just an inductor if you take away the secondary though, so the current trails voltage by a quarter cycle, which is a -90 degree phase shift. The secondary is the same way, however, there's something in Faraday's law which changes the sign so that it's 180 rather than 0. It's been a while though, so someone double check me.
 
  • #3
Freddy86 said:
Will the back emf in the primary coil also be 90 degrees out of phase and therefore be in phase with the emf of the secondary?

Yes. But this is as long as we confine ourselves to emfs arising from rate of change of primary current. The fun starts when we also have a varying current in the secondary because we have connected a load across it. We then get another emf induced in the primary (mutual induction) and another in the secondary (self induction). This alters things quite a lot. When certain reasonable approximations are made, the secondary current does indeed turn out to be pi out of phase with the applied emf. The maths is surprisingly straightforward.
 

1. What are Transformers and Phase Difference?

Transformers are electrical devices used to transfer energy between two or more circuits through electromagnetic induction. Phase difference refers to the difference in phase between two or more alternating currents or voltages.

2. How do Transformers work?

Transformers work by using two coils of wire, known as the primary and secondary windings, wound around a common iron core. When an alternating current flows through the primary winding, it creates a changing magnetic field which induces a voltage in the secondary winding. This voltage can then be transformed to a higher or lower value depending on the ratio of the number of turns in the primary and secondary windings.

3. What is the purpose of Transformers?

The main purpose of Transformers is to transfer electrical energy between circuits with different voltage levels. They are commonly used in power distribution systems to step up or step down voltage levels for efficient transmission and distribution of electricity.

4. What is the significance of Phase Difference in Transformers?

In Transformers, phase difference is important because it determines the direction and magnitude of the induced voltage in the secondary winding. When the two currents have the same phase, the transformer is said to be in-phase and the output voltage will be at its maximum. However, if the two currents have opposite phases, the transformer is said to be out-of-phase and the output voltage will be at its minimum.

5. How is Phase Difference measured in Transformers?

Phase difference can be measured using a device called a phase meter or by using an oscilloscope to compare the waveforms of the two currents. The phase difference is usually expressed in degrees or radians and can range from 0° to 180°. A phase difference of 0° means the two currents are in-phase, while a phase difference of 180° means they are completely out-of-phase.

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