Transformer concepts (magnetic induction)

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Homework Help Overview

The discussion revolves around the concepts of transformers, particularly focusing on the transformer equation and the effects of circuit configurations on current and magnetic fields. Participants explore the implications of an open-circuit secondary coil and how it influences the primary coil's current and magnetic field generation.

Discussion Character

  • Conceptual clarification, Assumption checking, Exploratory

Approaches and Questions Raised

  • Participants question how opening the secondary circuit affects the primary current and whether a lack of current in the secondary can still produce a magnetic field. There are discussions about the relationship between secondary current and primary current, and how changes in one affect the other.

Discussion Status

Some participants provide insights into the dynamics of current flow in the primary coil when the secondary coil is open-circuited, noting that the primary still produces a magnetic field. Others express a growing understanding of the concepts discussed, indicating a productive exchange of ideas.

Contextual Notes

Participants are navigating complex concepts related to transformer operation, including assumptions about ideal conditions and the effects of resistance in the coils. There is also mention of power loss calculations in high voltage transmission, which introduces additional considerations into the discussion.

Terocamo
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Homework Statement


The transfromer equation is given by\frac{Vp}{Vs}=\frac{Np}{Ns} for an ideal transformer.
This equation is correct only if there are perfect flux linkage, the resistance of both primary and secondary coil is small and carries negligible current.
The notes mention here if the secondary coil is in open-circuit, the latter requirement about resistance is well met.

However I don't understand how opening the circuit of secondary coil will affect the current in the primary coil. Also if there is no current in the secondary coil, can it produce magnetic field?
 
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Terocamo said:

Homework Statement


The transfromer equation is given by\frac{Vp}{Vs}=\frac{Np}{Ns} for an ideal transformer.
This equation is correct only if there are perfect flux linkage, the resistance of both primary and secondary coil is small and carries negligible current.
The notes mention here if the secondary coil is in open-circuit, the latter requirement about resistance is well met.

However I don't understand how opening the circuit of secondary coil will affect the current in the primary coil. Also if there is no current in the secondary coil, can it produce magnetic field?

if the secondary coil is in open-circuit, the resistance of primary winding still affects the flow of current and Ip will not be 90 deg with Vp.

if secondary circuit is opened, current still flows in primary and it will produce magnetic field which is responsible for Vs
 
n.karthick said:
if the secondary coil is in open-circuit, the resistance of primary winding still affects the flow of current and Ip will not be 90 deg with Vp.

if secondary circuit is opened, current still flows in primary and it will produce magnetic field which is responsible for Vs

Can you explain in more detail about how the secondary coil affect the current and power of the primary coil?
 
If secondary current flows (or increases) in a transformer, it creates (more) flux which is opposite to flux created by primary current. Hence the resultant flux is reduced momentarily. But the primary coil immediately draws more current from source to produce same amount of flux so that Vp (voltage across primary) is unaltered. Since current from source is increased, now source is supplying power to the transformer which is in turn transformed to secondary.
 
n.karthick said:
If secondary current flows (or increases) in a transformer, it creates (more) flux which is opposite to flux created by primary current. Hence the resultant flux is reduced momentarily. But the primary coil immediately draws more current from source to produce same amount of flux so that Vp (voltage across primary) is unaltered. Since current from source is increased, now source is supplying power to the transformer which is in turn transformed to secondary.

Thz, I think I finally understand now, it is very helpful.
 
I have another problem. Why is the equation P=V^2/R not used to calculate the power loss in high voltage transmission cables? And why is I^2R okay to use?
 
Terocamo said:
I have another problem. Why is the equation P=V^2/R not used to calculate the power loss in high voltage transmission cables? And why is I^2R okay to use?

You can use both but in P=V^2/R, V is the voltage drop in transmission cable and not the transmission voltage. I prefer I^2R since if I measure the current I can find the loss.
 

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