Is the Back EMF of a Transformer a Dynamic Equilibrium?

[haleycomet2]

Why the back emf of the primary coil always equal to the supply voltage but no greater than supply voltage(because of the large number of coil turns) when no loaded?Or it is a kind of dynamic equilibrium?If yes,how it reach equilibrium?

Thank you.

 

[Dadface]

Why the back emf of the primary coil always equal to the supply voltage but no greater than supply voltage(because of the large number of coil turns) when no loaded?Or it is a kind of dynamic equilibrium?If yes,how it reach equilibrium?

Thank you.

It is a simplifying assumption to assume that the back emf and supply voltage are the same.They are not exactly equal because there is a voltage drop across the resistance of the primary winding but usually this can be considered as negligible.

 

[saubhik]

If you apply Kirchhoff's voltage law to primary of the transformer, you get the back emf equal to supply voltage. (neglecting resistance in primary circuit)

 

[haleycomet2]

Under ideal condition(no resistance),since the back emf always equal to the supply voltage,then there would be no current flow through??
If different inductor(different L) is used in the circuit,does the dI/dt would be different even the supply voltage remains the same?

 

[gneill]

Under ideal condition(no resistance),since the back emf always equal to the supply voltage,then there would be no current flow through??
If different inductor(different L) is used in the circuit,does the dI/dt would be different even the supply voltage remains the same?

There would initially be no current. But dI/dt is nonzero, so current will begin to flow according to the appropriate differential equation. The current will increase without bound if there's no limiting resistance; Better make sure there's some resistance in the circuit, or something's going to go FSSST-BANG!

If you change L, then you change the magnitude of dI/dt.

 

[haleycomet2]

ya,i just found it is clear when shown by differential equation.By the way, i am curious that is it possible to map out the trend of the unlimited increase of current?(let V is sin t and L is 1)
Thank you.

 

[gneill]

ya,i just found it is clear when shown by differential equation.By the way, i am curious that is it possible to map out the trend of the unlimited increase of current?(let V is sin t and L is 1)
Thank you.

The worry about infinite increase in current applies to a constant voltage supply (or at least one with a constant, nonzero DC component).

If the supply is a sinewave, v(t) sin(t), then its integral over time is finite. So no blow-up for sinewaves!

 

[haleycomet2]

o...i see,thanks a lot..