Why are the minus signs in the transformer EMF equations N₁dΦ/dt and N₂dΦ/dt?

[Vibhor]

The net flux is the flux set up by the magnetizing current. It is constant as long as the applied voltage (rms) is constant.

If flux is constant , how is EMF induced in the two coils ?

 

[cnh1995]

If flux is constant , how is EMF induced in the two coils ?

RMS value of the flux is constant. Or you can say, the amplitude of the flux waveform is constant.

I think it would - so long as by constant you mean, varying sinusoidally with constant amplitude.
A literally constant flux does not cause any emfs. EMF is always associated with changing flux.

 

[Vibhor]

Ok . I will stop here for the time being

You and @Merlin3189 both have been amazing . Thanks both of you for your time and patience . I really admire the way you both stuck with me in this thread . Some expert members would have been fretting and fuming by now

You might have also been irritated at times . But the good part is that ,you didn't let me know .

People might have more knowledge than you , but few have finer qualities like patience

Keep up the good work .

 

[cnh1995]

This reflected secondary current cancels the secondary mmf.

We have been using this term frequently in this thread, but I think we haven't discussed its another important physical significance.

This reflected secondary current Ip₁ is actually the reflection of the load connected to the secondary.
For a resistive load, the product of applied primary voltage and reflected secondary current gives the power supplied by the source, which is dissipated in the secondary.
Hence,
V_p*I_p1=V_s*I_sec.

Other than maintaining the core flux constant by cancelling the secondary mmf, the reflected load current in the primary is responsible for supplying power (active and reactive) from the source to the load on the secondary.

And thanks for your kind words!