I've a problem understanding this monophased rectifier (I'm not sure it's called a rectifier in english).



It says Vab = Vam - Vbm. I don't get why it's not Vab = Vam + Vbm and the arrow Vbm should be going upward instead of downward.
And also why Vam = E.sin.(ωt)?

I can translate the text if needed but I guessed the picture was self-explanatory.

Thanks in advance.

 

Do yo know what ground (reference point) is ??
http://forum.allaboutcircuits.com/showpost.php?p=485862&postcount=14
And for your circuit the ground is at point M.

As for the " Vam = E.sin.(ωt)?" - transformer don't work in DC. So we need AC voltage to force transformer to work.

 

I've a problem understanding this monophased rectifier (I'm not sure it's called a rectifier in english).



It says Vab = Vam - Vbm. I don't get why it's not Vab = Vam + Vbm and the arrow Vbm should be going upward instead of downward.
And also why Vam = E.sin.(ωt)?

I can translate the text if needed but I guessed the picture was self-explanatory.

Thanks in advance.

The two voltages Vam & Vbm at any given time are opposite polarity as referred to "M" which is the centre tap.
Hence one voltage is given a negative sign.(this is completely arbitrary,they could have chosen either one)

If you subtract a minus,you end up with a positive,so the amplitude of Vab turns out to be exactly what you would expect.(Vam+Vbm)

They need to emphasise the different signs of Vam & Vbm to help explain how a Fullwave rectifier using a centre-tapped transformer works.