Transformer Efficiency Problems

[BlackMelon]

Hello,

My friend designs a special transformer, believing that its efficiency will rise and voltage regulation will fall compared to an ordinary one . He did a test with the same resistive load and got results below:

T1(ordinary) Vp=220V 50Hz AC Vs(nl) = 99.8V Vs(fl) = 92.8V Pin = 129W Pout =92.8W
T2(special) Vp=220V 50Hz AC Vs(nl) = 99.8V Vs(fl) = 96.7V Pin = 130W Pout = 96.7W

where:
Vp: Primary voltage
Vs: Secondary voltage
Pin: Input power from a 220V source. (household outlet)
Pout: Output power at a load
All voltages are in RMS

He expected that the input complex power(Sin) of the special transformer should be 100VA with an efficiency of 90%.
However, the Sin is actually 130VA and the efficiency is about 74.38%. What is the cause of this event?

Thank you
BlackMelon

 

[jim hardy]

What is the cause of this event?

A question well stated is half answered.
You're asking us to guess .
Okay -
Excerpting from your post -

He expected that the input complex power(Sin) of the special transformer should be 100VA...
Pin = 130W... However, the Sin is actually 130VA

Sin and Pin should differ by magnetizing VA. So,
My guess is somebody doesn't know the difference between a volt-amp and a watt.

I cannot can figure out your riddle from what you've given us.

 

[anorlunda]

http://www.brighthubengineering.com/diy-electronics-devices/96783-designing-your-own-transformer/

That link may give some advice, and also formulas and tables used to calculate the performance of the design.

Transformer design is not easy.

 

[BlackMelon]

Hardy, I agree with you. The current source should supply core loss resistance with a real power, magnetizing inductance with a reactive power, and a leakage inductance with a reactive power also. I mean even without a resistive load, there should be both real and reactive.

The experiment of my friend is strange. The 130VA of a voltage source is purely from a wattage. I ask him twice before posting this.

Also,Neumaier, thank you for the information. I will tell my friend to read this carefully.