Transformer

嗯..我會咁理解...我一步步解你聽. 我打英文，因為咁快d，唔好介意。

1) The fundamental principle of transformer is the magnetic flux coupling. the magnetic flux generated in the primary coil will be coupled to the secondary coil. Using soft-iron core can make the coupling of flux better. Different kinds of core have different effects on coupling.

2) however, the coupling is always imperfect. there are some leakage flux across the primary and the secondary coils.

3) 小空隙 means air-gap. you have to know thta adding air-gap can prevent core-saturation. however, it may cause a drop in efficiency, one of the reasons is that you artificially add an gap there and it may depreciate the coupling of flux.

4) depreciation of coupling leads to energy loss, i.e. not all energy stored in the primary coil flux can be coupled to the secondary winding.

5) however, adding an air-gap is an usual practice. I made a transformer before. Without air-gaps, the transformer may easily suffer from core saturation which is more troublesome than having a lower efficiency.

6) To understand what core saturation is, you have to know more about the magnetization loop and B-H curve. but that's off your question..I am not going to type here.

7) Last but not least, i want to mention about the magnetization loss. for core without air-gaps, normally the magnetization loss is smaller as told by the BH curve.

Adding air-gaps can decrease the magnetizing inductance and also increase the magnetization loss. That's why adding air-gaps may decrease the efficiency.

I hope I can help you

錯,咁樣會有leakage of magnetic flux in soft iron, transformer既efficiency係會下降先arm