94 THE DESIGN OF STATIC TRANSFORMERS 



circuit (G = 1,00) the pressure at the secondary terminals 

 will be 1,5 per cent, lower than at no load. 



The drop in pressure is due to two causes, (1) the resistance 

 of the windings, and (2) the inductance of the windings. The 

 more the primary and the secondary windings are intermixed 

 with one another, the less will be the second component 

 (i.e., the inductance of the windings). It is, however, for 

 obvious practical reasons, chief amongst which is the import- 

 ance of having excellent insulation, not feasible to go very far 

 in the direction of intermixing the primary and secondary 

 windings. The inductance is greater the lower the magnetic 



FIG. 56. Diagram showing magnetic leakage in core-type transformer. 



reluctance of the path offered to the passage of magnetic flux 

 between the primary and secondary. This flux is termed the 

 leakage flux. To keep down the inductance it is important 

 that as much as possible of the magnetic flux shall be linked 

 both with the primary and secondary windings, i.e., it is 

 important that the magnetic flux shall be restricted to the 

 main magnetic circuit, so far as practicable. 



In Fig. 56 the coil marked P represents the primary and 

 the coil marked S represents the secondary. When the 

 secondary is delivering electricity to an external circuit, the 

 current in its windings flows in the opposite direction to that 

 of the current in the primary windings. Consequently if we 

 consider the conductors lying within the winding window, we 



