78 Scientific Proceedings, Royal Dublin Society. 



8 depends on the temperature T and pressure h of the atmosphere surrounding 

 the luie, and is given by 



9-96A 



^ ' 2T3~e' 



if 6 is expressed in degrees centigrade and h in inches of mercury. 



y is a factor depending on the roughness of surface of the conductor, and is 

 1 for pohshed round wires, 0'98 to 0'93 for roughened or weathered wires, 0'87 td 

 0'83 for seven-strand cable. 



a, b, f, I, V have the same significations as before. 



11. We can now set out in systematic form the scheme of calculation of a 

 single-phase or symmetrical three-phase line. 



We divide the scheme into five sections — (1) a statement of the data of the 

 problem, (2) the determination of the most economic section of conductor, (3) the 

 calculation of the line constants, (4) the calculation of the electrical quantities 

 required, and (5) the determination of the corona loss. 



(1) Data for one line. 



Frequency, / cycles per second. 



Voltage between wires at receiving end. 



Power delivered. 



Power factor of load, cos f. 



Effective average value of current C" delivered throughout the year. 



Length of line, I miles. 



Conductors spaced h inches mutually apart. 



Cost of conductor material, q pence per lb., and rate of interest and 



depreciation thereon, r per annum. 

 Value of power, s pence per unit. 

 Average atmospheric temperature, Q degrees centigrade, and pressure, h 



inches of mercury. 



(2) Determination of tlia most economical size of conductor. (See paragraph 8.) 



For copper, A' = -0043 C" J— sq. inches. 



For aluminium. A' = -010 C j± , i^.ehes. 



Choose the nearest standard size of conductor A sq. inches. 



« = /— inches for solid conductor. 



(3) Calcukction of line constants. 



V "0^3 V, -070 



^ - ~jf onins per niile for copper = — - ohms per mile for aluminium. 



Z = ( 8 + 74-1 X logjd — 1 X 10"* henrys per mile, 



a 



iT = 5 X 10 " mhos per mile. 



