Pacific service magazine . Interior of Vaca-Dixon Substation. The machine in the foreground is the 40,000 kv-a synchronous condenser, the largest in the world. cent for interest and 4 per cent for depre-ciation, maintenance and operation,—a totalof 11 per cent. An annual load factor of at least 60 percent should be obtainable for a long trans-mission. 200 miles of 110 kv. twin line will cost$3,000,000 and can deliver 330,000, per year at 62^^ per cent loadfactor with an annual charge of $330,000or 1 mil per 200 miles of 220 kv. twin line will cost$6,000,000 and can deliver 1
Pacific service magazine . Interior of Vaca-Dixon Substation. The machine in the foreground is the 40,000 kv-a synchronous condenser, the largest in the world. cent for interest and 4 per cent for depre-ciation, maintenance and operation,—a totalof 11 per cent. An annual load factor of at least 60 percent should be obtainable for a long trans-mission. 200 miles of 110 kv. twin line will cost$3,000,000 and can deliver 330,000, per year at 62^^ per cent loadfactor with an annual charge of $330,000or 1 mil per 200 miles of 220 kv. twin line will cost$6,000,000 and can deliver 1,320,000, per year at 62^^ per cent loadfactor with an an-nual charge of$660,000 or y^ milper kilowatt costs of thenecessary receivingand regulating sub-stations will in-crease these costsconsiderably but inabout the sameproportion. Thesuperior economyof the highest prac-ticable voltage isapparent if largeamounts of powerare to be Claremont Substation, connecting the 110,000 volt transmission system withthe 11,000 volt distribution system at Oakland. Pacific Service Magazine 289 Having determined that 220 kv. is eco-nomically desirable let us review the prob-lems that must be —Insulation The first problem to consider is that ofline insulation. A 200 mile line will haveabout 1400 points of support with not iessthan 6 times as many complete insulators,probably 9,000 to 10,000 in all. Only afew switch and transformer bushings willbe required, hence their cost will not be amaterial factor even though their unit costis high. The only line insulators available todayfor the highest voltage lines are the sus-pension types composed of a number ofcomparatively small units flexibly coupledtogether and capable of resisting tensiononly. This type of insulator was intro-duced in 1907 and was first described be-fore the A. I. E. E. by E. M. Hewlett. The standard unit as now manufacturedhas a diameter of 10 inches, a
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