By the 1960s, the electric grids of developed countries had become very large, mature and highly interconnected, with thousands of 'central' generation power stations delivering power to major load centres via high capacity power lines which were then branched and divided to provide power to smaller industrial and domestic users over the entire supply area.
Do 1960-ih godina, električne mreže razvijenih zemalja su postale veoma velike, razvijene i imale su široku povezanost, a hiljade "centralnih" termoelektrana snabdevale su energijom glavne trafostanice putem dalekovoda velikih kapaciteta, koji su zatim razgranati i podeljeni kako bi obezbedili snagu manjim industrijskim i domaćim korisnicima u čitavoj oblasti snabdevanja.