How transmission voltage is selected or optimized

Transmission voltage is stepped up from power plant in order to reduce the losses in transmission. But for every transmission line there is a particular fixed limit for voltage to be transmitted. Beyond this limit the rise in voltage will not result in any economical advantage. Cost analysis is required for finding the optimum voltage; this analysis includes calculating the cost of the conductors, cost of insulators, supports, transformers, switchgear, lightning arresters and cost of erection. All the total cost should be minimum for a particular voltage. 

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As the voltage increases the total capital cost first decreases and reaches a minimum point and then increases. So particular capital cost minimum point is the optimum value of the voltage for which power is to be transmitted. Along with capital cost, amount of power to be transmitted and distance for which power is to be transmitted is also considered.