Abstract :
This paper discusses secondary unit substations transformers (USTs) ranging from 300 kVA up through 2500 kVA with 34.5 kV maximum primary voltages and with secondary voltages 600 volts and below. The first part of this paper discusses USTs belonging to two general categories, liquid-type and dry-type (nonliquid type). Liquid types include a discussion of the presently available insulating fluids: mineral oil, high temperature hydrocarbon fluid, silicone fluids and the new vegetable based fluids. Dry types include a discussion of VPI polyester, VPE silicone, partial cast and full cast insulation systems. National Electric Code (NEC) 1999 requirements as they affect both liquid and dry type USTs for both outdoor and indoor locations are considered. The second part of the paper discusses the relative advantages of each UST within each category with respect to first cost, operating costs (losses), overload capability, fan cooling, space factor, environmental factors, sound levels and maintenance.
Keywords :
cooling; losses; maintenance engineering; organic insulating materials; polymers; power transformer insulation; silicone insulation; transformer oil; transformer substations; 300 to 2500 kVA; 34.5 kV; 600 V; National Electric Code 1999 requirements; VPE silicone; VPI polyester; dry-type transformers; environmental factors; fan cooling; first cost; full cast insulation systems; high temperature hydrocarbon fluid; indoor locations; insulating fluids; liquid-type transformers; losses; maintenance; mineral oil; operating costs; outdoor locations; overload capability; partial cast insulation systems; silicone fluids; sound levels; space factor; unit substation transformers selection; vegetable based fluids; Costs; Dielectric liquids; Hydrocarbons; Minerals; National electric code; Oil insulation; Petroleum; Substations; Temperature; Transformers;
