Faoi ghnáththosca, déanann an ag obair system of electrical equipment, generally divided into continuous operation, short-term operation, continuous short-term operation system, The principle of luchtú ríomh is to replace the rated power of electrical equipment under different ag obair systems with the same long-term working system. The ríomh of distribution transformer load is a complicated process, therefore, it needs a lot of calculation and repeated verification by professional staff, in order to get the correct calculation results.