Parallel operation of triple- and double-wound transformers with difference transformation ratios

Abstract

During the operation of electric-power systems, there is often a problem of splitting up the capacity of transformers installed on substations, which, as a rule, entails mounting two or more transformers in parallel instead of a single one, the total capacity of which is the same. In such replacement, there is a problem of uniform distribution of the load between transformers. When using transformers that have the same capacity and are structurally similar, uniformity of load distribution is reached achieved owing to symmetry of parallel circuits. However, if transformers with of different designs and various transformation ratios are connected, then uniformity of a capacity distribution between transformers is violated. With an increase in the total load current, in the case of double-wound transformer I and triple-wound transformer II connected in parallel, the secondary current of transformer I increases, as does its primary current, while the primary and secondary currents of transformer II decrease. In addition, the total current from the mains is less than the current of the primary winding of transformer I. With an increase in the loading current, the secondary current of transformer I increases and the secondary current of transformer II decreases. At the highest value of the secondary current of transformer II, the vector of primary current of this transformer advances the voltage vector by more than by 90°. In addition, the secondary winding of transformer II consumes active power from transformer I and returns it to its primary winding.